Differential impact on motility and biofilm dispersal of closely related phosphodiesterases in Pseudomonas aeruginosa

In Pseudomonas aeruginosa, the transition between planktonic and biofilm lifestyles is modulated by the intracellular secondary messenger cyclic dimeric-GMP (c-di-GMP) in response to environmental conditions. Here, we used gene deletions to investigate how the environmental stimulus nitric oxide (NO) is linked to biofilm dispersal, focusing on biofilm dispersal phenotype from proteins containing putative c-di-GMP turnover and Per-Arnt-Sim (PAS) sensory domains. We document opposed physiological roles for the genes Delta rbdA and Delta pa2072 that encode proteins with identical domain structure: while Delta rbdA showed elevated c-di-GMP levels, restricted motility and promoted biofilm formation, c-di-GMP levels were decreased in Delta pa2072, and biofilm formation was inhibited, compared to wild type. A second pair of genes, Delta fimX and Delta dipA, were selected on the basis of predicted impaired c-di-GMP turnover function: Delta fimX showed increased, Delta dipA decreased NO induced biofilm dispersal, and the genes effected different types of motility, with reduced twitching for Delta fimX and reduced swimming for Delta dipA. For all four deletion mutants we find that NO-induced biomass reduction correlates with increased NO-driven swarming, underlining a significant role for this motility in biofilm dispersal. Hence P. aeruginosa is able to differentiate c-di-GMP output using structurally highly related proteins that can contain degenerate c-di-GMP turnover domains.