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Hydrogen isotope fractionation during H_2/CO_2 acetogenesis: hydrogen utilization efficiency and the origin of lipid-bound hydrogen

Valentine, D. L. and Sessions, A. L. and Tyler, S. C. and Chidthaisong, A. (2004) Hydrogen isotope fractionation during H_2/CO_2 acetogenesis: hydrogen utilization efficiency and the origin of lipid-bound hydrogen. Geobiology, 2 (3). pp. 179-188. ISSN 1472-4677. doi:10.1111/j.1472-4677.2004.00030.x.

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Hydrogen metabolism was studied in the anaerobic bacterium, Sporomusa sp. strain DMG 58, by measuring natural abundance levels of deuterium in H_2, H_(2)O, and individual fatty acids during acetogenic growth on H_2/CO_2. Four cultures were grown, each in medium with a distinct hydrogen-isotopic composition (δD-H_(2)O). The δD value of H_2 was quantified in the residual gas exiting the growth chambers and found to decrease concurrently with net H_2 consumption, indicating rapid isotope exchange between H_2 and H_(2)O. An isotopic mass balance was used to constrain the efficiency with which H_2 was activated by the cell and the reducing equivalents catabolized, which we term the H_2 utilization efficiency. Results indicate that H_2 utilization efficiency in these cultures is less than 20% during the growth phase, and less than 2% after the growth phase. The gross rate of cellular H_2 activation was similar in the growth phase and afterward. Biomass harvested at the end of each experiment was used to analyse the D/H of individual membrane lipids. Values of δD were highly correlated between lipids and water (δD-lipids = 0.59 × δD-water – 381‰; R2 = 0.995), indicating the source of lipid hydrogen is in isotopic equilibrium with water. Results are consistent with two possibilities: (i) water is the sole source of hydrogen to lipids, and the fractionation during biosynthesis is significantly larger than previously observed (α = 0.59), or (ii) hydrogen from H_2 is incorporated into lipids, but only after reaching isotopic equilibrium with H_(2)O. Fatty acids were strongly depleted in deuterium relative to all other organisms studied thus far, and such large depletions may prove useful as biomarkers for studying H_2 cycling in anoxic environments as well as in the geological record.

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Sessions, A. L.0000-0001-6120-2763
Additional Information:© 2004 Blackwell Publishing Ltd. Received 27 April 2004; accepted 28 July 2004. We thanked Cameron Adams and Ana Solberger who assisted with laboratory sampling. The manuscript was improved based on suggestions made by three anonymous reviewers. Funding for this work was provided by NSF Life in Extreme Environments special competition (0085607), the USDA (NRI-CGP award #99-35101-7809; to ST), an NSF Major Research Instrumentation Award (9871077; to ST), a Joan Irvine Smith Postdoctoral Fellowship (to AC), an NSF Postdoctoral Fellowship in Microbial Biology (0074368; to DLV), and the NSF Biogeosciences Program (0311894; to ALS and DLV). Special thanks to Doug Bartlett for providing space and resources for several of these experiments.
Funding AgencyGrant Number
U.S. Department of Agriculture99-35101-7809
Joan Irvine Smith Postdoctoral FellowshipUNSPECIFIED
NSF Postdoctoral FellowshipDBI-0074368
Issue or Number:3
Record Number:CaltechAUTHORS:20131120-101920612
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Official Citation:VALENTINE, D. L., SESSIONS, A. L., TYLER, S. C. and CHIDTHAISONG, A. (2004), Hydrogen isotope fractionation during H2/CO2 acetogenesis: hydrogen utilization efficiency and the origin of lipid-bound hydrogen. Geobiology, 2: 179–188. doi: 10.1111/j.1472-4677.2004.00030.x
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ID Code:42587
Deposited On:21 Nov 2013 21:21
Last Modified:10 Nov 2021 16:25

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