HR: 0800h
AN: B11A-1024    [Abstracts]
TI: Carbon Isotope Fractionation In Biotic Vs. Abiotic Anaerobic Conditions
AU: * Gebrehiwet, T A
EM: tsigabu.gebrehiwet@wmich.edu
AF: Western Michigan University, Department of Geosciences 1187 Rood Hall 1903 West Michigan Ave, Kalamazoo, MI 49008 United States
AB: Dissimilatory metal reducing bacteria (DMRB) are thought to play an important role in the biogeochemical cycling of Fe, and nutrient elements such as C and P, in the anaerobic subsurface. The consumption of organic carbon sources (including contaminants) by these bacteria can significantly fractionate substrate C isotopes, however the effects of solution composition, electron acceptor, or electron donor on C isotopic fractionation by DMRB is at present poorly quantified. We have conducted experiments to compare the effects of bicarbonate (δ13C = -3‰) and phosphate buffers on carbon isotope fractionation by Shewanella putrefaciens strain 200R. The effects of dissolved carbonate and phosphate on δ13C values of dissolved inorganic C evolved during microbial reduction of ferric citrate (δ 13Cinitial = -25‰) were examined using sodium lactate (δ13Cinitial = -25‰) as electron donor under strict anaerobic conditions at neutral pH and 30°C, under dark and (fluorescent) light conditions. Our results suggest that bicarbonate may enhance the rate of Fe(III) reduction by S. putrefaciens, in comparison with media containing phosphate buffer but no added bicarbonate. Compared with phosphate buffered experiments, the presence of dissolved bicarbonate also resulted in a greater degree of C isotopic fractionation (ε=2-3‰ and ε=5-7‰, respectively). The effect of light on microbial Fe(III) reduction was negligible, however sterile controls showed a minor but significant quantity of carbon dioxide production in liquid media, most likely from photochemical decomposition of citrate. The abiotic experiments also showed measurable carbon isotope fractionation between the carbon dioxide produced and the organic carbon substrate which will be discussed.
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0418 Bioremediation
DE: 0428 Carbon cycling (4806)
DE: 0454 Isotopic composition and chemistry (1041, 4870)
SC: Biogeosciences [B]
MN: Fall Meeting 2005