The c-di-GMP phosphodiesterase BifA regulates biofilm development in Pseudomonas putida.

We previously showed the isolation of biofilm-persistent Pseudomonas putida mutants that fail to undergo biofilm dispersal upon entry in stationary phase. Two such mutants were found to bear insertions in PP0914, encoding a GGDEF/EAL domain protein with high similarity to Pseudomonas aeruginosa BifA. Here we show the phenotypic characterization of a ΔbifA mutant in P. putida KT2442. This mutant displayed increased biofilm and pellicle formation, cell aggregation in liquid medium and decreased starvation-induced biofilm dispersal relative to the wild type. Unlike its P. aeruginosa counterpart, P. putida BifA did not affect swarming motility. The hyperadherent phenotype of the ΔbifA mutant correlates with a general increase in cyclic diguanylate (c-di-GMP) levels, Congo Red-binding exopolysaccharide production and transcription of the adhesin-encoding lapA gene. Integrity of the EAL motif and a modified GGDEF motif (altered to GGDQF) were crucial for BifA activity, and c-di-GMP depletion by overexpression of a heterologous c-di-GMP phosphodiesterase in the ΔbifA mutant restored wild-type biofilm dispersal and lapA expression. Our results indicate that BifA is a phosphodiesterase involved in the regulation of the c-di-GMP pool and required for the generation of the low c-di-GMP signal that triggers starvation-induced biofilm dispersal.