PNAS Plus: Carbon and sulfur back flux during anaerobic microbial oxidation of methane and coupled sulfate reduction

Holler, T., Wegener, G., Niemann, H., Deusner, Christian, Ferdelman, T. G., Boetius, A., Brunner, B. and Widdel, F. (2011) PNAS Plus: Carbon and sulfur back flux during anaerobic microbial oxidation of methane and coupled sulfate reduction Proceedings of the National Academy of Sciences of the United States of America, 108 (52). E1484-E1490. DOI 10.1073/pnas.1106032108.

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Microbial degradation of substrates to terminal products is commonly understood as a unidirectional process. In individual enzymatic reactions, however, reversibility (reverse reaction and product back flux) is common. Hence, it is possible that entire pathways of microbial degradation are associated with back flux from the accumulating product pool through intracellular intermediates into the substrate pool. We investigated carbon and sulfur back flux during the anaerobic oxidation of methane (AOM) with sulfate, one of the least exergonic microbial catabolic processes known. The involved enzymes must operate not far from the thermodynamic equilibrium. Such an energetic situation is likely to favor product back flux. Indeed, cultures of highly enriched archaeal–bacterial consortia, performing net AOM with unlabeled methane and sulfate, converted label from 14C-bicarbonate and 35S-sulfide to 14C-methane and 35S-sulfate, respectively. Back fluxes reached 5% and 13%, respectively, of the net AOM rate. The existence of catabolic back fluxes in the reverse direction of net reactions has implications for biogeochemical isotope studies. In environments where biochemical processes are close to thermodynamic equilibrium, measured fluxes of labeled substrates to products are not equal to microbial net rates. Detection of a reaction in situ by labeling may not even indicate a net reaction occurring in the direction of label conversion but may reflect the reverse component of a so far unrecognized net reaction. Furthermore, the natural isotopic composition of the substrate and product pool will be determined by both the forward and back flux. This finding may have to be considered in the interpretation of stable isotope records.

Document Type: Article
Additional Information: This article contains supporting information online at
Keywords: element cycle ; anaerobic methanotrophy ; biological thermodynamics ; Haldane relationship
Research affiliation: OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-MG Marine Geosystems
Refereed: Yes
DOI etc.: 10.1073/pnas.1106032108
ISSN: 0027-8424
Date Deposited: 05 Dec 2012 11:26
Last Modified: 25 Oct 2016 07:13

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