Archaea and the human gut: New beginning of an old story

Figure 3 Faith of trimethylamine originating from the gut microbiota metabolism and putative role of representatives of Methanomassiliicoccales. A: Several common foods (containing lecithin/choline, L-carnitine, trimethylamine oxide,…) are metabolized into trimethylamine (TMA) by some bacterial components of the microbiota; B: When the microbiota does not contain any members of the 7^th order of methanogens, the gut-originating TMA reaches the liver, where it is oxidized by the flavin-monoxygenase FMO3 into trimethylamine oxide (TMAO) (Blue arrows in B). This odorless molecule has recently been shown to be associated to cardiovascular diseases (CVD) and has pro-atherogenic properties. In some people however, with a deficiency in liver oxidation, the TMA is not or less metabolized (orange arrows in B) and reaches various body fluids, leading to trimethylaminuria (TMAU) or “fish-odor syndrome”; C: When present, either naturally or by supplementation (Archaebiotics), it is hypothesized that members of the 7^th order of methanogens, through their up to now unique metabolism in the gut, might decrease the concentration of TMA by converting it into methane, therefore leading to an archaea-mediated TMA depletion before it can reach the liver. This could therefore be a convenient way to prevent CVD or limit TMAU.