Perchlorate and halophilic prokaryotes: implications for possible halophilic life on Mars

Abstract

In view of the finding of perchlorate among the salts detected by the Phoenix Lander on Mars, we investigated the relationships of halophilic heterotrophic microorganisms (archaea of the family Halobacteriaceae and the bacterium Halomonas elongata) toward perchlorate. All strains tested grew well in NaCl-based media containing 0.4 M perchlorate, but at the highest perchlorate concentrations, tested cells were swollen or distorted. Some species (Haloferax mediterranei, Haloferax denitrificans, Haloferax gibbonsii, Haloarcula marismortui, Haloarcula vallismortis) could use perchlorate as an electron acceptor for anaerobic growth. Although perchlorate is highly oxidizing, its presence at a concentration of 0.2 M for up to 2 weeks did not negatively affect the ability of a yeast extract-based medium to support growth of the archaeon Halobacterium salinarum. These findings show that presence of perchlorate among the salts on Mars does not preclude the possibility of halophilic life. If indeed the liquid brines that may exist on Mars are inhabited by salt-requiring or salt-tolerant microorganisms similar to the halophiles on Earth, presence of perchlorate may even be stimulatory when it can serve as an electron acceptor for respiratory activity in the anaerobic Martian environment.

Carbon monoxide as a metabolic energy source for extremely halophilic microbes: Implications for microbial activity in Mars regolith

“…Perchlorate has been previously reported at somewhat higher levels for two locations on Mars' surface (49-51), but higher concentrations might not prove to be a serious constraint, because Oren et al (32) have reported tolerance of up to 0.4 M sodium perchlorate by several extreme halophiles. Indeed, in addition to tolerating perchlorate, some CO oxidizers might be able to use it as a respiratory electron acceptor.…”

“…Indeed, in addition to tolerating perchlorate, some CO oxidizers might be able to use it as a respiratory electron acceptor. Perchlorate reduction using organic substrates has been reported for several extremely halophilic euryarchaeotes (32,52), but A. ehrlichii MLHE-1 did not oxidize CO with perchlorate (Fig. S2) ), and an analogous process, perchlorate-dependent hydrogen oxidation, has been used for perchlorate bioremediation (53).…”

“…Although this might be true at a global scale, substantial activity could occur at more local scales, such as those of RSL. However, CO utilization has not been previously documented for terrestrial brines or soils experiencing water potential extremes that would characterize putative RSL brines, nor has CO oxidation been demonstrated for extreme halophiles, which have been posited as models for life on Mars (29)(30)(31)(32).…”

Anaerobic Metabolism in Haloferax Genus

“…In general terms, Haloferax growth under those microaerobic or even strict anaerobic conditions is possible because oxygen is replaced by other final electron acceptors such us nitrate, nitrite (Lledó, Martinez-Espinosa, Marhuenda-Egea & Bonete, 2004;Bonete et al, 2008;Nájera-Fernández, Zafrilla, Bonete & Martinez-Espinosa, 2012;Esclapez, Zafrilla, Martinez-Espinosa & Bonete, 2013) (per)chlorate (Oren, Elevi-Bardavid & Mana, 2014; Martínez-Espinosa, Richardson & Bonete, 2015), sulphur or sulphide (Elshahed et al, 2004), arsenate (Rascovan, Maldonado, Vazquez & Eugenia Farias, 2015), dimethyl sulfoxide (DMSO), trimethylamine N-oxide (TMAO) and fumarate (Oren & Trüper, 1990;Oren, 1991;Oren, 1999;Müller & DasSarma, 2005).…”

Growth of Bacillus pumilus and Halomonas halodurans in sulfates: prospects for life on Europa

“…The adaptive strategies for tolerance at high MgSO 4 concentrations were not explored, but the authors noticed some unexplained differences in the growth rate and stationary-phase maximum densities when their isolates were exposed to different sulfate salts. There are some reports about the substitution of NaCl with other salts (Oren et al, 2014), but very few in the context of exploring the possibilities of survival of terrestrial microorganisms in an Europan scenario.…”