Publishing type：Research paper (scientific journal)  

DOI： 10.1021/acsearthspacechem.4c00314

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Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

Circumneutral iron-rich hot springs may represent analogues of Neoarchean to Paleoproterozoic oceans of early Earth, potentially providing windows into ancient microbial ecology. Here we sampled five Japanese hot springs to gain insights into functional processes and taxonomic diversity in these analog environments. Amplicon and metagenomic sequencing confirm a hypothesis where taxonomy is distinct between sites and linked to the geochemical setting. Metabolic functions shared among the springs include carbon fixation via the reductive pentose phosphate cycle, nitrogen fixation, and dissimilatory iron oxidation/reduction. Among the sites, Kowakubi was unique in that it was dominated by Hydrogenophilaceae, a group known for performing hydrogen oxidation, motivating a hypothesis that H2 as an electron donor may shape community composition even in the presence of abundant ferrous iron. Evidence for nitrogen cycling across the springs included N2 fixation, dissimilatory nitrate reduction to ammonia (DNRA), and denitrification. The low-salinity springs Furutobe and OHK lacked evidence for ammonium oxidation by ammonia monooxygenase, but evidence for complete nitrification existed at Kowakubi, Jinata, and Tsubakiyama. In most sites, the microaerophilic iron-oxidizing bacteria from the Zetaproteobacteria or Gammaproteobacteria classes had higher relative abundances than Cyanobacteria. Microaerophilic iron oxidizers may outcompete abiotic Fe oxidation, while being fueled by oxy-phototrophic Cyanobacteria. Our data provide a foundation for considering which factors may have controlled productivity and elemental cycling as Earth's oceans became oxygenated at the onset of the Great Oxidation Event.

DOI： 10.1264/jsme2.ME24067

PubMed

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Publisher：arXiv  

We derive a single-cell level understanding of metabolism in an isogenic cyanobacterial population by integrating secondary ion mass spectrometry (SIMS) derived multi-isotope uptake measurements of Synechocystis sp. PCC6803 with a statistical inference protocol based on Liebig's law of the minimum, the maximum entropy principle, and constraint-based modeling. We find the population is structured in two metabolically distinct clusters: cells optimizing carbon yield while excessively turning over nitrogen, and cells which act reciprocally, optimizing nitrogen yield and excessively turning over carbon. This partition enables partial heterotrophy within the population via metabolic exchange, likely in the form of organic acids. Exchange increases the feasible metabolic space, and mixotrophic cells achieve the fastest growth rates. Metabolic flux analysis at the single-cell level reveals heterogeneity in carbon fixation rates, Rubisco specificity, and nitrogen assimilation. Our results provide a necessary foundation for understanding how population level phenotypes arise from the collective contributions of distinct individuals.

DOI： 10.48550/ARXIV.2506.05916

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Publishing type：Research paper (scientific journal)   Publisher：American Geophysical Union (AGU)  

Abstract

Molecular hydrogen is an important gas species for understanding the early Martian climate and redox chemistry. Through ancient aqueous alterations of crustal rocks, ferrous (Fe(II)) saponite formed abundantly on Mars. Subsequent intrusions of hydrothermal fluids may have resulted in a chemical reaction between the dissolved volatiles and the nearby rocks. Here we propose a new H₂ generating reaction between ferrous saponite and H₂S‐containing fluids, which is possible on early Mars. A series of hydrothermal experiments at a relatively low temperature of 90°C were performed under anoxic conditions using synthesized ferrous saponite to compare the resulting H₂ concentration among various gas and fluid compositions. Based on the relationship with the existence of H₂S, reaction time, fluid pH, dissolved iron concentration, and amount of minerals, we found that high levels of H₂ (∼0.1 mmol/g ferrous saponite) were generated in the presence of H₂S most rapidly in moderate pH conditions. Our microscopic chemical analysis of mineral phases suggested that ferrous saponite served as both the iron source of pyrite precipitation and the electron source to form H₂. Our results suggest that intrusions of H₂S‐containing fluids into the saponite‐containing crust of Mars would generate H₂, which could potentially provide locally concentrated chemical energy for chemoautotrophic life.

DOI： 10.1029/2024je008538

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Publishing type：Research paper (scientific journal)  

DOI： 10.3847/2041-8213/ad74da

Scopus

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Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

DOI： 10.1038/s41467-024-52332-3

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Other Link： https://www.nature.com/articles/s41467-024-52332-3

Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

An unresolved question in the origin and evolution of life is whether a continuous path from geochemical precursors to the majority of molecules in the biosphere can be reconstructed from modern-day biochemistry. Here we identified a feasible path by simulating the evolution of biosphere-scale metabolism, using only known biochemical reactions and models of primitive coenzymes. We find that purine synthesis constitutes a bottleneck for metabolic expansion, which can be alleviated by non-autocatalytic phosphoryl coupling agents. Early phases of the expansion are enriched with enzymes that are metal dependent and structurally symmetric, supporting models of early biochemical evolution. This expansion trajectory suggests distinct hypotheses regarding the tempo, mode and timing of metabolic pathway evolution, including a late appearance of methane metabolisms and oxygenic photosynthesis consistent with the geochemical record. The concordance between biological and geological analyses suggests that this trajectory provides a plausible evolutionary history for the vast majority of core biochemistry.

DOI： 10.1038/s41559-024-02361-4

PubMed

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1186/s40645-023-00603-w

Scopus

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Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.isci.2024.111088

Scopus

PubMed

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