Simultaneous sulfide and methane oxidation by an extremophile

Aerobic methanotrophic bacteria oxidize methane in sulfide-rich environments, even though hydrogen sulfide (H2S) inhibits methane oxidation and aerobic respiration. Here, Schmitz et al. show that a single microorganism can oxidize methane and H2S simultaneously, and this is associated with upregulation of a sulfide-insensitive terminal oxidase. Hydrogen sulfide (H2S) and methane (CH4) are produced in anoxic environments through sulfate reduction and organic matter decomposition. Both gases diffuse upwards into oxic zones where aerobic methanotrophs mitigate CH4 emissions by oxidizing this potent greenhouse gas. Although methanotrophs in myriad environments encounter toxic H2S, it is virtually unknown how they are affected. Here, through extensive chemostat culturing we show that a single microorganism can oxidize CH4 and H2S simultaneously at equally high rates. By oxidizing H2S to elemental sulfur, the thermoacidophilic methanotroph Methylacidiphilum fumariolicum SolV alleviates the inhibitory effects of H2S on methanotrophy. Strain SolV adapts to increasing H2S by expressing a sulfide-insensitive ba(3)-type terminal oxidase and grows as chemolithoautotroph using H2S as sole energy source. Genomic surveys revealed putative sulfide-oxidizing enzymes in numerous methanotrophs, suggesting that H2S oxidation is much more widespread in methanotrophs than previously assumed, enabling them to connect carbon and sulfur cycles in novel ways.

Automated summary

Aerobic methanotrophic bacteria can survive in sulfide-rich environments, despite the inhibitory effects of hydrogen sulfide (H2S) on methane oxidation and aerobic respiration. This is due to the upregulation of a sulfide-insensitive terminal oxidase, allowing the microorganism to oxidize both methane and H2S simultaneously.