KINETICS AND ENERGETICS OF MICROBIAL SULFATE REDUCTION IN ACIDIC HOT SPRINGS AT YELLOWSTONE NATIONAL PARK

Sulfur commonly exists in oxidation states from -2 to +6, and dissimilatory metabolism of these varied species has been widely documented in nearly all environments on earth’s surface. Comparatively fewer studies exist for sulfate reduction metabolism in high temperature acidic environments, especially those evaluating these organisms in situ. Several lines of evidence suggest this metabolism is prevalent in such environments; literature reports of isolates and the presence of dissimilatory sulfate reduction (DSR) genes have grown in recent years. This study combines kinetic and energic analyses of in situ rate experiments from such locations across Yellowstone National Park. Goals of this work include determining the prevalence of this process in situ, determining kinetics of sulfate reduction coupled to organic substrates, and characterizing the energy dissipation by these microbial communities. Anaerobic experiments were conducted in the field to measure the abundance of sulfate and small organic acids in 24 to 48 hour microcosm incubations. Experiments included a natural abundance incubation, and treatments with additions of acetic and lactic acids (small organic acids, or their deprotonated form), and molybdate-killed controls. Measurements of chemical species abundances are being performed via ion chromatography. The quantification of all reaction constituents during the time course of these incubations permits the quantification of energy availability and dissipation. This project is in the preliminary results phase, but early indicators suggest that this metabolism is indeed prevalent and that these communities contribute substantially to the dissipation of energy in reduced anoxic thermoacidophilic habitats.