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Hydrogen isotope fractionation in lipids of the methane-oxidizing bacterium Methylococcus capsulatus

Sessions, Alex L. and Jahnke, Linda L. and Schimmelmann, Arndt and Hayes, John M. (2002) Hydrogen isotope fractionation in lipids of the methane-oxidizing bacterium Methylococcus capsulatus. Geochimica et Cosmochimica Acta, 66 (22). pp. 3955-3969. ISSN 0016-7037. doi:10.1016/S0016-7037(02)00981-X.

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Hydrogen isotopic compositions of individual lipids from Methylococcus capsulatus, an aerobic, methane-oxidizing bacterium, were analyzed by hydrogen isotope-ratio-monitoring gas chromatography–mass spectrometry (GC-MS). The purposes of the study were to measure isotopic fractionation factors between methane, water, and lipids and to examine the biochemical processes that determine the hydrogen isotopic composition of lipids. M. capsulatus was grown in six replicate cultures in which the δD values of methane and water were varied independently. Measurement of concomitant changes in δD values of lipids allowed estimation of the proportion of hydrogen derived from each source and the isotopic fractionation associated with the utilization of each source. All lipids examined, including fatty acids, sterols, and hopanols, derived 31.4 ± 1.7% of their hydrogen from methane. This was apparently true whether the cultures were harvested during exponential or stationary phase. Examination of the relevant biochemical pathways indicates that no hydrogen is transferred directly (with C-H bonds intact) from methane to lipids. Accordingly, we hypothesize that all methane H is oxidized to H_2O, which then serves as the H source for all biosynthesis, and that a balance between diffusion of oxygen and water across cell membranes controls the concentration of methane-derived H_2O at 31%. Values for α_(l/w), the isotopic fractionation between lipids and water, were 0.95 for fatty acids and 0.85 for isoprenoid lipids. These fractionations are significantly smaller than those measured in higher plants and algae. Values for α_(l/m), the isotopic fractionation between lipids and methane, were 0.94 for fatty acids and 0.79 for isoprenoid lipids. Based on these results, we predict that methanotrophs living in seawater and consuming methane with typical δD values will produce fatty acids with δD between −50 and −170‰, and sterols and hopanols with δD between −150 and −270‰.

Item Type:Article
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Sessions, Alex L.0000-0001-6120-2763
Schimmelmann, Arndt0000-0003-4648-5253
Additional Information:© 2002 Elsevier Science Ltd. Received December 10, 2001; accepted in revised form June 7, 2002. The authors gratefully acknowledge the assistance of Tsege Embaye, Sean Sylva, Kendra Turk, and Nacinda Lerner in preparing and analyzing M. capsulatus cultures. Dan Rothman provided assistance and advice on techniques of multivariate regression. Roger Summons, David DesMarais, and Kathleen Londry all contributed to productive discussions about this research. Nils Andersen and two anonymous reviewers provided many helpful suggestions and comments. A.L.S. and J.M.H. are supported by NSF OCE-9986727 and NASA NAG5-9422. A.S. is supported by DOE grant DE-FG02-00ER15032. Collaboration between WHOI and NASA Ames was facilitated by the NASA Astrobiology Institute.
Funding AgencyGrant Number
Department of Energy (DOE)DE-FG02-00ER15032
Issue or Number:22
Record Number:CaltechAUTHORS:20130626-112758754
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Official Citation:Alex L Sessions, Linda L Jahnke, Arndt Schimmelmann, John M Hayes, Hydrogen isotope fractionation in lipids of the methane-oxidizing bacterium Methylococcus capsulatus, Geochimica et Cosmochimica Acta, Volume 66, Issue 22, 15 November 2002, Pages 3955-3969, ISSN 0016-7037,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:39106
Deposited By: Tony Diaz
Deposited On:02 Jul 2013 18:33
Last Modified:09 Nov 2021 23:42

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