Transcriptional response to prolonged perchlorate exposure in the methanogen Methanosarcina barkeri and implications for Martian habitability

Observations of trace methane (CH4) in the Martian atmosphere are significant to the astrobiology community given the overwhelming contribution of biological methanogenesis to atmospheric CH4 on Earth. Previous studies have shown that methanogenic Archaea can generate CH4 when incubated with perchlorates, highly oxidizing chaotropic salts which have been found across the Martian surface. However, the regulatory mechanisms behind this remain completely unexplored. In this study we performed comparative transcriptomics on the methanogen Methanosarcina barkeri, which was incubated at 30˚C and 0˚C with 10–20 mM calcium-, magnesium-, or sodium perchlorate. Consistent with prior studies, we observed decreased CH4 production and apparent perchlorate reduction, with the latter process proceeding by heretofore essentially unknown mechanisms. Transcriptomic responses of M. barkeri to perchlorates include up-regulation of osmoprotectant transporters and selection against redox-sensitive amino acids. Increased expression of methylamine methanogenesis genes suggest competition for H2 with perchlorate reduction, which we propose is catalyzed by up-regulated molybdenum-containing enzymes and maintained by siphoning diffused H2 from energy-conserving hydrogenases. Methanogenesis regulatory patterns suggest Mars’ freezing temperatures alone pose greater constraints to CH4 production than perchlorates. These findings increase our understanding of methanogen survival in extreme environments and confers continued consideration of a potential biological contribution to Martian CH4.

Regulatory responses of Methanosarcina barkeri to freezing temperatures and perchlorates: Transcriptomic insights into the potential for biological Martian methanogenesis

Observations of trace methane (CH4) in the Martian atmosphere are significant to the astrobiology community given the overwhelming contribution of biological methanogenesis to atmospheric CH4­ on Earth. Previous studies have shown that methanogenic Archaea can generate CH4 when incubated with perchlorates, highly oxidizing chaotropic salts which have been found across the Martian surface. However, the regulatory mechanisms behind this remain completely unexplored. In this study we performed comparative transcriptomics on the methanogen Methanosarcina barkeri, which was incubated at 30˚C and 0˚C with 10 mM calcium-, magnesium-, or sodium perchlorate. Consistent with prior studies, we observed decreased CH4 production and apparent perchlorate reduction, with the latter process proceeding by heretofore essentially unknown mechanisms. Transcriptomic responses of M. barkeri to perchlorates include up-regulation of osmoprotectant transporters and selection against redox-sensitive amino acids. Regulatory switches to methylamines for methanogenesis suggest competition for H2 with perchlorate reduction, which we propose is catalyzed by up-regulated molybdenum-containing enzymes and maintained by siphoning diffused H2 from energy-conserving hydrogenases. Methanogenesis regulatory patterns suggest Mars’ freezing temperatures alone pose greater constraints to CH4 production than perchlorates. These findings increase our understanding of potential methanogen survival beyond Earth and a biological contribution to Martian CH4.

A Bioinspired Molybdenum Catalyst for Aqueous Perchlorate Reduction

<p>The detection of perchlorate (ClO₄⁻) on and beyond Earth requires ClO₄⁻ reduction technologies to support water purification and space exploration. However, the reduction of ClO₄⁻ usually entails either harsh conditions or multi-component enzymatic processes. We developed a heterogeneous Mo−Pd/C catalyst from sodium molybdate to reduce aqueous ClO₄⁻ into Cl⁻ with 1 atm H₂ at room temperature. Upon hydrogenation by H₂/Pd, the reduced Mo oxide species and a bidentate nitrogen ligand (1:1 molar ratio) are transformed <i>in situ</i> into oligomeric Mo sites on the carbon support. The turnover number and frequency for oxygen atom transfer from ClO_x⁻ substrates reached 3850 and 165 h⁻¹ on each Mo site. This simple bioinspired design yielded a robust water-compatible catalyst for the removal and utilization of ClO₄⁻.</p>

A Bioinspired Molybdenum Catalyst for Aqueous Perchlorate Reduction

<p>The detection of perchlorate (ClO₄⁻) on and beyond Earth requires ClO₄⁻ reduction technologies to support water purification and space exploration. However, the reduction of ClO₄⁻ usually entails either harsh conditions or multi-component enzymatic processes. We developed a heterogeneous Mo−Pd/C catalyst from sodium molybdate to reduce aqueous ClO₄⁻ into Cl⁻ with 1 atm H₂ at room temperature. Upon hydrogenation by H₂/Pd, the reduced Mo oxide species and a bidentate nitrogen ligand (1:1 molar ratio) are transformed <i>in situ</i> into oligomeric Mo sites on the carbon support. The turnover number and frequency for oxygen atom transfer from ClO_x⁻ substrates reached 3850 and 165 h⁻¹ on each Mo site. This simple bioinspired design yielded a robust water-compatible catalyst for the removal and utilization of ClO₄⁻.</p>