The Novel Two-Component Regulatory System BfiSR Regulates Biofilm Development by Controlling the Small RNArsmZthrough CafA

Abstract

The formation of biofilms by the opportunistic pathogen Pseudomonas aeruginosa is a developmental process governed by a novel signal transduction system composed of three two-component regulatory systems (TCSs), BfiSR, BfmSR, and MifSR. Here, we show that BfiSR-dependent arrest of biofilm formation coincided with reduced expression of genes involved in virulence, posttranslational/transcriptional modification, and Rhl quorum sensing but increased expression of rhlAB and the small regulatory RNAs rsmYZ. Overexpression of rsmZ, but not rsmY, coincided with impaired biofilm development similar to inactivation of bfiS and retS. We furthermore show that BfiR binds to the 5 untranslated region of cafA encoding RNase G. Lack of cafA expression coincided with impaired biofilm development and increased rsmYZ levels during biofilm growth compared to the wild type. Overexpression of cafA restored ⌬bfiS biofilm formation to wild-type levels and reduced rsmZ abundance. Moreover, inactivation of bfiS resulted in reduced virulence, as revealed by two plant models of infection. This work describes the regulation of a committed biofilm developmental step following attachment by the novel TCS BfiSR through the suppression of sRNA rsmZ via the direct regulation of RNase G in a biofilm-specific manner, thus underscoring the importance of posttranscriptional mechanisms in controlling biofilm development and virulence.

Biofilm Development

“…In addition, sensor kinases and response regulators encoded by the bfiSR, bfmSR, and mifSR genes are evidently involved in the regulation of P. aeruginosa biofilm formation (39). Evidence was provided that the BfiSR system regulates biofilm formation by affecting synthesis of the CafA ribonuclease, which controls the level of the RsmZ sRNA (40). Moreover, the protein SagS was shown to contribute to the motile-to-sessile switch and act in concert with BfiSR to initiate P. aeruginosa biofilm formation (41).…”

SagS Contributes to the Motile-Sessile Switch and Acts in Concert with BfiSR To Enable Pseudomonas aeruginosa Biofilm Formation

“…Similarly to the Csr system in E. coli, sRNAs in Pseudomonas aeruginosa have been shown to play an important role in attachment, polysaccharide production, virulence, and quorum sensing (6,9,23,37,42,44). However, in contrast to the E. coli Csr system, the Rsm system in P. aeruginosa has not been linked to the modulation of cyclic di-GMP levels.…”

“…CsrABCD, originally identified as a system to regulate glycogen biosynthesis, controls carbon and secondary metabolism, biofilm formation, motility, and quorum sensing via destabilization of respective mRNA targets. Regulation of the activity of the RNA binding protein CsrA is mediated in part by the actions of the two noncoding small RNAs (sRNAs) CsrB and CsrC (24,25,28,46,59,64).Similarly to the Csr system in E. coli, sRNAs in Pseudomonas aeruginosa have been shown to play an important role in attachment, polysaccharide production, virulence, and quorum sensing (6,9,23,37,42,44). However, in contrast to the E. coli Csr system, the Rsm system in P. aeruginosa has not been linked to the modulation of cyclic di-GMP levels.…”

The Pseudomonas aeruginosa Two-Component Regulator AlgR Directly Activates rsmA Expression in a Phosphorylation-Independent Manner

“…The regulation of rsmZ is more complex than rsmY and includes regulators other than GacA (38,40,41). Primer extension analysis confirmed the location of the transcriptional start site in P. aeruginosa that was predicted from P. fluorescens (Fig.…”