A rhlI 5' UTR-derived sRNA regulates RhlR-dependent quorum sensing in Pseudomonas aeruginosa

Acyl-homoserine lactone (AHL) quorum sensing (QS) controls expression of over 200 genes in Pseudomonas aeruginosa. There are two AHL regulatory systems, the LasR-LasI circuit, and the RhlR-RhlI system. We mapped transcription termination sites affected by AHL QS in P. aeruginosa and in doing so we identified AHL-regulated sRNAs. We focused on one particular sRNA in the rhlI locus. We found that rhlI, which encodes the enzyme that produces the AHL N-butanoyl-homoserine lactone (C4-HSL), is controlled by a 5' UTR derived sRNA we name RhlS. We also identified an antisense RNA encoded opposite the rhlI start codon, which we name asRhlS. RhlS accumulates as wild-type cells enter stationary phase and it is required for production of normal levels of C4-HSL through activation of rhlI translation. RhlS also directly represses translation of at least one other unlinked gene, fpvA. The asRhlS is at maximal levels during logarithmic growth, and we suggest the asRhlS may be antagonistic to RhlS. The rhlI-encoded sRNAs represent a novel aspect of RNA-mediated tuning of P. aeruginosa QS.