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J. Bacteriol., 05 1997, 3127-3132, Vol 179, No. 10
EC Pesci, JP Pearson, PC Seed and BH Iglewski
The production of several virulence factors by Pseudomonas aeruginosa is
controlled according to cell density through two quorum-sensing systems,
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 transcriptional activator
protein RhlR and of RhlI, which directs synthesis of the autoinducer PAI-2
(formerly referred to as factor 2). To study the interrelation between the
two P. aeruginosa quorum-sensing systems, we fused a lacZ reporter gene to
lasR, rhlR, and rhlA and monitored expression of these three genes under
various conditions. Our data indicate that lasR and rhlR are expressed in a
growth-dependent manner, with activation of each gene occurring during the
last half of log-phase growth. We also show that the las quorum- sensing
system controls the rhl quorum-sensing system in two ways. First, we found
that LasR and PAI-1 activated rhlR transcription. Second, we showed that
PAI-1 blocked PAI-2 from binding to RhlR, thereby inhibiting the expression
of rhlA. Our data thus indicate that the las system exerts two levels of
control on RhlR, transcriptional and posttranslational.
Copyright © 1997, American Society for Microbiology
Regulation of las and rhl quorum sensing in Pseudomonas aeruginosa
Department of Microbiology and Immunology, University of Rochester School of Medicine and Dentistry, New York 14642, USA.
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