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

Pseudomonas aeruginosa is a dangerous Gram-negative pathogen that causes severe infections. To survive and become more virulent, it needs iron, which it can obtain from the host. Previous research found that certain small regulatory RNAs called RsmY and RsmZ help the pathogen produce more of these beneficial traits when iron is scarce.

Now, scientists have discovered another sRNA called RsmW that is strongly increased when iron levels are low. This likely happens because of a protein called Fur. The researchers found that the RsmW molecule is cut from the end of a related RNA molecule called pa4570 mRNA, possibly by an enzyme known as RNAse E. Also, RsmW stays around longer than the longer pa4570-rsmW transcript and the modified pa4570 mRNA.

Interestingly, a protein named RetS that usually reduces RsmY and RsmZ levels actually boosts RsmW production when iron is limited. Furthermore, RsmW is important for the formation of biofilms, which are complex communities of bacteria that stick to surfaces and are difficult to eradicate. In an infection model using the deadly insect, Galleria mellonella, the researchers showed that RsmW is necessary for the pathogen to cause illness.

Lastly, they saw that RsmW is regulated in a similar way in chronic P. aeruginosa infections found in cystic fibrosis patients' sputum, suggesting that this iron-dependent regulation could play a key role in lung infections in CF patients. Overall, this study reveals a new way in which small RNA molecules can control how P. aeruginosa causes disease when iron is scarce.