Horizontally acquired DAP pathway as a unit of self-regulation.

In this study, we report the acquisition of the diaminopimelic acid (DAP) pathway of lysine biosynthesis in choanoflagellate Monosiga brevicollis and investigate how this pathway is incorporated and regulated in the established metabolic network. Our data show that all major genes related to the DAP pathway in Monosiga were acquired from bacteria and algae. Although an endogenous lysC exists in Monosiga, the newly acquired lysC is fused to lysA and used specifically for lysine biosynthesis. In addition, these acquired genes encode two key rate-limiting enzymes, thus conferring Monosiga a self-regulated unit with ability to generate lysine. Our data suggest that a newly acquired metabolic capability can be added to the recipient organism without disturbing the previously established metabolic network. This finding also implies that the biochemical system of the recipient organism may determine the type and function of genes to be acquired.