The phosphodiesterase DipA (PA5017) is essential for Pseudomonas aeruginosa biofilm dispersion

Although little is known regarding the mechanism of biofilm dispersion, it is becoming clear that this process coincides with alteration of cyclic di-GMP (c-di-GMP) levels. Here, we demonstrate that dispersion by Pseudomonas aeruginosa in response to sudden changes in nutrient concentrations resulted in increased phosphodiesterase activity and reduction of c-di-GMP levels compared to biofilm and planktonic cells. By screening mutants inactivated in genes encoding EAL domains for nutrient-in-duced dispersion, we identified in addition to the previously reportedrbdAmutant a secondmutant, thedipA strain (PA5017 [dispersion-induced phosphodiesterase A]), to be dispersion deficient in response to glutamate, nitric oxide, ammonium chlo-ride, and mercury chloride. Using biochemical and in vivo studies, we show that DipA associates with the membrane and exhib-its phosphodiesterase activity but no detectable diguanylate cyclase activity. Consistent with these data, adipAmutant exhib-ited reduced swarmingmotility, increased initial attachment, and polysaccharide production but only somewhat increased biofilm formation and c-di-GMP levels. DipA harbors an N-terminal GAF (cGMP-specific phosphodiesterases, adenylyl cyclases, and FhlA) domain and two EALmotifs within or near the C-terminal EAL domain. Mutational analyses of the two EALmotifs of DipA suggest that both are important for the observed phosphodiesterase activity and dispersion, while the GAF domainmodu-lated DipA function both in vivo and in vitro without being required for phosphodiesterase activity. Dispersion was found to require protein synthesis and resulted in increased dipA expression and reduction of c-di-GMP levels. We propose a role of DipA in enabling dispersion in P. aeruginosa biofilms