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Hydrogen isotopic fractionation in lipid biosynthesis by H_2-consuming Desulfobacterium autotrophicum

Campbell, Brian J. and Li, Chao and Sessions, Alex L. and Valentine, David L. (2009) Hydrogen isotopic fractionation in lipid biosynthesis by H_2-consuming Desulfobacterium autotrophicum. Geochimica et Cosmochimica Acta, 73 (10). pp. 2744-2757. ISSN 0016-7037.

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We report hydrogen isotopic fractionations between water and fatty acids of the sulfate-reducing bacterium Desulfobacterium autotrophicum. Pure cultures were grown in waters with deuterium (D) contents that were systematically varied near the level of natural abundance (−37‰ ≤ δD ≤ 993‰). H_2 of constant hydrogen isotope (D/H) ratio was supplied to the cultures. The D/H ratios of water, H_2, and specific fatty acids were measured by isotope-ratio mass spectrometry. The results demonstrate that D. autotrophicum catalyzes hydrogen isotopic exchange between water and H_2, and this reaction is conclusively shown to approach isotopic equilibrium. In addition, variation in the D/H ratio of growth water accounts for all variation in the hydrogen isotopic composition of fatty acids. The D/H ratios of fatty acids from cultures grown on H_2/CO_2 are compared with those from a separate set of cultures grown on D-enriched formate, an alternative electron donor. This comparison rules out H_2 as a significant source of fatty acid hydrogen. Grown on either H_2/CO_2 or formate, D. autotrophicum produces fatty acids in which all hydrogen originates from water. For specific fatty acids, biosynthetic fractionation factors are mostly in the range 0.60 ≤ αFA–water ≤ 0.70; the 18:0 fatty acid exhibits a lower fractionation factor of 0.52. The data show that αFA_–water generally increases with length of the carbon chain from C_14 to C_17 among both saturated and unsaturated fatty acids. These results indicate a net fractionation associated with fatty acid biosynthesis in D. autotrophicum that is slightly smaller than in another H_2-consuming bacterium (Sporomusa sp.), but much greater than in most photoautotrophs.

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Sessions, Alex L.0000-0001-6120-2763
Additional Information:© 2009 Elsevier. Received 17 November 2008; accepted 19 February 2009. Available online 19 March 2009. Associate editor: Juske Horita. The authors gratefully acknowledge Robert Petty for D/H analyses of water, gas, and formate; Magnus Eek and Tsege Embaye for identification of fatty acids; Howard Berg and Joe Cisneros for assistance in fermentor maintenance; and Friedrich Widdel for advice on the cultivation of D. autotrophicum. Juske Horita and two anonymous reviewers provided useful commentary on the paper. This work was supported by the NASA Graduate Student Researcher Program (to B.J.C.) and Grants from the National Science Foundation (EAR-0311894 to D.L.V. and A.L.S. and EAR-0645502 to A.L.S.).
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NASA Graduate Student Research FellowshipUNSPECIFIED
Issue or Number:10
Record Number:CaltechAUTHORS:20090722-153238411
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Official Citation:Brian J. Campbell, Chao Li, Alex L. Sessions, David L. Valentine, Hydrogen isotopic fractionation in lipid biosynthesis by H2-consuming Desulfobacterium autotrophicum, Geochimica et Cosmochimica Acta, Volume 73, Issue 10, 15 May 2009, Pages 2744-2757, ISSN 0016-7037, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:14644
Deposited By: Jason Perez
Deposited On:08 Aug 2009 19:52
Last Modified:03 Oct 2019 00:51

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