Priority changes between biofilm exopolysaccharides synthesis and rhamnolipids production are mediated by a c-di-GMP-specific phosphodiesterase NbdA in Pseudomonas aeruginosa

The synthesis of biofilm exopolysaccharides and rhamnolipids (RLs) are two interrelated processes in Pseudomonas aeruginosa, but how bacteria coordinate these two processes remains unclear. We collected a P. aeruginosa KT1115 with rugose small colony variant (RSCV) phenotype from soil, and used it to study the dynamic regulation mechanism of biofilm polysaccharide and RLs synthesis. The results showed that the overproduction of biofilm exopolysaccharides at biofilm stage ultimately contributed the surge of RLs production at RLs stage. This phenomenon was further verified by comparing PAO1 with its engineered RSCV mutant, PAO1ΔwspF. Further genomic, transcriptomic analyses and gene deletion revealed that downregulation of c-di-GMP level was the key to switch biofilm exopolysaccharides accumulation to RLs surge, by transcriptionally upregulating a c-di-GMP phosphodiesterase NbdA. Overall, this study demonstrates the importance of c-di-GMP in coordinating biofilm exopolysaccharides and RLs synthesis, and provides an inspiration for enhancing RLs production through regulating c-di-GMP level.