RsmW is an iron-responsive 3' UTR derived small regulatory RNA that contributes to biofilm formation and virulence of Pseudomonas aeruginosa.

UNLABELLED: Pseudomonas aeruginosa is an opportunistic Gram-negative pathogen that causes acute and chronic opportunistic infections. Progression to chronic infection requires upregulation of the Rsm small regulatory RNAs (sRNAs), which in turn induce the expression of virulence factors to promote chronic virulence phenotypes, including biofilm formation. Iron is a critical nutrient for survival and virulence of Pa , and host-mediated iron limitation leads to the induction of key virulence factors driving infection. Prior work showed that the RsmY and RsmZ sRNAs are modestly upregulated due to iron limitation in static growth conditions via PqsR. Here, we show that another Rsm sRNA, RsmW, is strongly induced by iron limitation, likely in a Fur-dependent manner. We identified an RNA processing event, which appears to be mediated by the RNAse E, resulting in cleavage of RsmW from the 3' UTR of pa4570 mRNA. We also report that RsmW is more stable than the full length pa4570-rsmW transcript as well as the processed pa4570 mRNA. Surprisingly, we found that RetS, which down-regulates RsmY and RsmZ expression, enhances expression of RsmW under iron limiting conditions. We further demonstrate that RsmW plays a key role in biofilm formation under iron limiting conditions and is required for full pathogenesis in a Galleria mellonella infection model. Lastly, we observed similar iron-dependent regulation of RsmW in chronic infection isolates from cystic fibrosis (CF) sputum, underlining the potential importance of this regulation in the CF lung. Taken together, the results outline a new paradigm for sRNA-dependent iron regulation of P. aeruginosa pathogenesis.

AUTHOR SUMMARY: P. aeruginosa requires iron for its survival and virulence. Upon infection the mammalian host limits iron, which P. aeruginosa overcomes via numerous regulatory responses that play a central role in pathogenesis. He we report that iron starvation induces expression of the RsmW small regulatory sRNA, which regulates key virulence phenotypes that promote the progression of chronic infections in the CF lung. We show that RsmW is processed from the 3' untranslated region (UTR) of the pa4570 transcript, which is also induced upon iron starvation. Our studies also revealed regulatory events that are distinct from the previously characterized Rsm sRNAs, suggesting RsmW functions under distinct environmental conditions. Furthermore, we found that RsmW contributes to biofilm formation in flow cells, promotes killing in Galleria mellonella larvae, and is induced by CF isolates upon iron starvation. Taken together, our work demonstrates that RsmW is a novel iron-dependent regulator of chronic virulence traits in P. aeruginosa .