The Crc protein participates in down‐regulation of the Lon gene to promote rhamnolipid production and rhl quorum sensing in Pseudomonas aeruginosa

Abstract

SummaryRhamnolipid acts as a virulence factor during Pseudomonas aeruginosa infection. Here, we show that deletion of the catabolite repression control (crc) gene in P. aeruginosa leads to a rhamnolipid-negative phenotype. This effect is mediated by the downregulation of rhl quorum sensing (QS). We discover that a disruption of the gene encoding the Lon protease entirely offsets the effect of crc deletion on the production of both rhamnolipid and rhl QS signal C4-HSL. Crc is unable to bind lon mRNA in vitro in the absence of the RNA chaperon Hfq, while Crc contributes to Hfq-mediated repression of the lon gene expression at a posttranscriptional level. Deletion of crc, which results in up-regulation of lon, significantly reduces the in vivo stability and abundance of the RhlI protein that synthesizes C4-HSL, causing the attenuation of rhl QS. Lon is also capable of degrading the RhlI protein in vitro. In addition, constitutive expression of rhlI suppresses the defects of the crc deletion mutant in rhamnolipid, C4-HSL and virulence on lettuce leaves. This study therefore uncovers a novel posttranscriptional regulatory cascade, CrcHfq/Lon/RhlI, for the regulation of rhamnolipid production and rhl QS in P. aeruginosa.

Pseudomonas aeruginosa Lon and ClpXP proteases: roles in linking carbon catabolite repression system with quorum-sensing system

“…However, it appears that some key players in CCR play important roles in the regulation of QS. For instance, the deletion of hfq in P. aeruginosa leads to reduced production of rhl QS signal C4-HSL (Sonnleitner et al 2006;Yang et al 2015). Similar effect was observed for the deletion of crc in P. aeruginosa (Yang et al 2015).…”

“…For instance, the deletion of hfq in P. aeruginosa leads to reduced production of rhl QS signal C4-HSL (Sonnleitner et al 2006;Yang et al 2015). Similar effect was observed for the deletion of crc in P. aeruginosa (Yang et al 2015). In addition, it has been reported that Crc modulates the pqs signaling in P. aeruginosa in a nutrient-dependent manner (Zhang et al 2013).…”

“…Takaya et al (2008) showed that Lon degrades the autoinducer synthase LasI in vivo (Takaya et al 2008). Yang et al (2015) showed that Lon degrades the autoinducer synthase RhlI in vitro and in vivo (Yang et al 2015). The degradation of either LasI or RhlI leads to the negative regulation of the rhl QS system (Yang et al 2015;Takaya et al 2008).…”

“…The degradation of either LasI or RhlI leads to the negative regulation of the rhl QS system (Yang et al 2015;Takaya et al 2008). Thus, it is not surprising that lon mutants overproduce the rhl QS signal C4-HSL and QS-regulated pyocyanin (Yang et al 2015;Takaya et al 2008).…”

“…The examples known to date suggest that the key regulatory component of P. aeruginosa CCR consists of Crc and Hfq proteins as well as the small RNA CrcZ (Sonnleitner and Blasi 2014). The Crc protein, when together with Hfq protein, promotes an inhibition in the translation of RNAs containing an AAnAAnAAn motif (catabolite activity motif, CA-motif) close to the translation start site via a mechanism is still not fully understood (Madhushani et al 2015;Sonnleitner and Blasi 2014;Yang et al 2015). The small RNA CrcZ contains several CA motifs and may antagonize Crc by sequestering Hfq, perhaps in combination with Crc (Rojo 2010;Poncet et al 2009;Gorke and Stulke 2008).…”