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²H/¹H variation in microbial lipids is controlled by NADPH metabolism

Wijker, Reto S. and Sessions, Alex L. and Fuhrer, Tobias and Phan, Michelle (2019) ²H/¹H variation in microbial lipids is controlled by NADPH metabolism. Proceedings of the National Academy of Sciences of the United States of America, 116 (25). pp. 12173-12182. ISSN 0027-8424. PMCID PMC6589753. doi:10.1073/pnas.1818372116.

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The hydrogen-isotopic compositions (²H/¹H ratios) of lipids in microbial heterotrophs are known to vary enormously, by at least 40% (400‰) relative. This is particularly surprising, given that most C-bound H in their lipids appear to derive from the growth medium water, rather than from organic substrates, implying that the isotopic fractionation between lipids and water is itself highly variable. Changes in the lipid/water fractionation are also strongly correlated with the type of energy metabolism operating in the host. Because lipids are well preserved in the geologic record, there is thus significant potential for using lipid ^2H/^1H ratios to decipher the metabolism of uncultured microorganisms in both modern and ancient ecosystems. But despite over a decade of research, the precise mechanisms underlying this isotopic variability remain unclear. Differences in the kinetic isotope effects (KIEs) accompanying NADP+ reduction by dehydrogenases and transhydrogenases have been hypothesized as a plausible mechanism. However, this relationship has been difficult to prove because multiple oxidoreductases affect the NADPH pool simultaneously. Here, we cultured five diverse aerobic heterotrophs, plus five Escherichia coli mutants, and used metabolic flux analysis to show that ²H/¹H fractionations are highly correlated with fluxes through NADP+-reducing and NADPH-balancing reactions. Mass-balance calculations indicate that the full range of ²H/¹H variability in the investigated organisms can be quantitatively explained by varying fluxes, i.e., with constant KIEs for each involved oxidoreductase across all species. This proves that lipid ²H/¹H ratios of heterotrophic microbes are quantitatively related to central metabolism and provides a foundation for interpreting ²H/¹H ratios of environmental lipids and sedimentary hydrocarbons.

Item Type:Article
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URLURL TypeDescription Information CentralArticle
Wijker, Reto S.0000-0001-5104-9849
Sessions, Alex L.0000-0001-6120-2763
Alternate Title:2H/1H variation in microbial lipids is controlled by NADPH metabolism
Additional Information:© 2019 National Academy of Sciences. Published under the PNAS license. Edited by James R. Ehleringer, University of Utah, Salt Lake City, UT, and approved April 29, 2019 (received for review October 25, 2018). We thank Jared Leadbetter for use of laboratory facilities and for providing helpful discussion and assistance with microbial cultures; Fenfang Wu and Stephanie Connon for laboratory assistance; and Megan Bergkessel for assistance with the plate reader and for providing P. fluorescens strains. This work was supported by National Science Foundation Award EAR-1529120 (to A.L.S.); and Swiss National Science Foundation Early Postdoc Mobility Fellowship P2EZP2 159080 (to R.S.W.). Author contributions: R.S.W. and A.L.S. designed research; R.S.W., T.F., and M.P. performed research; R.S.W., A.L.S., and T.F. analyzed data; and R.S.W., A.L.S., and T.F. wrote the paper. The authors declare no conflict of interest. This article is a PNAS Direct Submission. This article contains supporting information online at
Funding AgencyGrant Number
Swiss National Science Foundation (SNSF)P2EZP2 159080
Subject Keywords:hydrogen isotopes; fatty acids; fractionation; metabolic flux analysis; NADPH
Issue or Number:25
PubMed Central ID:PMC6589753
Record Number:CaltechAUTHORS:20190531-155520679
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Official Citation:2H/1H variation in microbial lipids is controlled by NADPH metabolism. Reto S. Wijker, Alex L. Sessions, Tobias Fuhrer, Michelle Phan. Proceedings of the National Academy of Sciences Jun 2019, 116 (25) 12173-12182; DOI: 10.1073/pnas.1818372116
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:96022
Deposited By: Tony Diaz
Deposited On:31 May 2019 23:09
Last Modified:16 Feb 2022 23:34

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