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Observations of trace methane (CH 4 ) in the Martian atmosphere are significant to the astrobiology community given the overwhelming contribution of biological methanogenesis to atmospheric CH 4  on Earth. Previous studies have shown that methanogenic  Archaea  can generate CH 4  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 CH 4  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 H 2  with perchlorate reduction, which we propose is catalyzed by up-regulated molybdenum-containing enzymes and maintained by siphoning diffused H 2  from energy-conserving hydrogenases. Methanogenesis regulatory patterns suggest Mars’ freezing temperatures alone pose greater constraints to CH 4  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 CH 4 .

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