Aerobic methane production by methylotrophic Methylotenera in groundwater

Methylotenera are signature denitrifiers and methylotrophs commonly found together with methanotrophic bacteria in lakes and freshwater sediments. Here we show that three distinct Methylotenera ecotypes were abundant in methane-rich, Pleistocene-aged groundwaters. Just like in surface water biomes, groundwater Methylotenera often co-occurred with methane-oxidizing bacteria, even though they were generally unable to denitrify. One abundant Methylotenera ecotype expressed a pathway for aerobic methane production from methylphosphonate. This phosphate-acquisition strategy was recently found to contribute to methane production in the oligotrophic, oxic upper ocean. Gene organization, phylogeny and 3D protein structure of the key enzyme, C-P lyase subunit PhnJ were consistent with a role in phosphate uptake. We conclude that phosphate may be a limiting nutrient in productive, methane rich aquifers and that methylphosphonate degradation can contribute to groundwater methane production.