Cyclic-di-GMP is required for corneal infection byPseudomonas aeruginosaand modulates host immunity

Biofilms are extremely tolerant toward antimicrobial treatment and host immune clearance due to their distinct physiology and protection by extracellular polymeric substances. Bis-(3´-5´)-cyclic dimeric guanosine monophosphate (c-di-GMP) is an essential messenger that regulates biofilm formation by a wide range of bacteria. However, there is a lack of physiological characterization of biofilms in vivo as well as the roles of c-di-GMP signaling in mediating host-biofilm interactions. Here, we employed dual RNA-Seq to characterize the host and pathogen transcriptomes during Pseudomonas aeruginosa infection using a mouse keratitis model. In vivo P. aeruginosa biofilms maintained a distinct physiology compared with in vitro P. aeruginosa biofilms, with enhanced virulence and iron uptake capacity. C-di-GMP synthesis was enhanced in P. aeruginosa cells in vivo, potentially due to down-regulation of the expression of several phosphodiesterases (e.g., DipA, NbdA). Increased intracellular c-di-GMP levels were required for long-term ocular colonization of P. aeruginosa and impaired host innate immunity.