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PeerJ. 2017 Oct 20;5:e3945. doi: 10.7717/peerj.3945. eCollection 2017.

Oxygen-limited metabolism in the methanotroph Methylomicrobium buryatense 5GB1C.

Author information

1
Department of Chemical Engineering, University of Washington, Seattle, WA, United States of America.
2
Allen Institute for Cell Science, Seattle, WA, USA.
3
InBios, Seattle, WA, USA.
4
Zymo Genetics, Seattle, WA, USA.
5
Department of Biology, George Washington University, Washington, D.C., USA.
6
eScience Institute, University of Washington, Seattle, WA, USA.
7
Department of Microbiology, University of Washington, Seattle, WA, USA.
#
Contributed equally

Abstract

The bacteria that grow on methane aerobically (methanotrophs) support populations of non-methanotrophs in the natural environment by excreting methane-derived carbon. One group of excreted compounds are short-chain organic acids, generated in highest abundance when cultures are grown under O2-starvation. We examined this O2-starvation condition in the methanotroph Methylomicrobium buryatense 5GB1. The M. buryatense 5GB1 genome contains homologs for all enzymes necessary for a fermentative metabolism, and we hypothesize that a metabolic switch to fermentation can be induced by low-O2 conditions. Under prolonged O2-starvation in a closed vial, this methanotroph increases the amount of acetate excreted about 10-fold, but the formate, lactate, and succinate excreted do not respond to this culture condition. In bioreactor cultures, the amount of each excreted product is similar across a range of growth rates and limiting substrates, including O2-limitation. A set of mutants were generated in genes predicted to be involved in generating or regulating excretion of these compounds and tested for growth defects, and changes in excretion products. The phenotypes and associated metabolic flux modeling suggested that in M. buryatense 5GB1, formate and acetate are excreted in response to redox imbalance. Our results indicate that even under O2-starvation conditions, M. buryatense 5GB1 maintains a metabolic state representing a combination of fermentation and respiration metabolism.

KEYWORDS:

Acetate; Excretion products; Methane; Methanotroph

Conflict of interest statement

Melissa Hendershott is currently an employee of the Allen Institute for Cell Science, Frances Chu is currently an employee of InBios, and Amanda Lee Smith is currently an employee of Zymo Genetics.

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