SALT TOLERANCE OF BACTERIA FOUND IN WYOMING ROCK UNITS/SEDIMENTS

Aridity affects both biology and geology. Micro-organisms can survive in arid environments just as there is specific geology born out of arid environments. In this study, we determined the water availability requirements of microorganisms on surfaces of rocks from arid settings. The three samples used included the Jurassic Morrison (Jm), Cretaceous Thermopolis (Kt), and the Permian Goosegg (Pge). These samples were chosen because they were extractable representatives of Wyoming’s arid landscapes. The Jm and Kt came from Wyoming’s Bighorn Basin at structures Sheep and the Goosegg Anticline near Lovell, Wyoming. The Pge was collected from Seminoe State Park near Rawlins, Wyoming. Characterization of the samples by X-ray diffraction (XRD) revealed mineralogical similarities and differences between the samples. All included quartz and some form of sheet mineral as muscovite or illite. Kt and Pge included dolomite and calcite respectively. The characteristic mineral for Pge was ankerite, an iron-carbonate mineral. Water-extractable anions associated with the samples were determined by ion chromatography. Pge contained the highest Cl^- concentration and the lowest SO₄^2- concentration at 1.855 μmol/g and 0.350 μmol/g, respectively. Kt had the lowest Cl^- concentration at 0.254 μmol/g and an SO₄^2- concentration of 27.005 μmol/g. Jm had a Cl^- content of 1.145 μmol/g and the highest SO₄^2- content at 36.551 μmol/g. Cultureable organoheterotrophic bacteria associated with the samples were enumerated by plate counts using solid mineral media amended with either 1 or 10 g/L NaCl to differentiate between halophilic and non-halophilic microorganisms. Beginning with the low salt medium, Kt had the most growth at 5.7x10³ CFU/g , Jm had 8.5x10² CFU/g, and Pge had 1.4x10¹ CFU/g. The high salt medium had less growth, with Jm at 1.7x10¹ CFU/g and Pge at 10x10¹ CFU/g. Kt did not grow a countable number of CFUs. In comparing plate counts, we found that lower rock-associated Cl^- concentrations coincide with larger differences between growth on the low salt and high salt media. These results indicate that the chemistry of rock in arid regions influences the abundances of microorganisms associated with those rocks