Phylogeny of water channel proteins family. See figure 5 for notations and Materials and Methods for details on phylogenetic reconstruction. The two homologs from Rhodobacter and Rhodopseudomonas are separated by a well-supported branch. The homologs grouping with Rhodobacter do not have a paralog among the homologs grouping with Rhodopseudomonas and vice versa. This QuartOP remains a strong candidate for horizontal gene transfer.