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Published August 4, 2009 | Supplemental Material + Published
Journal Article Open

Large D/H variations in bacterial lipids reflect central metabolic pathways

Abstract

Large hydrogen-isotopic (D/H) fractionations between lipids and growth water have been observed in most organisms studied to date. These fractionations are generally attributed to isotope effects in the biosynthesis of lipids, and are frequently assumed to be approximately constant for the purpose of reconstructing climatic variables. Here, we report D/H fractionations between lipids and water in 4 cultured members of the phylum Proteobacteria, and show that they can vary by up to 500‰ in a single organism. The variation cannot be attributed to lipid biosynthesis as there is no significant change in these pathways between cultures, nor can it be attributed to changing substrate D/H ratios. More importantly, lipid/water D/H fractionations vary systematically with metabolism: chemoautotrophic growth (approximately −200 to −400‰), photoautotrophic growth (−150 to −250‰), heterotrophic growth on sugars (0 to −150‰), and heterotrophic growth on TCA-cycle precursors and intermediates (−50 to +200‰) all yield different fractionations. We hypothesize that the D/H ratios of lipids are controlled largely by those of NADPH used for biosynthesis, rather than by isotope effects within the lipid biosynthetic pathway itself. Our results suggest that different central metabolic pathways yield NADPH—and indirectly lipids—with characteristic isotopic compositions. If so, lipid δD values could become an important biogeochemical tool for linking lipids to energy metabolism, and would yield information that is highly complementary to that provided by ^(13)C about pathways of carbon fixation.

Additional Information

© 2009 by the National Academy of Sciences. This Feature Article is part of a series identified by the Editorial Board as reporting findings of exceptional significance. Edited by John M. Hayes, Woods Hole Oceanographic Institution, Woods Hole, MA, and approved May 29, 2009 (received for review March 19, 2009). Published online before print July 17, 2009, doi: 10.1073/pnas.0903030106 We thank A. Schimmelmann for substrate D/H analyses, M. Eek, and L. Zhang for assistance with lipid D/H analyses and J. Leadbetter and D. Newman and their respective research groups for providing insightful discussion and assistance with microbial cultures. This work was supported by National Science Foundation Grant EAR-0645502 (to A.L.S.) and a predoctoral fellowship (to X.Z.). Author contributions: X.Z. and A.L.S. designed research; X.Z., A.L.G., and A.L.S. performed research; X.Z. analyzed data; and X.Z. and A.L.S. wrote the paper. The authors declare no conflict of interest. This article is a PNAS Direct Submission. See Commentary on page 12565. This article contains supporting information online at www.pnas.org/cgi/content/full/0903030106/DCSupplemental.

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Published - Zhang2009p5576P_Natl_Acad_Sci_Usa.pdf

Supplemental Material - 0903030106SI.pdf

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