The Population Structure of Pseudomonas aeruginosa Is Characterized by Genetic Isolation of exoU+ and exoS+ Lineages

Egon A. Ozer*, Ekpeno Nnah, Xavier DIdelot, Rachel J. Whitaker, Alan R. Hauser, Howard Ochman

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

30 Scopus citations


The diversification of microbial populations may be driven by many factors including adaptation to distinct ecological niches and barriers to recombination. We examined the population structure of the bacterial pathogen Pseudomonas aeruginosa by analyzing whole-genome sequences of 739 isolates from diverse sources. We confirmed that the population structure of P. aeruginosa consists of two major groups (referred to as Groups A and B) and at least two minor groups (Groups C1 and C2). Evidence for frequent intragroup but limited intergroup recombination in the core genome was observed, consistent with sexual isolation of the groups. Likewise, accessory genome analysis demonstrated more gene flow within Groups A and B than between these groups, and a few accessory genomic elements were nearly specific to one or the other group. In particular, the exoS gene was highly overrepresented in Group A compared with Group B isolates (99.4% vs. 1.1%) and the exoU gene was highly overrepresented in Group B compared with Group A isolates (95.2% vs. 1.8%). The exoS and exoU genes encode effector proteins secreted by the P. aeruginosa type III secretion system. Together these results suggest that the major P. aeruginosa groups defined in part by the exoS and exoU genes are divergent from each other, and that these groups are genetically isolated and may be ecologically distinct. Although both groups were globally distributed and caused human infections, certain groups predominated in some clinical contexts.

Original languageEnglish (US)
Pages (from-to)1780-1796
Number of pages17
JournalGenome biology and evolution
Issue number7
StatePublished - Jul 1 2019


  • accessory genome
  • exoS
  • exoU
  • microbial evolution
  • population structure
  • recombination
  • whole-genome phylogenetics

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Genetics


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