Simultaneous sulfide and methane oxidation by an extremophile.

Hydrogen sulfide (H 2 S) and methane (CH 4 ) are produced in anoxic environments through sulfate reduction and organic matter decomposition. Both gases diffuse upwards into oxic zones where aerobic methanotrophs mitigate CH 4 emissions by oxidizing this potent greenhouse gas. Although methanotrophs in myriad environments encounter toxic H 2 S, it is virtually unknown how they are affected. Here, through extensive chemostat culturing we show that a single microorganism can oxidize CH 4 and H 2 S simultaneously at equally high rates. By oxidizing H 2 S to elemental sulfur, the thermoacidophilic methanotroph Methylacidiphilum fumariolicum SolV alleviates the inhibitory effects of H 2 S on methanotrophy. Strain SolV adapts to increasing H 2 S by expressing a sulfide-insensitive ba 3 -type terminal oxidase and grows as chemolithoautotroph using H 2 S as sole energy source. Genomic surveys revealed putative sulfide-oxidizing enzymes in numerous methanotrophs, suggesting that H 2 S oxidation is much more widespread in methanotrophs than previously assumed, enabling them to connect carbon and sulfur cycles in novel ways.