REGULATION OF LAS AND RHL QUORUM SENSING IN PSEUDOMONAS-AERUGINOSA

The production of several virulence factors by Pseudomonas aeruginosa is controlled according to cell density through two quorum-sensing sys tems, las and rhl. The las system is comprised of the transcriptional activator protein LasR and of LasI, which directs the synthesis of the autoinducer PAI-1. Similarly, the rhl system consists of the transcri ptional activator protein RhlR and of RhlI, which directs synthesis of the autoinducer PAI-2 (formerly referred to as factor 2), To study th e interrelation between the two P. aeruginosa quorum-sensing systems, we fused a lacZ reporter gene to lasR, rhlR, and rhlA and monitored ex pression of these three genes under various conditions, Our data indic ate that lasR and rhlR are expressed in a growth-dependent manner, wit h activation of each gene occurring during the last half of log-phase growth, We also show that the las quorum-sensing system controls the r hl quorum-sensing system in two ways, First, we found that LasR and PA I-1 activated rhlR transcription, Second, we showed that PAI-I blocked PAI-2 from binding to RhlR, thereby inhibiting the expression of rhlA , Our data thus indicate that the [as system exerts two levels of cont rol on RhlR, transcriptional and posttranslational.