N-141. Arsenic Oxidizing Chemoautotrophic Microorganisms from Geothermal Water and Sediments

E. García-Domínguez1, M. Bruno1, D. Nordstrom2, L. Young1;
1Rutgers Univ., New Brunswick, NJ, 2U.S. Geological Survey, Boulder, CO.

Geothermal waters are a significant source of arsenic, typically 1-10mgL-1; natural discharge to surface waters and aquifers usually results in increased arsenic levels affecting water quality in the boundary areas (Gihrin et al 2001). Arsenite [As(III)] is often the predominant valence of inorganic arsenic in geothermal waters and microbial activity has been associated with the rapid and efficient arsenic oxidation in such environments (Donahoe-Christieansen et al. 2004). In order to expand our knowledge on arsenic transformations enrichment cultures were established to study novel and diverse thermophiles and mesophiles associated with autotrophic arsenic oxidation from a geothermal spring in Yellowstone National Park and from hydrothermal sediments from the Guaymas Basin (Gulf of California). Sample inoculum (10% vol/vol) was added to mineral medium containing 5 mM arsenite [As(III)] and 10 mM carbonate, 15 ml aliquots were aerobically dispensed into 25 mL sterile serum bottles. The bottles were sealed with rubber stoppers and aluminum crimps to avoid evaporation and reaerated every five days at sampling time, to insure oxygenation, cultures were statically incubated at 37º and 60°C in the dark. Enrichments were established in triplicate with duplicate sterile controls. Stoichiometric arsenite oxidation in enrichment cultures in the active bottles was complete within 4 weeks of incubation under aerobic conditions in both mesophilic and thermophilic conditions for Yellowstone samples and thermophilic conditions for Guaymas samples. Arsenite was measured using high performance liquid chromatography (HPLC). In order to remove in-situ sediment three 50% dilutions of the active cultures were successfully made into new medium, incubated as previously described and pure cultures will be isolated.