The Pseudomonas aeruginosa PrrF sRNAs promote biofilm formation at body temperature

Pseudomonas aeruginosa is a Gram-negative opportunistic pathogen that causes both acute and chronic infections in vulnerable populations. Treatment of P. aeruginosa infections is increasingly challenging due to multi-drug resistance as well as biofilm formation that further increases antibiotic tolerance. Iron, which is sequestered by the host innate immune system, is also a key nutrient that required for P. aeruginosa biofilm formation. Previous work showed that the iron-responsive PrrF small regulatory RNAs (sRNAs), which are key to P. aeruginosas iron starvation response and required for virulence in murine lung infection, are dispensable for biofilm formation. However, these studies were performed using flow-cell biofilms at room temperature. Here we demonstrate a temperature dependency for PrrF in P. aeruginosa biofilm formation - the genes for these sRNAs are required for optimal biofilm formation at 37{degrees}C but not 25{degrees}C. We further show that the {Delta}prrF mutant lacks a yet-to-be identified surface appendage that is produced at 37{degrees}C but not 25{degrees}C. These studies demonstrate that the importance of the PrrF sRNAs in P. aeruginosa biofilm formation at body temperature and reveal a previously under-appreciated role of temperature in iron homeostasis and P. aeruginosa biofilm physiology. IMPORTANCEBiofilm formation is a critical aspect of pathogenesis for many microbial pathogens as it confers increased tolerance to the host immune system and antimicrobial treatments. Pseudomonas aeruginosa is an opportunistic pathogen that forms biofilms during infection, resulting in antimicrobial tolerance and treatment failure. Iron is a known requirement for P. aeruginosa biofilm formation, yet the precise role of iron homeostasis in biofilm physiology remains unclear. Here we show that temperature alters the requirement for the PrrF small regulatory RNAs, key components of P. aeruginosas iron starvation response, for biofilm formation. Specifically, PrrF is required for the optimal formation of biofilms in flow cells at 37{degrees}C but not 25{degrees}C, yet most flow-cell biofilm studies are conducted at 25{degrees}C. These results demonstrate a previously under-appreciated role of temperature in P. aeruginosa biofilm physiology.