Genomic insights into adaptations of TMA-utilizing methanogens to diverse habitats including the human gut

Methanomassiliicoccales are a lesser known component of the human gut microbiota. This archaeal order is composed of methane producers that use methylated amines, such as trimethylamine, in methane production. This group has only one cultured representative; how they adapted to inhabit the mammalian gut and how they interact with other microbes is largely unknown. Using bioinformatics methods applied to DNA from a wide range of samples, we profiled the relative abundances of these archaea in environmental and host-associated microbial communities. We observed two groups of Methanomassiliicoccales, one largely host-associated and one largely found in environmental samples, with some exceptions. When host-associated, these archaea have a distinct set of genes related to adhesion and possess genes related to bile resistance. We did not detect Methanomassiliicoccales in all human populations tested but when present, they are correlated with Bacteria known to produce trimethylamine. Since trimethylamine is linked to cardiovascular disease risk, these intriguing Archaea may also be involved.