Hydrogen isotopic fractionation in lipid biosynthesis by H-2-consuming Desulfobacterium autotrophicum Journal Article uri icon

DCO ID 11121/7686-7262-9352-2001-CC

in language

  • eng

year of publication

  • 2009


  • 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 parts per thousand <= delta D <= 993 parts per thousand). H-2 of constant hydrogen isotope (D/H) ratio was supplied to the cultures. The D/H ratios of water, H,, 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/CO2 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/CO2 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 <= alpha(FA) water <= 0.70; the 18:0 fatty acid exhibits a lower fractionation factor of 0.52. The data show that alpha(FA-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 mother H-2-consuming bacterium (Sporomusa sp.), but much greater than in most photoautotrophs. (C) 2009 Elsevier Ltd. All rights reserved.


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