Reducing intracellular c-di-GMP content increases quorum sensing-regulated virulence in Pseudomonas aeruginosa

Pseudomonas aeruginosa is a leading causative agent in nosocomial infections, which is attributed to its ability to form robust biofilms and engage a series of virulence mechanisms. Cyclic-di-GMP (c-di-GMP), a secondary messenger found in most bacterial species, is well known to regulate P. aeruginosa biofilm formation. High intracellular c-di-GMP content enhances biofilm formation, while a reduction of the c-di-GMP content in biofilm cells leads to biofilm dispersal. It remains unclear how biofilm dispersal through c-di-GMP reduction will ‘prepare’ the dispersed cells for their subsequent planktonic lifestyle. Here, we show that cells with high and low intracellular c-di-GMP contents have distinct transcriptome profiles. Interestingly, quorum-sensing (QS)-controlled virulence factors such as rhamnolipids and pyocyanin were found to be highly expressed in cells with low intracellular c-di-GMP content compared to cells with higher c-di-GMP content. This correlates well with their intracellular survival rates and cytotoxicity after in vitro exposure to murine macrophages. Our data suggests that biofilm dispersal through c-di-GMP manipulation might induce QS-regulated virulence during infections.