Seminar Series: Andrew Schuerger, University of Florida

“Hypobarophile Bacteria Capable Of Growth Under Martian Conditions Of 7 mbar, 0 C, And CO2-enriched Anoxic Atmospheres”

Twenty-six strains of 22 bacterial species were tested for growth on trypticase soy agar (TSA) or sea-salt agar (SSA) under hypobaric, psychrophilic, and anoxic conditions applied singly or in combination.  As each factor was added to multi-parameter assays, the interactive stresses decreased the numbers of strains capable of growth, and in general, reduced the vigor of the strains observed to grow.  Only Serratia liquefaciens strain ATCC 27592 exhibited growth at 7 mbar, 0 C, and CO2-enriched anoxic atmospheres.  In order to discriminate between the effects of desiccation and hypobaria, vegetative cells of Bacillus subtilis strain 168 and Escherichia coli strain K12 were grown on TSA surfaces and simultaneously in liquid Luria-Bertani (LB) broth media.  Inhibition of growth under hypobaria for 168 and K12 decreased in similar ways for both TSA and LB assays as pressures were reduced from 100 to 25 mbar.  Results for 168 and K12 on TSA and LB are interpreted to indicate a direct low-pressure effect on microbial growth with both species, and do not support the hypothesis that desiccation alone on TSA was the cause of reduced growth at low pressures.  The growth of S. liquefaciens at 7 mbar, 0 C, and CO2-enriched anoxic atmospheres was surprising since S. liquefaciens is ecologically a generalist occurring in terrestrial plant, fish, animal, and food niches.  In contrast, two extremophiles tested in the assays, Deinococcus radiodurans strain R1 and Psychrobacter cryohalolentis strain K5, failed to grow under hypobaric (25 mbar; R1only), psychrophilic (0 C; R1 only), or anoxic (< 0.1% ppO2; both species) conditions.

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