HR: 0800h
AN: B21D-0917    [Abstracts]
TI: Hydrogen-Isotopic Systematics of Lipid Biosynthesis in Hydrogen-Consuming Anaerobes and Aerobes
AU: * Campbell, B J
EM: bjcampbell@umail.ucsb.edu
AF: Dept. of Geological Sciences, University of California, Bldg. 526, Santa Barbara, CA 93106-9630 United States
AU: Fox, D
EM: fox@umail.ucsb.edu
AF: Dept. of Molecular, Cellular, and Developmental Biology, University of California, Santa Barbara, CA 93106 United States
AU: Valentine, D L
EM: valentine@geol.ucsb.edu
AF: Dept. of Geological Sciences, University of California, Bldg. 526, Santa Barbara, CA 93106-9630 United States
AU: Sessions, A L
EM: als@gps.caltech.edu
AF: Division of Geological and Planetary Sciences, California Institute of Technology, MC 170-25, 1200 E. California Blvd., Pasadena, CA 91125 United States
AB: In anoxic sediments, molecular hydrogen (H$_{2}$) is a key intermediate in the transfer of electrons between H$_{2}$-producing (e.g., fermentative) bacteria and H$_{2}$-consuming microbes, including sulfate-reducing bacteria (SRB). H$_{2}$ is a potential source of lipid-bound hydrogen for SRB, as are water and organic matter. Relative to these other potential sources, H$_{2}$ typically is markedly depleted in deuterium. If hydrogen from strongly D-depleted H$_{2}$ is incorporated into SRB lipids, the isotopic signal could be preserved over geologic time in biomarker compounds in the sediments. The accumulation of characteristically D-depleted SRB biomarkers may thus provide a quantitative measure of sulfate reduction (and hence of carbon remineralization by SRB) in the ancient environment. Ongoing experiments are designed to quantify the relative contributions of H$_{2}$, water, and organic matter to lipid-bound hydrogen in SRB, as well as to determine the associated hydrogen-isotopic fractionations. {\it Desulfobacterium autotrophicum}, a facultative autotroph, is grown in pure culture under various isotopically defined conditions. Water in the media and key metabolites are monitored for D/H. The produced biomass is harvested, and D/H ratios of individual lipid compounds are measured. Isotopic mass-balance calculations based on these data will allow us to determine 1) hydrogen-isotopic compositions of SRB lipids, 2) effects of growth conditions on D/H ratios, and 3) the biochemical sources for lipid-bound hydrogen. Similar experiments are underway to identify and quantify the controls on stable hydrogen-isotopic fractionation during lipid biosynthesis in syntrophic cocultures and in pure cultures of H$_{2}$-consuming, aerobic (i.e., knallgas) bacteria. Taken together, these experiments will provide a first test of our hypothesis that D/H ratios in lipids can be used to quantify carbon remineralization by SRB in modern, and potentially ancient, sediments.
DE: 4802 Anoxic environments
DE: 4803 Bacteria
DE: 1040 Isotopic composition/chemistry
DE: 1055 Organic geochemistry
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting