3’,5’-cyclic pyrimidine nucleotides modulate growth and biofilm formation in Pseudomonas aeruginosa

Pseudomonas aeruginosa (P. aeruginosa) is a frequent cause of chronic and nosocomial infections. Key features of P. aeruginosa are its ability to form biofilms and its resistance to several antibacterial drug classes. A known regulator of biofilm formation is bis-(3′,5′)-cyclic guanosine monophosphate (c-di-GMP). Other cyclic nucleotides (cNMPs) as signal transducers, such as 3’,5’-cNMPs, are just moving into spotlight. Recently, 3’,5’-cyclic uridylyl monophosphate (cUMP) and -cytidylyl monophosphate (cCMP) came into focus as mediators of bacterial immunity against phages.

Here, we investigate the role of cCMP and -cUMP in bacterial growth, metabolism and susceptibility to antibacterial drugs.

Bacterial cultures were exposed to 3’,5’-cNMPs and their respective acetoxymethyl esters and growth kinetics, biofilm formation, and metabolomic changes were assessed.

Of the 3’,5-cNMPs, only cUMP could be detected in growing bacterial cultures. Facing limited nutrient supply, bacteria exposed to cCMP-AM growed slower and showed increased susceptibility against gentamicin and azithromycin, but not against carbenicillin. While not affecting growth kinetics, cUMP impacted biofilm formation and increased c-di-GMP as well as quorum sensing autoinducers.

Understanding the mechanism, by which cCMP exerts its “sensitizing” effect against antibacterial drugs and/or by which cUMP interacts with the c-di-GMP and QS pathways in regulating biofilm formation may lead to new strategies in overcoming certain bacterial resistances. Furthermore, the generator of endogenous cUMP found in growing bacterial cultures remains elusive, since currently, cCMP and cUMP have been reported to be produced only after phage infections or in host cells infected with bacterial effector proteins.