HR: 0800h
AN: B21B-0892    [Abstracts]
TI: Organic Acids as Hetrotrophic Energy Sources in Hydrothermal Systems
AU: Windman, T O
EM: todd.windman@asu.edu
AF: Arizona State University, Department of Chemistry and Biochemistry, Tempe, Az 85287-1604
AU: Zolotova, N
EM: nzolotova@asu.edu
AF: Arizona State University, Department of Chemistry and Biochemistry, Tempe, Az 85287-1604
AU: * Shock, E
EM: eshock@asu.edu
AF: Arizona State University, Department of Chemistry and Biochemistry, Tempe, Az 85287-1604
AB: Many thermophilic microbes are heterotrophs, but little is known about the organic compounds present in hydrothermal ecosystems. More is known about what these organisms will metabolize in lab experiments than what they do metabolize in nature. In an effort to bridge this gap, we have begun to incorporate organic analyses into ongoing research on Yellowstone hydrothermal ecosystems. After filtering at least a liter of hot spring water to minimize contamination, samples were collected into sixty-milliliter serum vials containing ultra-pure phosphoric acid, sodium hydroxide, or benzalkonium chloride. Approximately 80 sites were sampled spanning temperatures from 60 to $90\degC$ and pH values from 2 to 9. Analytical data for organic acid anions (including formate, acetate, lactate, and succinate) were obtained by ion chromatography. Preliminary results indicate that concentrations of organic acids anions range from 5 to 300 ppb. These results can be used with other field and lab data (sulfate, sulfide, nitrate, ammonia, bicarbonate, pH, hydrogen) in thermodynamic calculations to evaluate the amounts of energy available in heterotrophic reactions. Preliminary results of such calculations show that sulfate reduction to sulfide coupled to succinate oxidation to bicarbonate yields about 6 kcal per mole of electrons transferred. When formate oxidation to bicarbonate or hydrogen oxidation to water is coupled to sulfate reduction there is less energy available by approximately a factor of two. A comparison with nitrate reduction to ammonia involving succinate and/or formate oxidation reveals several similarities. Using formate to reduce nitrate can yield about as much energy as nitrate reduction with hydrogen (typically 12 to 14 kcal per mole of electrons transferred), but using succinate can yield more than twice as much energy. In fact, reduction of nitrate with succinate can provide more energy than any of the inorganic nitrate reduction reactions involving sulfur, iron minerals, sulfide, carbon monoxide or methane in Yellowstone hot springs. This difference suggests that small organic compounds in hydrothermal fluids can be major sources of metabolic energy for microbes, and may explain why so many heterotrophs are found in themophilic microbial culture experiments.
DE: 8424 Hydrothermal systems (8135)
DE: 1055 Organic geochemistry
DE: 0400 Biogeosciences
DE: 1000 GEOCHEMISTRY (New field, replaces Rock Chemistry)
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting