Publisher：Cold Spring Harbor Laboratory  

Abstract

The lipid world hypothesis proposes that both intracellular componentsandthe chemical composition of the membrane compartment carry heritable information that contributes to protocellular fitness. However, there are few experimental demonstrations of membrane compositional selection and no study has shown that phospholipids—the primary membrane components of modern cells—can support selection of this type. As lipid compartments generally grow in size before fission, faster-growing compartments should enjoy a selective advantage that favors both the membrane itself and the contents it hosts. When situated in icy environments undergoing cycles of freezing and thawing (F/T), we found that the growth of phospholipid vesicles depends on their phospholipid composition: Vesicles with more unsaturated bonds in the acyl chain showed higher growth efficiency. When vesicles composed of lipids with either one or two unsaturated bonds were mixed and subjected to F/T cycles, a selective enrichment of the lipid with two unsaturated bonds was observed. Moreover, selection acting on lipid composition was propagated to the encapsulated genetic material, which was also enriched while selectively neutral. We conclude that phospholipid composition can be a direct target of selection for grown vesicles under an icy environment leading to indirect but concurrent enrichment of compartmentalized genetic molecules.

DOI： 10.1101/2025.04.16.648126

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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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Authorship：Lead author   Publishing type：Research paper (scientific journal)   Publisher：Wiley  

The creation of large information molecules may have played an essential role in the origins of life. In this study, we conducted slow freeze‐thaw (F/T) experiments to test the possibility of enhanced hybridization between the complementary sticky ends attached to kilobase‐sized DNA fragments at sub‐nanomolar concentrations. DNA fragments of 2‐ and 3‐kilobase pairs (kbp) with 50‐base complementary sticky ends that can form 5 kbp‐sized hybridization products were mixed. While simple incubation provided little hybridization product, significantly effective hybridization was observed after freezing and thawing at a controlled time rate (<0.3 K min⁻¹), even with small DNA concentrations (<1 nM). Furthermore, slow thawing had a more effect on hybridization than slow freezing. The reaction efficiency was reduced by rapid thawing instead of slow thawing, suggesting that the eutectic phase concentration played an important role in hybridization. A slow F/T cycle was effective even for the hybridization reaction between two 10 kbp DNA fragments, which yielded a 20 kbp product at sub‐nanomolar concentrations. Repeating the slow F/T cycle significantly improved the reaction efficiency. The possible role of the F/T cycles in early Earth environments is discussed here.

DOI： 10.1002/syst.202400025

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

DOI： 10.1029/2023gl103015

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Mineralogical Society of America  

Abstract

Clay minerals are widely distributed on the surface of Earth, Mars, and Ceres in the solar systems. Among numerous clay minerals, smectites can record the history of the environment through the exchange of interlayer cations with those in water or through redox reactions with the atmosphere. Therefore, characterization of chemical compositions and crystal structures of smectites is crucial for revealing the paleoenvironment. For instance, the crystal structure within octahedral sheets of iron-bearing smectites changes to trioctahedral sheets under reduced or dioctahedral sheets under oxidizing conditions. Orbital infrared and X-ray diffraction (XRD) analyses by Mars orbiters/rovers revealed the presence of (Fe,Mg)-smectites on the surface of Mars; however, it has been difficult to characterize the properties of these (Fe,Mg)-smectites, which are rare on the surface of Earth. In this study, we synthesized ferrian (ferric ion-rich) and ferrous (ferrous ion-rich) (Fe,Mg)-saponite and revealed the effect of valence states and iron contents on the crystal structures. These saponites were synthesized using a hydrothermal method under reduced conditions. The crystal structures and valence states of iron were analyzed by XRD, Fourier-transform infrared spectroscopy, transmission electron microscopy, Mössbauer spectroscopy, and X-ray absorption near edge measurements. The synthesized clays were trioctahedral swelling clays and were identified as saponites. The valence state of iron in these synthesized saponites is altered by oxygen and a reducing agent in water; however, the trioctahedral structures are maintained under both oxidizing and reduced conditions, following a reversible reaction. This mechanism can be interpreted by the desorption and adsorption of hydrogen in the hydroxyls of the octahedral sheets of the smectite layers. The maximum basal spacing of the (02l) lattice plane in the octahedral sheets was defined by compiling various smectite data. When the basal spacing of (02l) is larger than the maximum in dioctahedral smectites, smectite can be identified as trioctahedral smectite. The redox state of iron in the octahedral sheet cannot be determined from the basal spacing of (02l). We revealed that the iron content in the trioctahedral sheet has a linear relationship with lattice parameter b. This provides a method to estimate the iron content in saponite from XRD data. The XRD profiles of smectites found at the Yellowknife Bay on Mars can be explained only by trioctahedral smectites, and the iron content in the octahedral sheet is roughly estimated to be 0.5–1.7 in a half-unit cell. These results indicate that the presence of (Fe,Mg)-saponite implies a reduced environment during the formation and that this iron-bearing saponite has both oxidation and reduction capabilities depending on the environment.

DOI： 10.2138/am-2022-8231

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