Updated on 2026/04/29

写真a

 
OKAMOTO AKIHIRO
 
Organization
Institute of Integrated Research Research Center for Autonomous Systems Materialogy Visiting Professor
Title
Visiting Professor
External link

Degree

  • 博士（工学） ( 東京大学大学院工学系研究科 )

Research Areas

  • Nanotechnology/Materials / Nanobioscience

Papers

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Books

  • Extracellular Electron Uptake Mechanisms in Sulfate-Reducing Bacteria

    岡本 章玄, Xiao Deng

    2020  （ ISBN:9789811547621 ）

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    Sulfate-reducing bacteria (SRB) are ubiquitous in anaerobic environments, particularly in marine sediments, and play crucial roles in the biogeochemical cycling of carbon, sulfur, and metals, the biosynthesis of minerals, and anaerobic metal corrosion. While SRB are generally considered to utilize diffusive organics and gases (e.g., hydrogen) as the electron donors, recent studies revealed that some SRB can use extracellular insoluble solids (e.g., electrodes and partner microbial cells in a consortium) as electron donors for energy acquisition. However, the mechanism had been ambiguous for a decade, due to the difficulty to distinguish electron uptake reaction and hydrogen evolution on the surface of solids. This chapter summarizes research backgrounds and electrochemical methods and shows example studies regarding the extracellular electron uptake mechanisms and thermodynamics in SRB. These aspects have critical implications in SRB physiology, biogeological and biophysical processes, and anaerobic iron corrosion.

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  • ELECTROCHEMICAL TECHNIQUES AND APPLICATION TO CHARACTERIZE SINGLE- AND MULTICELLULAR ELECTRIC MICROBIAL FUNCTIONS

    ムルガン ムラリダハラン, グイヨネ アレクシ, 齋藤 淳貴, ミラン ワヒード, 鄧 驍, 岡本 章玄

    2019 

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    ELECTROCHEMICAL TECHNIQUES AND APPLICATION TO CHARACTERIZE SINGLE- AND MULTI-CELLULAR ELECTRIC MICROBIAL FUNCTIONS

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  • Electrochemical Techniques and Applications to Characterize Single- and Multicellular Electric Microbial Functions

    齋藤 淳貴, ムルガン ムラリダハラン, 鄧 驍, グイヨネ アレクシ, ミラン ワヒード, 岡本 章玄

    2019  （ ISBN:9781119611103 ）

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    An introduction to the fundamental concepts and rules in bioelectrochemistry and explores latest advancements in the field

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MISC

  • Development of genetic and electrochemical diagnosis and inhibition technologies for invisible corrosion caused by microorganisms (Contract Research); FY2021 Nuclear Energy Science & Technology and Human Resource Development Project Reviewed

    2023.1

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    Language：Japanese   Publishing type：Internal/External technical report, pre-print, etc.  

    DOI： 10.11484/jaea-review-2022-045

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  • Pathogens electrogenicity as a tool for in-situ metabolic activity monitoring and drug assessment in biofilms

    Waheed Miran, Divya Naradasu, Akihiro Okamoto

    iScience   24 ( 2 )   2021.2

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    Language：English   Publishing type：Book review, literature introduction, etc.   Publisher：Elsevier Inc.  

    DOI： 10.1016/j.isci.2021.102068

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  • 電気細菌学者は電気羊の夢を見るか？

    岡本 章玄

    日本微生物生態学会誌   14 - 16   2020

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  • Extracellular electron transfer mechanism affected by bacteriophages infecting an iron-reducing bacterium, Shewanella oneidensis

    石原令梧, 岡本章玄, 岡部聡, 北島正章

    日本水環境学会年会講演集   54th   2020

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  • ブラック電気細菌はなぜ・どうやって電子を流すのか？電子移動を自在に操る鉄腐食細菌、病原細菌

    岡本 章玄

    Chemistry   66 - 67   2020

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  • ブラック電気細菌たちが来た

    岡本 章玄

    SEIBUTSU-KOGAKU KAISHI   549 - 549   2020

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  • 微生物燃料電池によるエネルギーと物質生産の同時実現へ向けて

    岡本 章玄

    月刊バイオインダストリー   ( 7 )   75 - 83   2018

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  • 金属腐食抑制への応用に向けた鉄還元細菌Shewanellaの溶菌性バクテリオファージの単離と特性解析

    石原令梧, 岡本章玄, 高木達馬, 岡部聡, 北島正章

    日本水環境学会年会講演集   52nd   2018

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Presentations

  • Kinetic Competition Between Extracellular Electron Transport and Upstream Reactions in Microbial Electrode Catalysis

    OKAMOTO, Akihiro, HASHIMOTO, Kazuhito, Saito Junki

    Pacific Rim meeting on electrochemical and solid-state science  2016.10 

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    Kinetic Competition Between Extracellular Electron Transport and Upstream Reactions in Microbial Electrode Catalysis

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  • Molecular Design for Catalysts of Microbial Extracellular Electron Transfer: Redox Active Molecules Bound with Outer-Membrane Cytochrome C in Shewanella Oneidensis MR-1

    OKAMOTO, Akihiro, Tokunou Yoshihide, HASHIMOTO, Kazuhito

    Pacific Rim meeting on electrochemical and solid-state science  2016.10 

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    Molecular Design for Catalysts of Microbial Extracellular Electron Transfer: Redox Active Molecules Bound with Outer-Membrane Cytochrome C in Shewanella Oneidensis MR-1

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  • Molecular mechanism of proton coupled electron transfer in outer-membrane flavocytochrome

    岡本 章玄, 徳納吉秀, 橋本 和仁

    第５４回日本生物物理学会年会  2016.11 

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  • Electric properties of Outer Membrane Flavocytochromes in Shewanella oneidensis MR-1

    OKAMOTO, Akihiro

    AP-ISMET 2016  2016.8 

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    Electric properties of Outer Membrane Flavocytochromes in Shewanella oneidensis MR-1

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  • Mirobial current produciton reflects kinetic competition between extracellular electron transport and upstream reaction

    Saito Junki, OKAMOTO, Akihiro

    AP-ISMET 2016  2016.8 

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    Mirobial current produciton reflects kinetic competition between extracellular electron transport and upstream reaction

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  • c-type cytochrome covered outer membrane and nanowires mediate extracellular electron uptake of sulfate reducing bacteria

    OKAMOTO, Akihiro, Deng Xiao

    AP-ISMET 2016  2016.8 

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    c-type cytochrome covered outer membrane and nanowires mediate extracellular electron uptake of sulfate reducing bacteria

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  • Electrochemical monitoring for extracellular electron transport kinetics

    OKAMOTO, Akihiro

    AP-ISMET 2016  2016.8 

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    Electrochemical monitoring for extracellular electron transport kinetics

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  • Characteristic of anaerobic respiration associated with extracellular electron transport

    岡本 章玄

    極限環境生物学会第17回シンポジウム  2016.11 

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  • Study of Intercellular electrochemical interaction by mappping technitue of gene expresion

    OKAMOTO, Akihiro

    「微生物叢と宿主の相互作用・共生の理解と、それに基づく疾患発症の  2016.12 

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    多様なヒト体内環境の微生物叢で個々の細菌がエネルギーを獲得する機構の理解は、その集団としての生態や細菌間相互作用を制御する上で極めて重要である。例えば、多種多様な細菌が不均一な環境で異なる表現型を有するバイオフィルム全体を特定の菌やタンパク質に着目した薬剤によって鎮静・除去することは難しいが、バイオフィルムの熱力学的なエコシステムを理解し、その根本を物理化学的に制御するようなアプローチは有効であると考えられる。近年、環境微生物学において「分子」を介さない「電子」による細胞間相互作用(Intercellular Electron Transport, IET)が嫌気エネルギー代謝において極めて重要な役割を果たしていることが明らかになってきている。[1]膜タンパクや導電性フィラメントなどの導電性のマトリックスを介して異種または同種の菌が細胞外へ電子を輸送し、集団内で電子エネルギーを分け合って共生する機構である。私たちは、独自の精密電気

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  • Extracellular Electron Transfer by an oral plaque pathogen: Streptococcus mutans UA159

    OKAMOTO, Akihiro

    日本化学会第97春季年会  2017.3 

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    We examined the EET capability of Streptococcus mutans UA159, by conducting whole-cell electrochemical measurements. S. mutans was added in a three-electrode system consisted of an indium tin-doped oxide (ITO) substrate as the working electrode at 37。�C containing 10mM glucose as sole electron donor.

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  • Dynamic structural change of outer-membrane cytochrome associated with extracellular electron transport

    岡本 章玄

    蛋白研セミナー『構造を基盤とする蛋白質科学における未解決問題』  2016.3 

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  • Exploration of novel enzyme driven by extracellular electron transport in Shewanella as a platform

    岡本 章玄

    「電気と微生物」小集会  2016.3 

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  • Extracellular Electron Uptake by Desulfovibrio ferrophilus Strain IS5 via Outer-Membrane C-Type Cytochrome

    OKAMOTO, Akihiro, Deng Xiao, HASHIMOTO, Kazuhito

    ASM meeting 2016  2016.6 

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    Microbially induced corrosion (MIC) under anaerobic conditions damages important energy infrastructure such as underground oil and gas pipelines, resulting in enormous economic losses that are estimated to be in the billions of dollars annually.1 Sulfate-reducing bacteria (SRB) commonly play a major role in promoting MIC in these environments; in particular, SRB are thought to not only produce corrosive H2S during dissimilatory sulfate reduction but also deplete molecular hydrogen formed on iron or FeS surfaces, thereby enhancing rates of anaerobic corrosion. However, the relatively slow kinetics of hydrogen evolution has raised questions regarding the role of hydrogen as a major electron carrier for MIC processes. Recently, using Fe(0) as a sole electron donor, Dinh et al. isolated severa

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  • Cariogenicity of Streptococcus mutans UA159 in dental cavity is promoted by biofilm acidification via extracellular electron transfer

    岡本 章玄, ディビア ナラダス

    第58回歯科基礎医学会学術大会  2016.8 

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  • Biofilm Acidification promoted via extracellular electron transfer by oral plaque mirobe Streptococcus mutans UA 159

    OKAMOTO, Akihiro, Divya Naradasu

    AP-ISMET 2016  2016.8 

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    Biofilm Acidification promoted via extracellular electron transfer by oral plaque mirobe Streptococcus mutans UA 159

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  • Proton transfer as a key for acceleration of the extracellular electron transfer by ound flavin with outer-membrane cytochrome c in Shewanella oneidensis MR-1

    OKAMOTO, Akihiro, Tokunou Yoshihide

    AP-ISMET 2016  2016.8 

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    Proton transfer as a key for acceleration of the extracellular electron transfer by ound flavin with outer-membrane cytochrome c in Shewanella oneidensis MR-1

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  • Membrane Cytochromes Enable Energy Acquisition in Energy- limited Environments

    OKAMOTO, Akihiro, Xiao, HASHIMOTO, Kazuhito

    環境微生物系学会合同大会2017  2017.8 

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    Membrane Cytochromes Enable Energy Acquisition in Energy- limited Environments

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  • Circular Dichroism Spectroscopy of Living Microbe Reveals Redox-Triggered Conformational Change of Heme Cofactors in Cytochromes

    岡本 章玄, 徳納吉秀, 橋本 和仁

    第55回日本生物物理学会年会  2017.9 

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  • NanoSIMS Analysis of Single Electrogenic Cell Reveals Feedback from Extracellular Electron Transport to Upstream Reactions

    岡本 章玄, 橋本 和仁

    第55回 日本生物物理学会年会  2017.9 

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  • Critical molecular structure in bound flavin cofactor to enhance hte rate of extracellular electron transport

    OKAMOTO, Akihiro, HASHIMOTO, Kazuhito

    International society for microbial electrochemistry and tech  2017.10 

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    Critical molecular structure in bound flavin cofactor to enhance hte rate of extracellular electron transport

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  • Microbial Electrocatalysts towards Environmental Technologies: Microbial Current Production Controlled by Coupled Proton Transfer

    岡本 章玄, 徳納吉秀, 橋本 和仁

    Interdisciplinary Symposium for Up-and-coming Material Scientist  2017.8 

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  • Ligation of riboflavin functionalizes outer-membrane cytochromes complex as biological diode in Geobacter sulfurreducens PCA

    OKAMOTO, Akihiro, Tokunou Yoshihide, HASHIMOTO, Kazuhito

    Extracellular Electron Transfer: Mechanisms and Opportunities  2017.8 

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    外膜シトクロムをダイオード化させるリボフラビン結合

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  • Multi-heme Cytochromes Found In Oxidized Sulfur Reducing Bacteria Mediate Direct Extracellular Electron Uptake

    OKAMOTO, Akihiro, Xiao, HASHIMOTO, Kazuhito

    Extracellular Electron Transfer: Mechanisms and Opportunities  2017.8 

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    Multi-heme Cytochromes Found In Oxidized Sulfur Reducing Bacteria Mediate Direct Extracellular Electron Uptake

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  • Ammonium Oxidation Coupled with Extracellular Electron Transport by Shewanella oneidensis MR-1

    岡本 章玄, 橋本 和仁

    環境微生物系学会合同大会2017  2017.8 

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  • Electron transport between microorganisms and electrodes kinetically controlled by coupled proton transport

    岡本 章玄

    Recent Progress on Interfacial Energy Conversion  2017.5 

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  • Proton transfer in outer-membrane flavocytochromes limit the rate of bacterial electron transport

    OKAMOTO, Akihiro, Tokunou Yoshihide, HASHIMOTO, Kazuhito

    2017 International Workshop on Electrified Interfaces for Energy  2017.5 

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    Proton transfer in outer-membrane flavocytochromes limit the rate of bacterial electron transport

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  • Proton Transfer in Outer-Membrane Flavocytochromes Coupled with Extracellular Electron Transport

    OKAMOTO, Akihiro, Tokunou Yoshihide, HASHIMOTO, Kazuhito

    24th International Symposium on Bioelectrochemistry and Bioenerg  2017.7 

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    外膜フラボシトクロム酵素を介したプロトン共役細胞外電子移動

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  • Outer Membrane Multi-heme Cytochromes Enable Extracellular Electron Uptake by Sulfate Reducing Bacteria

    OKAMOTO, Akihiro, Xiao, HASHIMOTO, Kazuhito

    International union of microbiological societies 2017  2017.7 

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    Outer Membrane Multi-heme Cytochromes Enable Extracellular Electron Uptake by Sulfate Reducing Bacteria

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  • In-situ electrochemical measurements for Intracellular enzymatic reactions

    岡本 章玄

    つくば医工フォーラム2017  2017.3 

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  • Extracellular Electron Transfer by oral plaque pathogen: A plausible cariogenesis mechanism

    OKAMOTO, Akihiro

    つくば医工フォーラム2017  2017.3 

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    Extracellular Electron Transfer by oral plaque pathogen: A plausible cariogenesis mechanism

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  • Direct Extracellular Electron Uptake by New Class of Outer Membrane c-type Cytochromes in Sulfur-Metabolizing Bacteria

    岡本 章玄

    日本化学会第97春季年会  2017.3 

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  • Ammonium oxidation with nitric oxide production by Shewanella oneidensis MR-1

    岡本 章玄

    日本化学会第97春季年会  2017.3 

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  • Ammonium Oxidation with Nitric Oxide Production by Shewanella oneidensis MR-1

    OKAMOTO, Akihiro, HASHIMOTO, Kazuhito

    IUMS2017  2017.7 

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    シワネラ菌による一酸化窒素生成を伴うアンモニア酸化反応

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  • MICROBIAL CATION AND ELECTRON OUTFLOW ACROSS THE OUTER MEMBRANE PROMOTES FERMENTATIVE ATP FORMATION

    岡本章玄, シャオ, 橋本和仁

    International union of microbiological societies 2017  2017.7 

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    MICROBIAL CATION AND ELECTRON OUTFLOW ACROSS THE OUTER MEMBRANE PROMOTES FERMENTATIVE ATP FORMATION

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  • MICROBIAL CATION AND ELECTRON OUTFLOW ACROSS THE OUTER MEMBRANE PROMOTES FERMENTATIVE ATP FORMATION

    OKAMOTO, Akihiro, Tokunou Yoshihide, HASHIMOTO, Kazuhito

    International union of microbiological societies 2017  2017.7 

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    MICROBIAL CATION AND ELECTRON OUTFLOW ACROSS THE OUTER MEMBRANE PROMOTES FERMENTATIVE ATP FORMATION

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  • Analysis on the single-cell metabolic pathway of dual isotope labeled bacteria with nanoscale secondary ion mass spectrometry

    岡本 章玄, 齋藤 淳貴

    日本微生物生態学会第 32 回沖縄大会  2018.7 

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    Single cell analyzing techniques are rapidly developing but have not widely succeeded in capturing metabolic pathway and activity of a single microbial cell at the same time due to the insufficient sensitivity. Here, we show that the assimilation ratio of carbon to nitrogen quantified by Nanoscale secondary ion mass spectrometry (NanoSIMS) reflects the metabolic pathway in individual cells of Shewanella oneidensis MR-1. After 24 hours of electrochemical incubation on the surface of electrode poised at +0.4 V vs standard hydrogen electrode in the presence of [1-13C]lactate as an electron donor and 15NH4+, the plot of 13C/Ctotal over 15N/Ntotal in individual cells gathered around a single linear line despite their variable metabolic rate. The slope of this linear line reflected the alteration of metabolic pathway induced by mutation and control of substrate concentration, suggesting that the ratio of assimilated 13C to 15N in single cells stands for their intracellular metabolic pathway. Thus, double isotope labeling of substrates for anabolic reaction allows the measurement of single cell metabolic pathway and activity at the same time.

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  • 微生物鉄腐食研究が与える異分野融合のチャンス

    岡本 章玄

    日本生物工学会2018年度大会  2018.9 

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  • Proton-Coupled Extracellular Electron Transport via Microbial Outer Membrane Flavocytochromes

    岡本 章玄

    2018 MRS Fall Meeging & Exhibit  2018.11 

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    Proton-Coupled Extracellular Electron Transport via Microbial Outer Membrane Flavocytochromes

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  • Low pH induced Extracellular Electron Transfer by an oral pathogen

    岡本 章玄, ナラダス ディビア

    Interdisciplinary Science & Technology for Safety and Quality of Life 9th Annual ISAJ Symposium  2018.12 

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    Maintaining the redox balance is a challenge for the microbes to sustain the fermentation, as primary fermenters in oral environment like S.mutans excretes acid end products or gases like H2, which creates highly reductive environment in oral biofilm and inhibit energy maximization and prohibits their redox balance. In environmental microbe, extracellular electron transport (EET) is used for NAD+ regeneration. However, such electron transport capability was not explored in oral pathogens. To study the potential involvement of EET in microbial fermentation in oral pathogens, we tested the EET capability in a well-studied fermentative oral pathogen Streptococcus mutans UA159 by in-vivo electrochemistry. S.mutans showed the EET capability. Our analysis revealed the electrogenic activity of S.mutans on electrode surface is coupled with glucose oxidation directly through a membrane bound redox enzymes. Microscopic observation heme stained S.mutans indicated that redox enzymes are highly expressed during the acid stress. Single cell activity by nanoSIMS revealed that EET has a role to activate the microbes that are less active in fermentation.

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  • 微生物鉄腐食研究が進める異分野融合の近況

    岡本 章玄

    微生物腐食分科会  2018.12 

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  • Long-range electron transfer in the conductive duel species aggregates of sulphate reducing bacteria and iron reducing bacteria

    岡本 章玄, ムルガン ムラリダハラン

    10th Asian Symposium on Microbial Ecology  2018.7 

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    We studied long range electron conduction in the duel species aggregates of the sulphate reducing bacteria (SRB), Desulfovibrio vulgaris and iron reducing bacteria (IRB), Shewanella oneidensis MR-1. These dissimilatory SRB found in sulphidic environments naturally accelerate precipitation of various phases of iron sulphides (FeSs) like pyrite, mackinawite, greigite and marcasite in their sediments. Metallic like conductivity of the tetragonal iron sulphides, mackinawite enables them to function as long-range electron conductors adjoining different redox environments. Recently it was reported that such metallic FeSs facilitate anaerobic bacterial respiration which are coupled with electron transport process to external solids, the so-called extracellular electron transport (EET). Current production from EET by the electrogenic IRB, S. oneidensis MR-1 was drastically increased by biomineralization of metallic mackinawite precipitates which performed as naturally occurring electrical wires. In the current work, the conductive nature of the coculture aggregates dominated by FeS precipitates was investigated by using interdigitated microelectrode arrays (IDAs) which were poised at +0.2 V Ag/AgCl reference electrode with lactate as the sole electron donor. Both SRB and IRB were found to be seen in the aggregates by fluorescent in-situ hybridization (FISH) analysis and the experimental data suggested the involvement of longrange electron transfer in the coculture aggregates in the presence of FeS precipitates. We will show the detailed electrochemical data from the biofilm on the IDAs, and discuss the conduction mechanism in the aggregates.

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  • Membrane Cytochromes Enable Energy Acquisition in Energy-limited Environments

    岡本章玄, 鄧 驍

    2018 JSME annual meeting & 10th ASME  2018.7 

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    Sulfate reducing bacteria (SRB) are ubiquitous in marine sediments, which are depleted in organics as energy source (B. B. Jorgensen et al. 2016). In such environments, H2 formed from water radiolysis, or water rock interactions has been considered as the main energy source, yet remained unclear to be sufficient to support the subsurface ecosystems or not. Recent findings showed several strains of sulfate reducing bacteria (SRB) can utilize solid-state electron donors, such as metallic iron or cathode, possibly via extracellular electron uptake (H. T. Dinh et al. 2004, X. Deng et al. 2015). Here, we examine the mechanism of SRB to respire with extracellular solids via direct electron uptake using Desulfovibrio ferrophilus IS5 as a model microbe. As outer membrane cytochromes (OMCs) are essential for iron-reducing bacteria to respire solids, we first sequenced the genome of IS5 to identify OMCs. As a result, we identified a gene cluster coding for OMCs. Further analysis of in vivo OMCs expression condition revealed that IS5 overexpressed twice more OMCs under lactate (soluble electron donor) limitation, which strongly suggest that IS5 can extract electrons from solids via OMCs. We will discuss about bioinformatical analysis in more detail and present microscopic images of cytochrome-stained

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  • Synergetic extracellular electron transfer from dual species in anaerobic conductive sediment

    岡本 章玄

    17th International Symposium on Microbial Ecology  2018.8 

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    Sediment microbial fuel cells (SMFCs) are currently being developed to provide persistent power for undersea devices over years. Previous studies suggested that the microbial communities change their environment in such a way that enhances electrical interaction among SMFCs. While microbial community structures have been well investigated in SMFCs, interspecies interactions have not been widely investigated under the influence of both anode and minerals in the sediment. Here, we study dual species biofilm of iron-reducing (IRB) and sulfate-reducing bacteria (SRB), which often dominate the microbial community in the anode side of SMFCs. We performed electrochemical inoculation using the genus Shewanella and Desulfovibrio in the presence of lactate as a sole electron donor in our batch electrochemical system constructed with Indium tin-doped oxide (ITO). Inoculation of the two strains on electrode surface in anodic chamber at +0.4 V vs SHE caused more-than 50 times higher current production compared with single culture of either IRB or SRB, associated with the biosynthesis of black iron sulfide (FeS) precipitation. Fluorescence in-situ hybridization and X-ray Photoelectron Spectroscopy revealed the formation of IRB and SRB aggregation on the surface of electrode with the formation of highly conductive FeS phases. Because IRB and SRB supposedly compete each other for acquiring electron donor agents in natural environments, these data suggest that the presence of biosynthesized FeS may alter the interspecies interaction between IRB and SRB for synergetic current production. We will discuss the mechanism of synergetic current production by analyzing the single cell activity of SRB and IRB.

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  • Simultaneous analysis of single-cell metabolic pathways and bacterial activity with nanoscale secondary ion mass spectrometry (NanoSIMS)

    岡本 章玄, 齋藤 淳貴

    17th International Symposium on Microbial Ecology  2018.8 

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    Single cell analyzing techniques are rapidly developing but have not widely succeeded in capturing metabolic pathway and activity of a single microbial cell at the same time due to the insufficient sensitivity. Nanoscale secondary ion mass spectrometry (NanoSIMS) has quite high sensitivity among the single cell analytical methods and has already been applied to analyze the metabolic activity of the cells. Here, we show that the fixation ratio of carbon to nitrogen quantified by NanoSIMS reflects the metabolic pathway in individual cells of Shewanella oneidensis MR-1. After 24 hours of electrochemical incubation on the surface of electrode poised at +0.4 V vs standard hydrogen electrode in the presence of 13C-lactate as an electron donor and 15N-NH4+, the plot of 13C/Ctotal and 15N/Ntotal for individual cells of MR-1 gathered around a single linear line despite their variable metabolic rate. This ratio reflected the alteration of metabolic pathway, which was induced via mutation and control of substrate concentration, suggesting double isotope labeling of substrates allows the measurement of single cell metabolic pathway and activity at the same time.

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  • 発電する細菌のサイエンスとその利用の新展開

    岡本 章玄

    愛媛県バイオマス利活用促進連絡協議会  2019.2 

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  • Electrochemical ammonium oxidation with an electroactive microbe

    岡本 章玄, 齋藤 淳貴

    MANA International Symposium 2018  2018.3 

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    Microbial Fuel Cell (MFC) is a technology for removing organic matters in wastewater while producing electricity. However, because extracellular electron transport (EET)-capable bacteria do not have known enzymes to catalyze NH4+ oxidation, MFC capable of NH4+ treatment has not been realized. Here, we examined the potential of NH4+ oxidation by metal-reducing bacteria Shewanella oneidensis MR-1 capable of EET. Upon the addition of MR-1 to anaerobic three electrode system poised at +0.4 V (vs. SHE), the presence of NH4+ as a sole electron donor caused current increase and NH4+ concentration decrease, which were associated with the production of nitric oxide (NO) confirmed by isotopic analysis and NO-specific fluorescent imaging. Also, the anabolic reaction coupled to NH4+-oxidizing current production was observed by secondary ion mass spectroscopy with nano-scale spatial resolution. Given known gene for NH4+ oxidation is not possessed by MR-1, our data strongly suggest that unknown genes for NH4+ oxidation exist in the genome of MR-1, implying the possibility of MFC for treating NH4+.

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  • Acid stress induced Extracellular Electron Transfer by an oral pathogen Streptococcus Mutans UA159

    岡本 章玄, ナラダス ディビア

    MANA International Symposium 2018  2018.3 

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    Streptococcus mutans, the major causative agent of human dental caries, lives almost exclusively as tenacious biofilms on the tooth surface and survive in various kinds of environmental stresses like nutrient availability, pH, temperature, oxygen tension, saliva, and shearing force. Primary fermenters in oral environment like S.mutans excretes acid end products or gases like H2 which creates a redox environment with in oral community and inhibit energy maximization. Hence, long-range electron transport would be highly energy conservative for the microbes in order to maintain the redox balance. Extracellular electron transport (EET) capability was not explored in oral pathogens. In our study, we tested the EET capability in a fermentative oral pathogen S.mutans by in-vivo electrochemistry for the first time. S.mutans showed the EET capability on electrode surface and such EET capability is induced upon acid-stress exposure during preculture and is insignificant in no pH-stress cells. Our analysis revealed the electrogenic activity of S.mutans on electrode surface is coupled with glucose oxidation directly through a membrane bound redox enzymes.

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  • Conformational change of multi-heme electron conduit in cytochromes c in whole-cell

    岡本 章玄, 徳納 吉秀

    JSPS 10th HOPE meeting  2018.3 

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    Some microbes have an ability to transport electrons to solid substrate or electrode located extracellularly, termed as extracellular electron transport (EET). To accomplish the EET process, they rationally arrange multi-hemes in c-type cytochromes at bacterial outer-membrane (OM c-Cyts) as biological electron conduit. Therefore, molecular-level mechanisms managing the efficient long-range electron transport in the multi-heme conduit have been investigated based on the crystal structure of OM c-Cyts in Shewanella oneidensis MR-1 (e.g. MtrC protein). However, recent whole-cell electrochemical analyses have revealed that MtrC in whole-cell has distinct property from purified MtrC or crystal structure, e.g. its kinetics of electron transport, suggesting that MtrC changes its structure specifically in whole-cell. In this study, we report that circular dichroism (CD) spectrum in Soret band of whole Shewanella cells reflects the conformation and interaction of multi-hemes in native MtrC. Comparison of the CD spectra of Shewanella and purified MtrC suggested that some of hemes in reduced MtrC change the orientation specifically in whole-cell, which may strikingly impact on the EET kinetics of living Shewanella. In the poster, we will discuss about the detailed heme arrangement in native MtrC and its link with the EET kinetics in Shewanella based on magnetic CD spectroscopy, pH titration, and molecular-level simulation using TD-DFT

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  • Molecular design of electrocatalysts towards enhancement of interfacial electron transport between microorganism and electrode

    橋本 和仁, 徳納 吉秀, 岡本 章玄

    日本化学会第98回春季年会  2018.3 

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    An iron-reducing bacterium, Shewanella oneidensis MR-1, has an ability to transport respiratory electrons generated from cell inside to extracellular

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  • Whole-cell Circular Dichroism Spectroscopy Reveals Inter-Heme Interactions in Cell Surface Cytochrome c

    TOKUNOU, Yoshihide, OKAMOTO, Akihiro, HASHIMOTO, Kazuhito

    IGER International Symposium on Cell Surface Structures 2017  2017.11 

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    Whole-cell Circular Dichroism Spectroscopy Reveals Inter-Heme Interactions in Cell Surface Cytochrome c

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  • How do small molecules govern the rate of microbial electrogenic respiration?

    OKAMOTO, Akihiro

    IGER International Symposium on Cell Surface 2017  2017.11 

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    Insights into the rate enhancement of extracellular electron transport in iron-reducing bacteria, by quinone and flavin analogues

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  • Currents in human mouth: Oral pathogen Capnocytophaga ochracea proceeds extracellular electron transportation

    岡本 章玄, Shu ZHANG

    MANA International Symposium 2018  2018.3 

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    Extracellular electron transportation (EET) has been discovered to elucidate the microbial energy production mechanisms in the natural environment, and reveals the group of microbe powered by EET. For example, Geobacter and Shewanella rely on the EET process for anaerobic respiration to support growth in the mineral forming environments . Human body is also an important “environment” for microbial colonization. However, the role of EET in human microbiome scarcely investigated, while activity of human microbiome critically influences the host’s health. Thus, our study investigates microbial metabolism under EET condition using a well-known subgingival oral pathogen, Capnocytophaga ochracea, which mainly harvest energy by fermentation. To study their EET capability, we established a three-electrode electrochemical reactor with an indium tin-doped oxide (ITO) electrode as a working electrode and a sole electron acceptor, and monitor the electron transport from bacteria as current production at +0.2 V vs Ag/AgCl KCl sat.. Within 24-hour’s incubation amended with 10 mM glucose, approximately 150 nA was detected, indicating the occurrence of EET with C. ochracea attached on the ITO electrode. The increase of cell density, the absence of oxygen and nutrient supply were found to enhance the current generation, suggesting the microbial metabolism was the source of current generation. Moreover, the existence of EET pathway of redox-active membrane enzymes in C. ochracea was visualized by TEM. In the poster presentation, we will discuss about the dataset of nanoscale secondary ion mass spectrometry (NanoSIMS) to quantitatively analyze the anabolic activity of 13C-labeled glucose at the single cell level. Our results are the first attempt to reveal the EET capability of oral pathogens in human microbiome. The divergent metabolic features and microbial lifestyle discovered in this study would be a tremendous expansion in human microbiome research and provide practical references of disease treatment in medical field.

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  • Whole-cell Circular Dichroism Spectroscopy Reveals Redox-Triggered Conformational Change of Multi-Hemes Conduit in Cytochromes c

    岡本 章玄, 徳納 吉秀

    MANA International Symposium 2018 Towards Perceptive Nanomaterials, Devices and Systems  2018.3 

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    C-type cytochromes located at bacterial outer-membrane (OM c-Cyts) designs multi-hemes acting as nanoelectronic conduits for linking the respiratory chain of bacteria to external solid substrates. Towards development of practical bioelectronics applications, the multi-heme alignment and interactions realizing the highly efficient extracellular electron transport (EET) process has been extensively studied, based on the crystal structure of OM c-Cyts in Shewanella oneidensis MR-1 e.g. MtrC protein. However, our whole-cell electrochemical analyses have revealed that MtrC in whole-cell has distinct property from crystal structure, e.g. its kinetics of electron transport, suggesting that MtrC changes its structure specifically in whole-cell. In this study, we report that circular dichroism (CD) spectrum around Soret band of whole Shewanella cells reflects the conformation and interaction of multi-heme in native MtrC. Comparison of the CD spectra of Shewanella and purified MtrC suggested that some of hemes in reduced MtrC change the orientation specifically in whole-cell, which may strikingly impact on the EET kinetics of living Shewanella. In oxidized state, the Soret CD signal of MtrC in whole-cell showed almost identical intensity with purified MtrC, indicating that the native MtrC arranges hemes with almost identical conformation with purified MtrC in oxidized state. On the other hand, once the native MtrC was reduced, the Soret CD intensity was weakened about 50 % with suppression of characteristic splitting signals observed in the purified MtrC. These differences in CD spectrum of reduced MtrC strongly suggest that the inter-hemes interaction in MtrC specifically changes in whole-cell. In the poster, we will discuss about the detailed heme alignment in the native MtrC and its link with the EET kinetics in Shewanella based on the data of magnetic CD spectroscopy, pH titration, and molecular-level simulation using TD-DFT.

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  • Perspective for fundamentals and applications in Microbially-induced Corrosion

    岡本 章玄

    Biocorrosion – any progress in reality? A Conceptual Workshop  2018.7 

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    Importance of metabolic pathway in addition to metabolic activity and community structure (16s rRNA analysis) Missing key player? How does bacteriophage influence ecology in corrosive biofilm? Biological impact of FeS nanoparticle

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  • Extracellular electron transport(EET) Recovers Fermentation suppressed by Highly Reductive Potential in Streptococcus mutans

    岡本 章玄, ナラダス ディビア

    32nd ANNUAL MEETING of JAPANESE SOCIETY for MICROBIAL ECOLOGY & 10th ASIAN SYMPOSIUM on MICROBIAL ECOLOGY(ASME)  2018.7 

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    The redox balance is a challenge for the microbes to sustain the fermentation, as primary fermenters in oral environment like S.mutans excretes acid end products or gases like H2, which creates highly reductive environment in oral biofilm and inhibit energy maximization and prohibits them to maintain the redox balance. In environmental microbe, extracellular electron transport (EET) is used for NAD+ regeneration, in which microbes transfer their metabolically generated electrons to outside of cell to an external electron acceptor. However, such electron transport capability was not explored in oral pathogens. To study the potential involvement of EET in microbial fermentation in oral pathogens, we tested the EET capability in a well-studied fermentative oral pathogen Streptococcus mutans UA159 by in-vivo electrochemistry. S.mutans showed the EET capability to an ITO electrode surface coupled with glucose oxidation leading to efficient lactate production. In contrast, open circuit condition caused 80% less lactate production than EET condition, and the ethanol production significantly increased.

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  • Circular Dichroism spectroscopy for Engineered E.coli surface cytochrome detection

    岡本 章玄, ロン シズ

    ISMET7 International Society for Microbial Electrochemistry and Technology Global Conference  2019.10 

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    Introducing the extracellular electron transfer (EET) pathway of Shewanella into Escherichia coli is conducive to controlling the processes of bioelectrochemical remediation, bioelectrosynthesis and other applications. Previous studies showed that upregulation of outer-membrane c-type cytochromes (OM c-Cyts) proteins by Isopropyl β-D-Thiogalactoside (IPTG) little increased the electron transfer rate. One of potential explanations is discorder of heme alignment in synthesized OM c-Cyts proteins in engineered Escherichia coli, non-native host. To prove this hypothesis, however, new methodologies to monitor the inter-heme interaction in OM c-Cyts in vivo are required. Here, we used circular dichroism (CD) spectroscopy to analyze heme alignment in the specific protein in OM c-Cyts, MtrC, in engineered E. coli with cymAMtrCAB. Because the concentration of MtrC in 10 times lower than S. oneidensis MR-1, the CD signal in Sort absorption band was scarcely detected. We therefore used the integrating sphere to enhance the signal by applying high cell density solution. As we expected, signal intensity increased, and peak shift in CD signal was confirmed upon the addition of electron donor, lactate, associated with the shift of absorption peak from 410 nm to 420 nm. We also confirmed a clear linear relationship between the CD signal peak intensity and the amount of MtrC quantified by electrophoresis. We will discuss the data of electrochemical characterization and temperature control to compare the electron conduction property of MtrC in engineered E. coli with native S. oneidensis MR-1.

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  • Low Extracellular Electron Transport Facilitate Fermentative Metabolism in oral Pathogen: Possibility of Electrical Symbiosis in Oral plaque

    岡本 章玄, ナラダス ディビア

    ISMET7 International Society for Microbial Electrochemistry and Technology Global Conference  2019.10 

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    The Human oral environment contains highly diverse microbial lifestyles and exclusively lives as biofilm communities1, where exists an oxygen gradient. The export of excess electrons would be beneficial in oral biofilm physiology as redox homeostasis is a major crisis for fermentative microbes in case of biofilm-associated diseases2-4. Here we show that the export of excess reductants to the cell exterior via extracellular electron transport (EET)5 is critical for the maintenance of redox balance in an oral pathogen S. mutans. Whole-cell electrochemistry, metabolite analysis coupled with nanoSIMS have revealed that, although the coulombic efficiency of EET was less than 0.1%, EET shifted the fermentation pathway from ethanol to lactate with enhanced anabolic activity. Use of redox balance repressor rex gene mutant showed that Rex mediated the redox balance with electron export having high sensitivity to NAD+. Since a little electron transport has shown a significant impact, Rex-EET coupling may be important for redox balance in the polymicrobial biofilms. Such rex having EET microbes6 showed higher identity with that of S. mutans compared to non-EET microbes. We will discuss the EET capability and surface redox enzymes’ redox potentials of other predominant oral pathogens, which showed redox energy gradients in alliance with the microbial arrangement of oral plaque7 implying the possibility of interspecies electron export in oral biofilm. Electron transport with redox gradient from anaerobic bottom to the aerobic surface would enable the utilization of the oxygen as a terminal electron acceptor and maintain the redox balance in polymicrobial biofilm.

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  • Ubiquitous Transmembrane Electric Conduit in Microbial World

    岡本 章玄

    MANA- i-MATE Joint Symposium  2019.11 

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    Outer membrane c-type cytochrome (OM c-Cyt) complexes with twenty heme centers function in unison as a biological “electron conduit” to transport electrons 20 nm or more to the cell exterior in several genera of iron-reducing or -oxidizing bacteria (Fig. 1). These bacteria couple metabolic reactions and direct electron transport with extracellular solids by OM c-Cyts. Recently, new transmembrane proteins were identified in marine sulfate-reducing bacteria Desulfovibrio ferrophilus IS5 [1] and food-borne pathogen Listeria monocytogenes [2]. Therefore, the kinetics of this microbial electron transport, referred as extracellular electron transport (EET), has implications for bioenergy or biochemical production [3], iron corrosion [1], and human health [2, 4]. To these ends, we study electron transport mechanisms through the transmembrane biological electric conduit by pioneering whole-cell physico-chemical methodology combined with molecular-biological approaches [5]. We will discuss about the kinetics of proton transport associated with EET via an OM c-Cyt complex by solvent kinetic isotope effect, direct observation of unique heme alignment in an intact cell, and potential diversity and distribution of EET-capable bacteria in nature.

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  • 電気細菌による嫌気鉄腐食反応機構と応用へ向けた課題

    岡本 章玄

    NIMSインフラ構造材料パートナーシップ 2020年度第1回研究会  2020.8 

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  • Open up extracellular nanoparticles! -Their diversity and biodynamics-

    岡本 章玄

    第58回 日本生物物理学会年会  2020.9 

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  • Interplay of low electron export and redox-repressor rex in modulation of pathogen’s metabolism – a new form for antibiotic assessment

    岡本 章玄, ナラダス ディビア

    1st virutual meeting ISMET 2020  2020.10 

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    ”Interplay of low electron export and redox-repressor rex in modulation of pathogen’s metabolism – a new form for antibiotic assessment”

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  • Effects of electric current on deep-sea hydrothermal vent Epsilonproteobacteria.

    岡本 章玄, 武藤 久

    マクロ生物学百花繚乱  2019.11 

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    深海底熱水活動域では、海底から噴出する熱水に含まれる還元的無機化合物が、現場に見られる生態系にとってほぼ唯一のエネルギー源であると考えられてきた。だが近年、深海底熱水活動域では、還元的な熱水と酸化的な海水が導電性の硫化鉱物を介して接することで電流が生成していることが明らかとなった。既知の鉄酸化細菌のなかには電気エネルギーを利用し、二酸化炭素から有機物を合成する能力を持つものが知られている。これらのことから、深海底熱水活動域において、電気をエネルギー源とする（微）生物活動（特に一次生産）の可能性が指摘・検証されるようになってきた。例えば、深海底熱水活動域に由来するチムニーサンプルを電気培養し、Shewanella属細菌や、Thermococcales目およびArchaeoglobales目アーキアのような従属栄養細菌が集積培養されるなど、熱水活動域に見られる微生物群集の電流に対する反応が報告されている。しかしながらこれまでの研究において、世界各地の深海底熱水活動域に優占して検出される絶対化学合成独立栄養微生物＝イプシロンプロテオバクテリアに及ぼす電流の影響を解析した例はなかった。そこで本研究では、過去の研究において深海底熱水活動域から得たイプシロンプロテオバクテリア分離株の電気化学的特性、特に電気エネルギーがその増殖に及ぼす影響を検証することを目的とした。 深海底熱水活動域に優占するイプシロンプロテオバクテリアの代表的な分離株について、はじめにdiaminobenzadine (DAB)染色に供し超薄切片を作成したところ、いずれも細胞外膜が強く染色され、電気エネルギーの利用に必要な膜表面の電子伝達酵素の存在が示唆された。次に、当該分離株の細胞外電子受容能（=電気利用能力）の検証のため、熱水活動域で確認された電気化学的条件下での電気培養を実施し、電流値の変化を記録しながら細胞数増殖、培養可能細胞数の変動、チオ硫酸イオン・硝酸イオン量の変動を調べた。対象とした中等度好熱細菌株では、増殖可能温度範囲内の40℃および範囲外の10℃で細胞外からの電子取り込みを示唆する電流値の変化が確認されたが、細胞数および培養可能細胞数は減少し、チオ硫酸イオンおよび最終電子受容体として添加した硝酸イオンは測定誤差が大きく明らかな消費が確認できなかった。細胞外電子受容能をもつ海洋性硫酸還元菌では、電気を利用するにもかかわらず細胞増殖が起きない例が知られており、今回対象にした分離株でみられた、電子取り込みを示唆する電流値の変化をするが細胞増殖は確認できなかったことと一致する。

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  • FeGenie: a bioinformatics tool and database to identify microbial iron-related genes and gene operons in genomes and metagenome assemblies

    Nancy Merino, 岡本 章玄

    The Gordon Research Seminar on Merging and Emerging Disciplines in Geobiology  2020.1 

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    Although iron is an abundant metal within the Earth’s crust, most natural ecosystems are iron limited due to the spontaneous oxidation of ferrous iron to insoluble ferric (oxy)hydroxides. Most living organisms require iron, forcing microorganisms to evolve mechanisms for dealing with iron limitation. Indeed, microorganisms possess a wide range of enzymes responsible for iron scavenging, transport, and storage. In some environments, where iron concentrations are not limiting, some microorganisms are capable of using iron as an electron donor or acceptor, with both groups deriving energy from their respective iron redox activities. Over the past few decades, more than 200 genes involved in iron cycling pathways have been identified. Many of these genes share apparent sequence homologies with ones that seemingly have no iron-related functions but are part of operons known to be involved in iron cycling (e.g., siderophore synthesis genes). There are also a few genes known to be involved in iron redox, but these genes are typically not annotated as such in routine annotation tools (e.g., InterProScan and Prokka). To address the present ambiguities with respect to iron-related pathways and to aid in the identification of iron-related genes and operons, we present a manually-curated database, broken down into 10 categories: iron transport, heme transport and degradation, siderophore synthesis and transport, iron gene regulation, iron redox, iron storage, and magnetosome formation. We then developed a bioinformatics tool, FeGenie, which takes (meta)genome assemblies as input for the identification of known iron-related pathways.

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  • Genomic Characterization of an Uncultivated Actinobacterial Acetogen from a Serpentine-Hosted Environment, Hakuba Happo Hot Springs

    Nancy Merino, 岡本 章玄

    The Gordon Research Seminar on Geobiology  2020.1 

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    Although iron is an abundant metal within the Earth’s crust, most natural ecosystems are iron limited due to the spontaneous oxidation of ferrous iron to insoluble ferric (oxy)hydroxides. Most living organisms require iron, forcing microorganisms to evolve mechanisms for dealing with iron limitation. Indeed, microorganisms possess a wide range of enzymes responsible for iron scavenging, transport, and storage. In some environments, where iron concentrations are not limiting, some microorganisms are capable of using iron as an electron donor or acceptor, with both groups deriving energy from their respective iron redox activities. Over the past few decades, more than 200 genes involved in iron cycling pathways have been identified. Many of these genes share apparent sequence homologies with ones that seemingly have no iron-related functions but are part of operons known to be involved in iron cycling (e.g., siderophore synthesis genes). There are also a few genes known to be involved in iron redox, but these genes are typically not annotated as such in routine annotation tools (e.g., InterProScan and Prokka). To address the present ambiguities with respect to iron-related pathways and to aid in the identification of iron-related genes and operons, we present a manually-curated database, broken down into 10 categories: iron transport, heme transport and degradation, siderophore synthesis and transport, iron gene regulation, iron redox, iron storage, and magnetosome formation. We then developed a bioinformatics tool, FeGenie, which takes (meta)genome assemblies as input for the identification of known iron-related pathways.

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  • Electrochemical catalytic function of membrane vesicle from bacteria

    岡本 章玄

    第93回日本細菌学会総会  2020.2 

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  • Transmembrane Electric Wire Synthesized in Living Bacteria

    岡本 章玄

    MANA International Symposium  2019.3 

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    Transmembrane multi-heme c-type cytochrome (OM c-Cyt) complexes function in unison as a biological “electron conduit” to make long-distance electron transport (20 nm or more) across the outer membrane to the cell exterior in several genera of iron-reducing or -oxidizing bacteria (Fig. 1). The ability of the multi-heme alignment and interaction to promote highly efficient long-range electron transport under non-equilibrium conditions has attracted biophysicists and biochemists for nanoscale electronic applications. Also, the kinetics of this microbial electron transport, referred as extracellular electron transport (EET), has significant implications for controlling the rate of microbial reactions during bioenergy or biochemical production, iron corrosion, and natural mineral cycling. To these ends, we study electron transport mechanisms through the transmembrane biological electric conduit by pioneering whole-cell physico-chemical methodology combined with molecular-biological approaches. In the presentation, we will discuss about the role of proton transport associated with EET,1 flexible heme alignment in OM c-Cyts,2 and our recent discovery of novel clade of OM c-Cyts from iron-corrosion bacteira.3

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  • FeGenie: a bioinformatics tool and database to identify microbial iron-related genes and gene operons in genomes and metagenome assemblies

    Nancy Merino, 岡本 章玄

    2019 NeLLi – Symposium on New Lineages of Life  2019.4 

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    Although iron is an abundant metal within the Earth’s crust, most natural ecosystems are iron limited due to the spontaneous oxidation of ferrous iron to insoluble ferric (oxy)hydroxides. Most living organisms require iron, forcing microorganisms to evolve mechanisms for dealing with iron limitation. Indeed, microorganisms possess a wide range of enzymes responsible for iron scavenging, transport, and storage. In some environments, where iron concentrations are not limiting, some microorganisms are capable of using iron as an electron donor or acceptor, with both groups deriving energy from their respective iron redox activities. Over the past few decades, more than 200 genes involved in iron cycling pathways have been identified. Many of these genes share apparent sequence homologies with ones that seemingly have no iron-related functions but are part of operons known to be involved in iron cycling (e.g., siderophore synthesis genes). There are also a few genes known to be involved in iron redox, but these genes are typically not annotated as such in routine annotation tools (e.g., InterProScan and Prokka). To address the present ambiguities with respect to iron-related pathways and to aid in the identification of iron-related genes and operons, we present a manually-curated database, broken down into 10 categories: iron transport, heme transport and degradation, siderophore synthesis and transport, iron gene regulation, iron redox, iron storage, and magnetosome formation. We then developed a bioinformatics tool, FeGenie, which takes (meta)genome assemblies as input for the identification of known iron-related pathways.

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  • 口腔内細菌叢における細胞外電子移動に関する研究

    岡本 章玄

    第92回日本生化学会大会  2019.9 

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  • Extracellular electron transport mechanism for microbial electrode catalysis

    岡本 章玄

    The 8th Asian Conference on Colloid & Interface Science  2019.9 

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    Outer membrane c-type cytochrome (OM c-Cyt) complexes with twenty heme centers function in unison as a biological “electron conduit” to transport electrons 20 nm or more to the cell exterior in several genera of iron-reducing or -oxidizing bacteria (Fig. 1). The kinetics of this microbial electron transport, referred as extracellular electron transport (EET), has implications for controlling the rate of microbial reactions during bioenergy or biochemical production [1], iron corrosion [2], and natural mineral cycling. To these ends, we study electron transport mechanisms through the transmembrane biological electric conduit by pioneering whole-cell physico-chemical methodology combined with molecular-biological approaches [3]. We will discuss about the kinetics of proton transport associated with EET via an OM c-Cyt complex by solvent kinetic isotope effect, direct observation of unique heme alignment in an intact cell, and potential diversity and distribution of EET-capable bacteria in nature.

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  • Synergetic current generation across conductive bacterial networks in biomineralized coculture

    岡本 章玄, ムルガン ムラリダハラン

    ISMET7 International Society for Microbial Electrochemistry and Technology Global Conference  2019.10 

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    Language：English   Presentation type：Oral presentation (general)  

    edimental Microbial Fuel Cells (SMFCs), an alternative renewable source, is getting importance because of low-maintenance and cost effectiveness. Proper knowledge on electricity generation mechanism in SMFCs is crucial to enhance their overall performances. At the anode of SMFCs, the iron reducing bacteria (IRB) conduct excellent extracellular electron transport (EET) in sediment containing dissimilatory sulphate reducing bacteria (SRB). While IRB and SRB may compete for limited energy sources, SRBs biomineralize tetragonal forms of iron monosulphides with metallic like conductivity, which improves electricity generation in SRB and IRB by functioning as electron conductors adjoining various redox environments. However, the interactions among SRB, IRB and FeS nanoclusters has not been investigated. In this work, we elucidated the impact of biomineralized FeS on the overall anodic current generation in the SRB and IRB cocultures. We performed electrochemical measurements to study the current generation with Desulfovibrio vulgaris (SRB) and S. oneidensis MR-1 (IRB) in a three-electrode electrochemical reactor with indium tin-doped oxide coated glass as working electrode poised at 200 mV vs Ag/AgCl KCl sat. Our observation showed that the biomineralization of FeS nanoclusters promoted synergetic enhancement of current generation. Electrochemical gating assays with the interdigitated array (IDA) electrodes showed long-range electron conduction in the bacterial-FeS bioagglomerates formed on the anode surface. We observed a conductive coculture bacterial network only in the presence of FeS bioagglomerates. We would discuss the localization of each bacteria in the 100 µm thick biofilm, and the potential synergetic mechanisms of SRB and IRB for anodic current generation enhancement.

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  • Extracellular Electron Transport by Human Gut Bacteria: Electrochemical Techniques for Isolation and Characterization

    岡本 章玄, ミラン ワヒード

    ISMET7 International Society for Microbial Electrochemistry and Technology Global Conference  2019.10 

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    Extracellular electron transfer (EET) is a ubiquitous strategy for microbial anaerobic respiration, and is mainly responsible for global biogeochemical cycling of metals. The mechanisms of outward EET are well understood for two model systems, Shewanella and Geobacter, both of which employ multiheme cytochromes to provide an electron pathway to the cell exterior in anoxic natural environments. However, as for the human microbiome which significantly impacts our health, the role and importance of EET has not been widely investigated. In this study, we enriched and isolated the EET-capable bacteria from human gut microbes using an electrochemical enrichment method and characterized the metabolism that couples with EET (Fig. 1). Upon the use of energy-rich or minimum media (with acetate or lactate) for electrochemical enrichment with the human gut sample at an electrode potential of +0.4 V vs SHE, both culture conditions showed significant current production. However, EET-capable pure strains were enriched specifically with minimum media, and subsequent incubation using a 𝛿-MnO2-agar plate with lactate or acetate led to the isolation of two EET-capable microbial strains, Gut-S1 and Gut-S2, having 99% of 16S rRNA gene sequence identity with Enterococcus avium (E. avium) and Klebsiella pneumoniae (K. pneumoniae), respectively. While the enrichment involved anaerobic respiration with acetate and lactate, further electrochemistry with E. avium and K. pneumoniae revealed that the glucose fermentation was also coupled with EET. These results indicate that EET couples not only with anaerobic respiration as found in environmental bacteria, but also with fermentation in the human gut.

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  • 発電細菌・固体界面における膜タンパクを介した電子とイオン移動研究の最前線

    岡本 章玄

    第15回固体イオニクスセミナー  2019.9 

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  • In-Situ Biosynthetically Produced Iron Sulfide Nanocluster by Sulfate reducing bacteria Enhanced Anodic Current Generation in Microbial Fuel Cells

    ムルガン ムラリダハラン, ミラン ワヒード, 岡本 章玄, 増田 卓也, Dae Sung Lee

    5th International Water Industry Conference 2019  2019.9 

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    A microbial fuel cell (MFC) is a device that converts chemical energy to electrical energy with the aid of microorganisms. In MFCs, current generation by sulfate reducing bacteria (SRB) is known to produce by the anodic oxidation of sulfide which is metabolically generated from sulfate (Lee et al, 2012). However, there is a limited information about other redox active metabolic by‐product of conductive iron sulfide (FeS) produced by SRB in the context of anodic current generation. In this study, we establish that the biomineralized FeS significantly enhanced the anodic current generation in Desulfovibrio vulgaris Hildenborough, compared with that mediated by diffusive sulfate only. In a three electrode electrochemical cell, chronoamperometry with indium tin‐doped oxide electrodes (ITO) poised at +0.4 V (vs SHE) in the presence of lactate and sulfate showed that the presence of ferrous ion caused twice more anodic current than that in the absence of the iron (Fig 1). Linear Sweep Voltammetry (LSV), Scanning Electron Microscopy (SEM) and X‐ray Photoelectron Spectroscopy (XPS) confirmed that the aggregation formation of cells with FeS and FeS2 particles on the surface of the ITO electrode. These iron sulfur precipitates were more oxidized on the anode surfaces once lactate was depleted as electron source. Overall, the experimental data suggests that biosynthesized FeS mediates the electron transport from D. vulgaris Hildenborough to the electrode surface. Our proposed mechanism for anodic current generation by Desulfovibrio vulgaris Hildenborough is shown in Figure 2. Given microbial capability of FeS biosynthesis is general among SRB, the FeS‐mediated mechanism may dominate the anodic current generation of SRB in MFCs.

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  • In-Situ Biosynthetically Produced Iron Sulfide Nanocluster by Sulfate reducing bacteria Enhanced Anodic Current Generation in Microbial Fuel Cells

    岡本 章玄, ムルガン ムラリダハラン, 増田 卓也, Dae Sung Lee, ミラン ワヒード

    5th International Water Industry Conference 2019  2019.9 

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    Language：English   Presentation type：Oral presentation (general)  

    A microbial fuel cell (MFC) is a device that converts chemical energy to electrical energy with the aid of microorganisms. In MFCs, current generation by sulfate reducing bacteria (SRB) is known to produce by the anodic oxidation of sulfide which is metabolically generated from sulfate (Lee et al, 2012). However, there is a limited information about other redox active metabolic by‐product of conductive iron sulfide (FeS) produced by SRB in the context of anodic current generation. In this study, we establish that the biomineralized FeS significantly enhanced the anodic current generation in Desulfovibrio vulgaris Hildenborough, compared with that mediated by diffusive sulfate only. In a three electrode electrochemical cell, chronoamperometry with indium tin‐doped oxide electrodes (ITO) poised at +0.4 V (vs SHE) in the presence of lactate and sulfate showed that the presence of ferrous ion caused twice more anodic current than that in the absence of the iron (Fig 1). Linear Sweep Voltammetry (LSV), Scanning Electron Microscopy (SEM) and X‐ray Photoelectron Spectroscopy (XPS) confirmed that the aggregation formation of cells with FeS and FeS2 particles on the surface of the ITO electrode. These iron sulfur precipitates were more oxidized on the anode surfaces once lactate was depleted as electron source. Overall, the experimental data suggests that biosynthesized FeS mediates the electron transport from D. vulgaris Hildenborough to the electrode surface. Our proposed mechanism for anodic current generation by Desulfovibrio vulgaris Hildenborough is shown in Figure 2. Given microbial capability of FeS biosynthesis is general among SRB, the FeS‐mediated mechanism may dominate the anodic current generation of SRB in MFCs.

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  • Good and bad living electrode catalysts: Interfacial electron transfer mechanisms between bacteria and electrodes

    岡本 章玄

    5th International Water Industry Conference 2019  2019.9 

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    Microbial electron transport, referred as extracellular electron transport (EET), has significant implications for wastewater treatment coupled with bioenergy production, and microbially influenced corrosion for iron pipelines. Transmembrane multi-heme c-type cytochrome (OM c-Cyt) complexes function in unison as a biological “electron conduit” to make electron transport across the outer membrane to the cell exterior in several genera of iron-reducing or -oxidizing bacteria (Fig. 1)[ D. J. Richardson, et al. 2012]. The electron conduction mechanism through the multiple heme cofactors to promote highly efficient electron transport remains unclear under in vivo condition. To understand and control these microbial processes, we study electron transport mechanisms through the transmembrane biological electric conduit and pioneering whole-cell physico-chemical methodology combined with molecular-biological approaches. In the presentation, history and basic concepts of EET will be introduced, and we will discuss about the role of proton transport associated with EET [A. Okamoto, et al. 2017], flexible heme alignment in OM c-Cyts [Y. Tokunou, et al. 2018], and our recent discovery of novel clade of OM c-Cyts from iron-corrosion bacteira [X. Deng, et al. 2018].

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  • 「健全性崩壊をもたらす微生物による視認不可腐食の分子生物・電気化学的診断及 び抑制技術の開発」

    岡本 章玄

    2020年10月20日第1回腐食分科会  2020.10 

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  • Extracellular Electron Transport Mechanisms by Sulfate-reducing Bacteria

    岡本 章玄

    2020KSBB Fall Meeting and International Symposium: Hybrid Conference  2020.10 

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    Extracellular Electron Transport Mechanisms by Sulfate-reducing Bacteria

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  • Iron Corrosive Sulfate Reducing Bacteria Uptake Extracellular Electrons Via Outer Membrane C-Type Cytochromes

    OKAMOTO, Akihiro, Deng Xiao, HASHIMOTO, Kazuhito

    Pacific Rim meeting on electrochemical and solid-state science  2016.10 

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    Iron Corrosive Sulfate Reducing Bacteria Uptake Extracellular Electrons Via Outer Membrane C-Type Cytochromes

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Research Projects

  • Development of an innovative treatment device using electrosterilization for wounds with infection

    Grant number：24K22227  2024.6 - 2026.3

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research  Grant-in-Aid for Challenging Research (Exploratory)

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    Grant amount：\6370000 （ Direct Cost: \4900000 、 Indirect Cost：\1470000 ）

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  • 低張浸透圧バイオフィルム殺菌技術を用いた医療機器開発と国際展開

    2024

    科学技術振興機構  産学が連携した研究開発成果の展開 大学発新産業創出基金事業 ディープテック・スタートアップ国際展開プログラム(D-Global) 

    岡本 章玄

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    新原理の低張浸透圧バイオフィルム殺菌技術を活用して、整形外科インプラント感染および創傷感染に対する治療機器を開発し、展開するグローバルスタートアップの設立を目指す。

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    J-GLOBAL

  • 鉄腐食細菌に殺菌剤耐性を与えるレドックス二次代謝物のデータ駆動探索法の開発

    Grant number：22KK0242  2023 - 2025

    日本学術振興会  科学研究費助成事業  国際共同研究加速基金(国際共同研究強化(A))

    岡本 章玄

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    Grant amount：\15470000 （ Direct Cost: \11900000 、 Indirect Cost：\3570000 ）

    微生物鉄腐食の革新的オンサイトリスク評価技術の創生へ向けて、基課題では主要な原因である硫酸還元細菌（SRB）の鉄から電子を引き抜く反応を加速する可溶性レドックス分子のデータ駆動型探索を電気化学計測に基づいて進めている。薬剤耐性遺伝子群の発現がレドックス特性を有する二次代謝物によって制御される機構は多様な細菌で確認されているが、微生物鉄腐食の分野においては報告がない。申請者らは、殺菌剤を定期的に添加していても微生物腐食による事故が絶えない原因として、二次代謝物による薬剤耐性の活性化機構を着想した。本国際共同研究では、二次代謝物と薬剤感受性の研究において世界をリードしているDianne Newman教授と共に、SRBの殺菌剤耐性獲得とレドックス分子の関係に迫る。これまでに具体的には、薬剤耐性を活性化する分子を探索する電気化学手法の開発をモデル細菌系を用いて行ってきた。薬剤耐性タンパク質の活性を電気化学的に評価することが可能になっており、この手法を今後はSRBを含む細菌系へ適用していく予定である。また、Dianne Newman研究室において行っている緑膿菌の電気化学培養と、岡本らのハイスループット系の技術を組み合わせた新しい共同研究が展開している。この研究によって電気化学培養時に興味深い薬剤耐性を有することが新たにわかってきており、NIHの予算申請へ現在準備中である。また、本内容に関しては、すでに論文を投稿済みであり、二報目の論文投稿へ向けて準備を進めている。

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  • 微生物鉄腐食を加速する可溶性レドックス分子のデータ駆動型研究

    Grant number：23K23532  2022.4 - 2025.3

    日本学術振興会  科学研究費助成事業  基盤研究(B)

    岡本 章玄, 今村 岳, Deng Xiao

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    Grant amount：\17420000 （ Direct Cost: \13400000 、 Indirect Cost：\4020000 ）

    硫酸還元菌は、鉄パイプライン等の嫌気環境で鉄腐食を引き起こし、甚大な経済損失と事故を引き起こしている。暗所や視認困難な場所で起きる嫌気バイオ腐食を防ぐためには現場の採水試料を用いた加速試験法の開発が鍵となる。申請者らはこれまでに、電気化学と分子生物学手法を用いて硫酸還元菌が固体から電子を直接引き抜く「Extracellular Electron Uptake (EEU)」が鉄腐食速度と高い相関性を示すことを明らかにした。本研究では、EEUに基づくバイオ鉄腐食の速度論的理解・制御を通して、バイオ腐食細菌の加速試験開発へとつなげる。申請者らが独自に開発したハイスループット電気化学測定系にデータ駆動科学（ベイズ最適化）の手法を組み合わせることで、硫酸還元菌によるEEUを大幅加速する電子ミディエーターの分子構造を網羅的に探索・特定する。本年度は、保有分子のデータを取得し、ベイズ最適化を適用することで、電流値を大幅に加速する小分子を購入可能な分子群から特定するパイプラインを構築した。モデル細菌において、電流値を大幅に増大する分子群を比較したところ、レドックス電位のみならず膜透過性が重要な鍵であることが初めて見出された。また、このパイプラインを用いてSRBのEEU速度に影響を与える小分子を特定する実験を進めている。最も高い特性を示した分子に対して、今後、鉄腐食速度を確認し、有意な加速が可能か検証する。今年度、２報の論文を投稿しており、現在２報の論文を準備中である。

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  • 微生物鉄腐食を加速する可溶性レドックス分子のデータ駆動型研究

    Grant number：22H02265  2022.4 - 2025.3

    日本学術振興会  科学研究費助成事業  基盤研究(B)

    岡本 章玄, 今村 岳, Deng Xiao

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    Grant amount：\17420000 （ Direct Cost: \13400000 、 Indirect Cost：\4020000 ）

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  • 発電機能を持つ歯周病細菌におけると鉄イオン排出機構に関する研究

    Grant number：21F21412  2021.11 - 2024.3

    日本学術振興会  科学研究費助成事業  特別研究員奨励費

    岡本 章玄, NARADASU DIVYA

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    Grant amount：\2300000 （ Direct Cost: \2300000 ）

    Bacterial outer membrane vesicles (OMVs) are spherical lipid bilayer nanostructures released by bacteria that facilitate oral biofilm formation via cellular aggregation and intercellular communication. Recent studies have revealed that Capnocytophaga ochracea is one of the dominant members of oral biofilms; however, their potential for OMV production has yet to be investigated. This study demonstrated the biogenesis of OMVs in C. ochracea associated with the concentration of unsaturated fatty acids of phosphatidylinositol (PI) and characterized the size and protein profile of OMVs produced at growth phases. Transmission electron microscopy showed isolated spherical structures from cells stained with heavy metals, indicating the production of OMVs with a size ranging from 25 to 100 nm. Lipidome analysis revealed the presence of phosphatidic acid, phosphatidylethanolamine, phosphatidylcholine, and PI as the main lipids. Some unsaturated fatty acids of PI were present specifically in OMV and little in the outer membrane, suggesting that OMVs are generated from a specific region of the membrane through blebbing rather than a random process such as cell lysis. Furthermore, the lack of similar PI accumulation in the OMV of Porphyromonas gingivalis suggests that C. ochracea has a different biogenesis mechanism. The present study provides a basis for further understanding the roles of C. ochracea OMVs in oral biofilms as well as systemic diseases that C. ochracea involves.

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  • Electrochemical acceleration of ammonium biosynthesis from nitrogen gas

    Grant number：20F20105  2020.11 - 2023.3

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research  Grant-in-Aid for JSPS Fellows

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    Grant amount：\2300000 （ Direct Cost: \2300000 ）

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  • ハイスループット電気化学培養法による電気細菌の同時複数単離法の開発

    Grant number：20H05590  2020.4 - 2022.3

    日本学術振興会  科学研究費助成事業  新学術領域研究(研究領域提案型)

    岡本 章玄

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    Grant amount：\8320000 （ Direct Cost: \6400000 、 Indirect Cost：\1920000 ）

    電気細菌や発電細菌と呼ばれる細胞外固体と直接電子のやり取り「細胞外電子移動(Extracellular Electron Transport, EET)」を行い代謝する細菌が特に熱水噴出孔などの深海生態系において注目されており、電気培養によって未分離の細菌を集積・単離する試みが盛んに行われている。しかし、電気化学測定系の制約 から単離効率が極めて低いという長年の課題があった。本研究では、フローサイトメトリーによって1細菌に分離してから電極培養するハイスループット電気微生物培養法の開発を行なった。これまでに、環境サンプルから電極培養で環境中から電気細菌を単離することに成功したが、９６ウェルプレート上で電流生成が観測されるウェル数が少ないという問題点があった。各ウェルの中央に配置されている電極上に細菌が到達しない場合に電気培養が進まないことが考えられたため、電気細菌表面に選択的に吸着する磁性ナノ粒子を開発した（特許出願済み）。ナノ粒子を用いることで、環境中の電気細菌が濃縮され高い電流生成が示されることを確認した。さらに、ナノ粒子が吸着した後にも細菌が電流生成を行うことが確認できたため、電極培養へ直接アプライできることが示された。今後は、磁性ナノ粒子を用いて電気細菌を濃縮した後に、電極上に磁力で誘導、電気培養を行うことで１細胞電極培養の成功率を高める予定である。加えて、単離した細菌株の新種提唱の論文と電気化学解析を行なった論文の２報を準備中である。

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  • 酸化還元特性を持つ膜小胞によるバイオフィルム活性の制御

    Grant number：19F19406  2019.11 - 2022.3

    日本学術振興会  科学研究費助成事業  特別研究員奨励費

    岡本 章玄, MIRAN WAHEED

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    Grant amount：\2300000 （ Direct Cost: \2300000 ）

    The electrochemical reactor systems currently used for current production and drug testing involve relatively large volumes, making these systems infeasible for high-throughput screening of potential antimicrobials. We used screen-printed electrodes or multi-well electrode systems that require minimum amounts of sample and antimicrobials. Such systems that exploit the electrogenic activity of pathogens could fast-track the discovery of antibiofilm drugs, as a large library of compounds could be rapidly screened. This concept could serve as a generally applicable technology for evaluating the efficacy of antimicrobials, as well as the selection of appropriate drugs or treatment regimens. Our works extended the boundaries of EET field to other niches such as human pathogens. The orthologues of the identified EET genes in human pathogens are present in hundreds of species, thus EET activity likely occurred in an evolutionarily diverse subset of bacteria. Consequently, our research can help screen the effects of antimicrobials on biofilm activity by employing the current producing capability in wide range of electroactive pathogens.

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  • Control of extracellular Electron Transport to Enhance the Rate of Fermentation-hybrid Respiration

    Grant number：17H04969  2017.4 - 2021.3

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research  Grant-in-Aid for Young Scientists (A)

    OKAMOTO Akihiro

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    Grant amount：\23920000 （ Direct Cost: \18400000 、 Indirect Cost：\5520000 ）

    We conducted a multifaceted analysis of "extracellular proton efflux", which we found as a key factor in the fast drive of fermentation metabolism on electrodes by the electrophilic bacterium Shewanella. We clarified the mechanism and achieved control of the electron transfer rate. In addition, we have realized a fast metabolic reaction by electrodes in a model bacteria of bioprocess (Escherichia coli). Our achievement provide a novel strategy to speed up the production of microbial substances and materials such as drugs and bioplastics.

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  • Periplasmic proton accumulation mechanism in alkaliphilic bacteria capable of extracellular electron transport

    Grant number：26810085  2014.4 - 2016.3

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research  Grant-in-Aid for Young Scientists (B)

    okamoto akihiro

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    Grant amount：\4160000 （ Direct Cost: \3200000 、 Indirect Cost：\960000 ）

    Alkaliphilic gram-positive microbe capable of extracellular electron transport (EET) was enriched and isolated from The Cedars spring at pH 12, using on-site microbial fuel cell system with anode connected with air cathode. Also, we developed a method to monitor the periplasmic proton concentration using the EET-capable microbe.

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  • in-vivo微生物電気化学を使った好アルカリ細菌のプロトン集積機構の研究

    Grant number：25888006  2013.8 - 2015.3

    日本学術振興会  科学研究費助成事業  研究活動スタート支援

    岡本 章玄

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    Grant amount：\2730000 （ Direct Cost: \2100000 、 Indirect Cost：\630000 ）

    プロトン（H+）は電子移動とカップルするため、その局在濃度は人工光合成や燃料電池の触媒効率に直接作用する。本研究の目的は、極限環境微生物に見られる細胞外H+濃度に逆相関して細胞膜上により多くH+を集積する機構の解明である。極限菌の一種である好アルカリ菌は、細胞内部に較べて膜外のpHがより高い条件において、膜上タンパク質に電子を貯め込むことでH+を局在化させ、ATPを合成すると提案されている。しかし、呼吸鎖における電荷の局在性を確かめるには、律速電子移動過程の特定が不可欠となるが、既存の単独・単離タンパク系での検討は極めて難しい。本研究では、電流生成菌を生きたまま電気化学システムに適用する「微生物電気化学」を用いて、申請者が発見した初となる好アルカリ電流生成菌と電極の界面電子移動と細胞内ATP濃度をin-vivo同時追跡することで、高アルカリ条件に逆相関するH+局在機構に迫ることを目指す。本年度は、（１）好アルカリ電流生成菌の連続希釈法による単離、（２）ゲノム塩基配列の決定、解析を行うことを研究計画として掲げていたが、申請者が米国研究機関で集積した微生物が全く増殖しなくなり再び菌体の採取から行うこととなった。そこで、再現性を確認する意味も込めてサンフランシスコ山中のpH１２の極限環境に再び電極を設置し、採集したサンプルを米国実験室で電極培養すると以前観測されたように微生物の代謝に由来する電流値の増加が確認された。電極を日本に輸送し、立ち上げた嫌気ボックス内で電極培養実験を行なうと、最初は輸送中の酸素混入によるダメージからから電流値がほとんど観測されなかったが、徐々に電流値の上昇が観測された。現在、単離に向けて微生物を集積中である。

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  • Pioneer the Physical Chemistry of Biological Electron Transfer based on Bacterial Extracellular Electron Transport

    Grant number：24000010  2012 - 2016

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research  Grant-in-Aid for Specially Promoted Research

    HASHIMOTO Kazuhito, NAKAMURA Ryuhei, NAKANISHI Shuji, ISHIHARA Kazuhiko, TAJIMA Keisuke, OKAMOTO Akihiro, KAMIYA Kazuhide

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    Grant amount：\512850000 （ Direct Cost: \394500000 、 Indirect Cost：\118350000 ）

    The molecular mechanism of extracellular electron transfer (EET) was clarified through the direct observation of the dynamics, leading to the development of the methodologies for reversible regulation and collective activation of cellular metabolisms. It was also revealed that microorganisms with EET ability are widely distributed in natural environments. Furthermore, we successfully applied the concept of the EET to mammalian cells that do not possess EET ability by developing cytocompatible electron mediators. Based on the systematic understandings of the EET obtained through the present study, novel methodologies and perspectives were provided to various fields, including measurement/regulation of circadian clocks and cancer cells, and proposal of new ecosystem supported by electricity.

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