RsaL provides quorum sensing homeostasis and functions as a global regulator of gene expression in Pseudomonas aeruginosa

Abstract

SummaryThe quorum sensing (QS) signalling system of Pseudomonas aeruginosa controls many important functions, including virulence. Although the production of the QS signal molecule N-3-oxo-dodecanoylhomoserine lactone (3OC12-HSL) is positively autoregulated, its concentration reaches a steady level long before stationary phase. The RsaL protein represses transcription of the lasI signal synthase gene, and thus reduces QS signal production. We show that RsaL binds simultaneously with LasR to the rsaL-lasI bidirectional promoter thereby preventing the LasR-dependent activation of both genes. In an rsaL mutant, 3OC12-HSL production continues to increase throughout growth. Thus RsaL provides homeostasis by functioning in opposition to LasR and limiting 3OC12-HSL production to a physiological concentration. Furthermore, transcription profiling revealed that RsaL regulates 130 genes independent of its effect on QS signal molecule production, including genes involved in virulence. We show that RsaL can repress pyocyanin and hydrogen cyanide virulence genes in two ways: directly, by binding to their promoters, and indirectly, by decreasing levels of the signals for their QS signal-dependent transcription. These investigations highlight the importance of RsaL as a global regulator of P. aeruginosa physiology that provides a counterbalance to 3OC 12-HSLdependent gene activation via multiple mechanisms.

Negative regulation of bacterial quorum sensing tunes public goods cooperation

“…QteE and QscR dampened the expression of QS target genes after transition to the 'on' state, providing homeostatic regulation. A similar mechanism balances 3OC12-HSL production in P. aeruginosa: RsaL, another QS repressor, is activated by LasR and directly represses lasI transcription (Rampioni et al, 2006;Rampioni et al, 2007). Thus, the initial positive feedback mechanism in QS, autoinduction, is tightly coupled with and immediately followed by multiple negative feedback mechanisms that confine the metabolic cost of public goods production.…”

Global Regulatory Pathways and Cross-talk ControlPseudomonas aeruginosaEnvironmental Lifestyle and Virulence Phenotype

“…The rsaL and lasI genes are divergently transcribed and coregulated. LasR binding to the lasI-rsaL intergenic region triggers transcription of both genes Schuster, 2004b), while RsaL binding results in repression of lasI-rsaL transcription (Rampioni, 2007), ensuring tight control of this negative regulator. Rampioni et al (2007) demonstrated that while RsaL and LasR are capable of binding simultaneously to the intergenic region; repression by RsaL supersedes LasR-mediated activation (Rampioni, 2007).…”

“…LasR binding to the lasI-rsaL intergenic region triggers transcription of both genes Schuster, 2004b), while RsaL binding results in repression of lasI-rsaL transcription (Rampioni, 2007), ensuring tight control of this negative regulator. Rampioni et al (2007) demonstrated that while RsaL and LasR are capable of binding simultaneously to the intergenic region; repression by RsaL supersedes LasR-mediated activation (Rampioni, 2007). RsaL appears to be a global regulator, controlling ~130 genes independent of its effect on lasI expression (Rampioni, 2007), including genes whose products are involved in antibiotic resistance and biofilm formation in P. aeruginosa (Rampioni, 2009).…”

“…Rampioni et al (2007) demonstrated that while RsaL and LasR are capable of binding simultaneously to the intergenic region; repression by RsaL supersedes LasR-mediated activation (Rampioni, 2007). RsaL appears to be a global regulator, controlling ~130 genes independent of its effect on lasI expression (Rampioni, 2007), including genes whose products are involved in antibiotic resistance and biofilm formation in P. aeruginosa (Rampioni, 2009). Evidence for rsaL upregulation was found in P. aeruginosa RNA harvested from sputum samples obtained from chronically infected CF patients, suggesting that RsaL plays a role in C12-HSL homeostatic control during chronic infection (Son, 2007).…”

Pseudomonas Aeruginosa AmpR Transcriptional Regulatory Network

“…Transcriptome analysis indicates that Vfr affects the expression of more than 100 genes in P. aeruginosa including T3SS genes (29). RsaL (PA1431), which is divergently transcribed from the lasI gene, encodes an autoregulating repressor that inhibits not only lasI transcription, but also genes involved in pyocyanin and cyanide synthesis (372,373). Interestingly, RsaL repression is dominant over 3-oxo-C12-HSL:LasR activation of lasI to counteract the positive feedback loop (372).…”