Investigation of the Growth and Survival of Bacteria from Mars Analog Environments When Exposed to Mars-like Conditions

The purpose of this study was to test the growth of organisms from terrestrial Mars analog environments when exposed to Mars-like conditions. First, the growth of over 75 bacterial strains from the Atacama Desert was tested in the presence of high concentrations (50 mM to 1 M ) of three different perchlorate salts – NaClO4 ∙ H2O, Mg(ClO4)2 ∙ 6 H2O, and Ca(ClO4)2 ∙ 4 H2O found on the Martian surface. Strains tested belonged to a variety of genera such as Blastococcus, Microvirga, Geodermatophilus, and Kocuria. Control strains used for comparison included a number of Gram-positive and Gram-negative bacteria, many that were isolated from other extreme environments. In general, a decrease in bacterial growth was observed as perchlorate concentration increased. Atacama Desert isolates, especially Blastococcus and Kocuria sp., grew at higher perchlorate concentrations than any of the bacterial control strains. It was noted that Gram-positive organisms are capable of growing at higher perchlorate concentrations than Gram-negative organisms. Results from these tests have applications in research involving bacterial perchlorate tolerance, as well as the search for life on Mars. Secondly, the diversity of ionizing-radiation resistant bacteria in permafrost soil was studied by exposing two soil samples from the Canadian High Arctic to various doses of gamma radiation. Samples were exposed to 0 (unirradiated), 1, 2, 3, and 11.1 kGy doses and subsequently dilution plated onto a variety of nutrient media including marine agar, R2 agar, 1/100 PCA, and 1/10 PCA. Cfu ranged from 1.5 x 105 to 2.3 x 105 for unirradiated samples and 3.0 x 102 to 1.8 x 103 for samples exposed to 11 kGy. Colonies were selected from irradiated samples and 16S rRNA gene sequencing was used to identify the isolates as belonging to a number of genera including Hymenobacter, Pontibacter, Arthrobacter, Salinibacterium, and Paenibacillus. Phylogenetic analysis showed that nine strains were related to species of the genus Hymenobacter, and these were chosen for further characterization. This study identifies radiation resistant, psychrotolerant bacteria from permafrost and demonstrates the use of this selective technique to isolate them from the total bacterial community.

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