Hydrogen Oxidation Benefits Alphaproteobacterial Methanotrophs Under Severe Methane Limitation

Abstract

Hydrogen (H 2 ) and methane (CH 4 ) are produced in the anoxic layers of wetlands and sediments. In the overlaying oxygenated surface layers, these gases become available for oxidation by aerobic hydrogenotrophic and methanotrophic microorganisms. While H 2 oxidation by verrucomicrobial methane‐oxidising bacteria (MOB) is extensively studied, less is known about this metabolism in MOB from the class Alphaproteobacteria , which frequently inhabit wetlands. We show that Methylocystis bryophila H2s T , Methylocapsa aurea KYG T , and “ Methylosinus acidophilus ” 29 encode diverse hydrogenases, instantly oxidise H 2 when cultivated under CH 4 ‐limited and low‐oxygen conditions, under which hydrogenase transcription is upregulated compared to CH 4 ‐replete conditions. H 2 exposure accelerated the maximum H 2 oxidation rates but caused no upregulation of hydrogenases. Furthermore, while CH 4 oxidation activity was affected by substrate‐limited growth conditions, H 2 oxidation rates remained unaffected, and H 2 supply to CH 4 ‐limited chemostats caused increased biomass yield. Moreover, CH 4 oxidation was severely inhibited by sulfide (H 2 S), while H 2 and methanol oxidation rates were only moderately affected. In summary, the ability to conserve energy from H 2 oxidation increases resilience and enhances growth of alphaproteobacterial methanotrophs in CH 4 ‐limited environments, which revises the ecological role of these MOB in ecosystems with naturally fluctuating CH 4 and H 2 concentrations.

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