Bacterial and Eukaryotic Phosphoketolases: Phylogeny, Distribution and Evolution

Phosphoketolases (XFPs) are glycolytic enzymes present in several organisms belonging to the <i>Eukarya</i> and <i>Bacteria</i> domains. A total of 151 putative <i>xfp</i> genes were detected in 650 complete genomes available in public databases. Elimination of redundant sequences and pseudogenes rendered a final data set of 128 phosphoketolases, which was analyzed by phylogenetic methods. The distribution of <i>xfp</i> genes was uneven in most taxonomic groups, with the exception of the taxonomical division Lactobacillaceae, in which all the species studied harbored a putative <i>xfp</i> gene. Putative <i>xfp</i> genes were also present predominantly in <i>Rhizobiales</i> and <i>Actinobacteria</i> divisions, in which 23 out of 28 genomes and 23 out of 41 genomes contained at least one putative <i>xfp</i> homolog, respectively. Phylogenetic analyses showed clear discordance with the expected order of organismal descent even in groups where <i>xfp</i> is prevalent, such as <i>Lactobacillaceae.</i> The presence of putative paralogs in some organisms cannot account for these discrepancies; instead, these paralogs are most possibly xenologs. The results of the phylogenetic analyses, the distribution of <i>xfp</i> genes and the location of some <i>xfp</i> genes in plasmids are independent pieces of evidence that point to horizontal gene transfer as a major driving force in the evolution of phosphoketolases.