MULTIPLE HOMOLOGS OF LUXR AND LUXL CONTROL EXPRESSION OF VIRULENCE DETERMINANTS AND SECONDARY METABOLITES THROUGH QUORUM SENSING IN PSEUDOMONAS-AERUGINOSA PAO1

In Pseudomonas aeruginosa PAO1, expression of elastase is dependent up on an interaction between the positive transcriptional activator LasR and the autoinducer molecule N-(3-oxododecanoyl)-L-homoserine lactone (OdDHL), the synthesis of which is directed by Lasl. Previously we hav e shown that in PAN057, an elastase-negative mutant of PAO1, elastase production can be restored to some extent by addition of exogenous N-( 3-oxohexanoyl)-L-homoserine lactone (OHHL), Here we report that PAN067 is also defective in the production of alkaline protease, haemolysin, cyanide, pyocyanin and autoinducer(s). As neither addition of exogeno us OdDHL nor introduction of lasR restored PAN067 to the parental phen otype, we sought to complement PAN067 with PAO1 DNA. From a cosmid lib rary, a 2 kb DNA fragment was identified which re-established producti on of autoinducer(s) and exoproducts in PAN067. From the nucleotide se quence of this fragment, two genes termed rhlR and rhll were identifie d, Rhll is responsible for autoinducer synthesis and shares 31% homolo gy with Lasl; RhlR has been previously identified in P. aeruginosa str ain DSM2659 as a regulator of rhamnolipid biosynthesis and shares 28% identity with LasR. These data provide clear evidence that multiple fa milies of quorum-sensing modulons interactively regulate gene expressi on in P. aeruginosa.