| In the environment, multiple microbial taxa typically coexist as communities, competing for resources, and often physically associated within biofilms. In this study, five dual species co-cultivation models were developed to identify molecular mechanisms in Pseudomonas aeruginosa that underlie multispecies microbial associations.; In P. aeruginosa and Agrobacterium tumefaciens coculture, P. aeruginosa had a distinct growth rate advantage, increasing its relative abundance during planktonic and biofilm growth. It also demonstrated a slight quorum sensing-dependent increase in growth yield in liquid cocultures. In coculture biofilms, P. aeruginosa dominated the population, "blanketing" or burying immature A. tumefaciens microcolonies. Quorum sensing mediated functions also contributed to the dominance by decreasing A. tumefaciens biomass in coculture biofilms. Flagellar and type IV pili mutant strains of P. aeruginosa exhibited deficient blanketing and impaired competition in coculture biofilms, while in planktonic coculture these mutations had no effect on competition. In contrast, A. tumefaciens used motility to emigrate from coculture biofilms. In both planktonic and biofilm cocultures A. tumefaciens remained viable for extended periods of time, coexisting with its more numerous competitor.; When P. aeruginosa was co-cultivated with Bacillus subtilis, Staphylococcus aureus, Vibrio cholerae or Pantoea stewartii, it out-competed in all liquid cocultures. Quorum sensing regulated functions, especially those also modulated by MvfR, enhanced P. aeruginosa's competitiveness by killing other species. Killing was further shown as multifactorial and distinct in different cocultures. Cyanide, pyocyanin, rhamnolipid and 2-heptyl-4-hydroxyquinoline N-oxide were identified as important killing factors for different species. In some cases specific synergistic interactions were discovered between these toxins, revealing a resemblance with clinically prescribed antibiotic "cocktail" for treating human bacterial infections. Quorum sensing played a role for P. aeruginosa to interact with V. cholerae in biofilms by increasing P. aeruginosa yield. The P. stewartii and S. aureus pure biofilms were found resistant to the P. aeruginosa secreted toxins, which were effective in liquid cocultures by synergistic interactions, indicating biofilm might be a way for killing sensitive species to establish a niche in the environment. |
