Evolutionary history of dimethylsulfoniopropionate (DMSP) demethylation enzyme DmdA in marine bacteria

Dimethylsulfoniopropionate (DMSP), an osmolyte produced by oceanic phytoplankton, is predominantly degraded by bacteria belonging to theRoseobacterlineage and other marineAlphaproteobacteriavia DMSP-dependent demethylase A protein (DmdA). To date, the evolutionary history of DmdA gene family is unclear. Some studies indicate a common ancestry between DmdA and GcvT gene families and a co-evolution betweenRoseobacterand the DMSP-producing-phytoplankton around 250 million years ago (Mya). In this work, we analyzed the evolution of DmdA under three possible evolutionary scenarios: 1) a recent common ancestor of DmdA and GcvT, 2) a coevolution betweenRoseobacterand the DMSP-producing-phytoplankton, and 3) pre-adapted enzymes to DMSP prior toRoseobacterorigin. Our analyses indicate that DmdA is a new gene family originated from GcvT genes by duplication and functional divergence driven by positive selection before a coevolution betweenRoseobacterand phytoplankton. Our data suggest thatRoseobacteracquireddmdAby horizontal gene transfer prior to exposition to an environment with higher DMSP. Here, we propose that the ancestor that carried the DMSP demethylation pathway genes evolved in the Archean, and was exposed to a higher concentration of DMSP in a sulfur rich atmosphere and anoxic ocean, compared to recentRoseobacterecoparalogs (copies performing the same function under different conditions), which should be adapted to lower concentrations of DMSP.