Tracking the Origins of Pseudomonas Aeruginosa Phylogroups by Diversity and Evolutionary Analysis of Important Pathogenic Marker Genes

Pseudomonas aeruginosa is a widespread environmental bacterium and an opportunistic pathogen that represents a health hazard due to its production of virulence factors and its high antibiotic resistance. The genome of most of the strains belonging to this bacterial species is highly conserved, and genes coding for virulence-associated traits are part of the species core-genome. Recently, the existence of phylogroups has been documented based on the analysis of whole genome sequences of hundreds of isolates. These clades contain both clinical and environmental strains, which show no particular geographical distribution. The major phylogroups (clades 1 and 2) are characterized by the nearly mutually exclusive production of the virulence effectors secreted by the type three secretion system (T3SS) ExoS and ExoU, respectively. Clade 3 is the most genetically diverse and shares with clade 5, which is closely related to clades 1 and 2, the production of the pore-forming exolysin A, and the lack of T3SS, among other characteristics. Here we analyze the 4955 P. aeruginosa genomes deposited in the Pseudomonas Genome Database and present some hypotheses on the origins of four of the five phylogroups of this bacterial species.