Perchlorate-Coupled Carbon Monoxide (CO) Oxidation: Evidence for a Plausible Microbe-Mediated Reaction in Martian Brines

Abstract

The presence of hydrated salts on Mars indicates that some regions of its surface might be habitable if suitable metabolizable substrates are available. However, several lines of evidence have shown that Mars’ regolith contains only trace levels of the organic matter needed to support heterotrophic microbes. Due to the scarcity of organic carbon, carbon monoxide (CO) at a concentration of about 700 parts per million (about 0.4 Pa) might be the single most abundant readily available substrate that could support near-surface bacterial activity. Although a variety of electron acceptors can be coupled to CO oxidation, perchlorate is likely the most abundant potential oxidant in Mars’ brines. Whether perchlorate, a potent chaotrope, can support microbial CO oxidation has not been previously documented. We report here the first evidence for perchlorate-coupled CO oxidation based on assays with two distinct euryarchaeal extreme halophiles. CO oxidation occurred readily in 3.8 M NaCl brines with perchlorate concentrations from 0.01 to 1 M. Both isolates were able to couple CO with perchlorate or chlorate under anaerobic conditions with or without nitrate as an inducer for nitrate reductase, which serves as a perchlorate reductase in extreme halophiles. In the presence of perchlorate, CO concentrations were reduced to levels well below those found in Mars’ atmosphere. This indicates that CO could contribute to the survival of microbial populations in hydrated salt formations or brines if water activities are suitably permissive.

Halobacterium bonnevillei sp. nov., Halobaculum saliterrae sp. nov. and Halovenus carboxidivorans sp. nov., three novel carbon monoxide-oxidizing Halobacteria from saline crusts and soils

“…All grew aerobically or weakly under anoxic conditions with nitrate and some cells exhibited motility in early exponential phase under oxic conditions. PCN9 T and WSA2 T were also capable of reducing perchlorate to chlorite under anoxic conditions as well as oxidizing carbon monoxide as described by Myers King and [8]. Strain WSH3 T was also shown to be capable of carbon monoxide oxidation under aerobic conditions (Fig.…”

“…Globally, approximately 10 % of annual CO emissions are consumed by microbial species in soils, with the capacity haloarchaeal isolates to oxidize CO only recently discovered [5–7]. Several isolates obtained from the Bonneville Salt Flats (BSFs; Utah, USA) that contain these genes have been shown to couple CO oxidation to perchlorate reduction in addition to molecular oxygen and nitrate reduction [8, 9].…”

Discrete Community Assemblages Within Hypersaline Paleolake Sediments of Pilot Valley, Utah

“…303 304Microbial diversity of Pilot Valley compared to other Bonneville Basin remnants 305Relative to aquatic environments, hypersaline soils and sediments like those in the 306Bonneville Basin have been neglected by microbiologists. For example, while studies of the 307 microbial ecology of the Great Salt Lake began withPost (1977) and continue today, microbial 308 diversity in other Bonneville Basin remnants remains largely unknown(Kjeldsen et al, 2007 ; 309 Page 15 of 39 of interest or solely on the archaeal domain(Myers & King, 2017 ;Boogaerts, 2015). Further, 312…”

Carbon monoxide dehydrogenases enhance bacterial survival by oxidising atmospheric CO

“…In soils, the oxidation of atmospheric CO may be of similar importance to atmospheric H 2 ; this is suggested by the strength of the soil sinks for these gases [1, 85], the abundance of coxL and hhyL genes in soil metagenomes, and the distribution of these genes in the genomes of soil bacteria [86]. Atmospheric CO may be especially important for sustaining communities in highly oligotrophic soils, as indicated by previous studies in polar deserts [51], volcanic deposits [60, 62, 87], and salt flats [33, 88, 89]. Further work is now needed to understand which microorganisms mediate consumption of atmospheric CO in situ and how their activity is controlled by physicochemical factors.…”