RpoS Mutation Leads to Prolonged Biofilm Mode of Growth and a Higher Fitness in Pseudomonas Aeruginosa Biofilms

Abstract BackgroundPseudomonas aeruginosa is a notorious opportunistic pathogen causing various biofilm-related infections. Biofilm formation is a unique microbial strategy that allows P. aeruginosa to survive adverse conditions such as antibiotic treatment and human immune responses. ResultsIn this study, we experimentally evolved P. aeruginosa PAO1 biofilms for cyclic treatment in the presence of high dose of imipenem, and enriched hyperbiofilm mutants within six cycles in two independent lineages. The competition assay showed the evolved hyperbiofilm mutants can outcompete the ancestral strain within biofilm by prolonging the biofilm mode of growth but not in planktonic cultures. Whole-genome sequencing analysis revealed the hyperbiofilm phenotype is caused by point mutations in rpoS gene in all independently evolved mutants and the same mutation was found in P. aeruginosa clinical isolates. We further showed that mutation in rpoS enhanced biofilm formation by prolonging the biofilm mode of growth and elevating the intracellular c-di-GMP level. Mutation in rpoS increased pyocyanin production and virulence in both P. aeruginosa laboratory strains and clinical isolates. ConclusionHere, our study revealed that antibiotic treatment of biofilm-related P. aeruginosa infections might induce a hyperbiofilm phenotype via rpoS mutation, which might partially explain antimicrobial treatment failure of many P. aeruginosa biofilm-related infections.