Horizontal gene transfer in the molecular evolution of mannose PTS transporters.

The phosphoenolpyruvate:carbohydrate phosphotransferase system (PTS) represents hitherto the only example of group translocation transport systems. PTS transporters are exclusively found in bacteria and can be grouped on the basis of sequence and structure into six classes. We have analyzed the evolution of mannose-class PTS transporters. These transporters have a limited distribution among bacteria being mostly harbored by species associated to animals. The results obtained indicate that these genes have undergone a complex evolutionary history, including extensive horizontal gene transfer events, duplications, and nonorthologous displacements. The phylogenetic analysis revealed an early diversification to specialize in different transport capabilities, but these events have also occurred relatively recently. In addition, these transporters can be further divided into seven groups and this division correlates with their transport capabilities. Finally, the consideration of the genomic context allowed us to propose putative functional roles for some uncharacterized PTS transporters. The functional role and distribution of mannose-class PTS transporters suggest that their expansion may have played a significant role in the establishment of symbiotic relationships between animals and some bacteria.