BACTERIAL SURVIVAL, GROWTH AND PHYSIOLOGY UNDER PERCHLORATE EXPOSURE: IMPLICATIONS FOR LIFE IN MARTIAN BRINES

Abstract

With the development of space exploration, one of the main goals of astrobiology is to avoid contaminating other planets with terrestrial organisms. For this, the tolerance of microorganisms to space and extraterrestrial conditions is thoroughly studied. Here, we evaluated the resistance of two bacterial strains isolated from extreme environments, Buttiauxella sp. MASE-IM-9 and Salinisphaera shabanensis, to a stress factor specific to the Martian surface: the presence of perchlorate ions. For this, both strains were exposed or grown in the presence of various types of perchlorate salts. Additionally, the proteomic response of Buttiauxella sp. MASE-IM-9 to sodium and magnesium perchlorates was investigated. Results showed that both strains could survive and grow in Mars-relevant concentrations of perchlorates. S. shabanensis, a halophilic bacterium from deep-sea brines, had a higher tolerance to perchlorates. The formation of chains that was previously observed on Buttiauxella sp. MASE-IM-9 in anoxic conditions was not seen in oxic conditions. Proteome analysis showed that perchlorates induced the usual response to oxidative and osmotic stress, but also led to an upregulation of CusF, a protein involved in copper efflux. We proposed that this mechanism could be a strategy to protect Fe-S cluster enzymes from an accumulation of copper resulting from a downregulation of methionine biosynthesis. Altogether, these findings increase our knowledge of bacterial growth and physiology in perchlorate-rich environments, with implications for astrobiology but also for perchlorate bioremediation on Earth.