Virulent strains of Pseudomonas aeruginosa are more disruptive during invasion of a microbial model community

Pseudomonas aeruginosa, a major opportunistic pathogen involved in cystic fibrosis and many nosocomial infections, exhibits strong competitive abilities in microbial communities. However, the mechanisms underlying its competitive success remain poorly understood. To investigate this, we introduced two P. aeruginosa strains-the moderately virulent PAO1 and the highly virulent PA14-into the THOR (The Hitchhikers Of the Rhizosphere) microbial model community, consisting of Pseudomonas koreensis, Flavobacterium johnsoniae, and Bacillus cereus. Our results show that P. aeruginosa invasion significantly disrupts THOR biofilms, with greater reductions in biofilm biomass and shifts in microbial composition observed with PA14 compared to PAO1. This suggests that virulence traits expressed by P. aeruginosa play critical roles also in its ability to outcompete resident microbes. Additionally, we examined the competitive impact of an O-antigen-deficient P. aeruginosa strain, showing further reduced competitive ability with other community members. While our model system has limitations in replicating host-associated environments, it provides valuable insights into P. aeruginosa's ecological strategies, with implications for understanding its competitive behaviour in community settings.