Syntrophy via Interspecies H 2 Transfer between Christensenella and Methanobrevibacter Underlies Their Global Cooccurrence in the Human Gut

The human gut microbiome is made of trillions of microbial cells, most of which are Bacteria , with a subset of Archaea . The bacterial family Christensenellaceae and the archaeal family Methanobacteriaceae are widespread in human guts. They correlate with each other and with a lean body type. Whether species of these two families interact and how they affect the body type are unanswered questions. Here, we show that species within these families correlate with each other across people. We also demonstrate that particular species of these two families grow together in dense flocs, wherein the bacteria provide hydrogen gas to the archaea, which then make methane. When the archaea are present, the ratio of bacterial products (which are nutrients for humans) is changed. These observations indicate that when these species grow together, their products have the potential to affect the physiology of their human host.