σ Factor and Anti-σ Factor That Control Swarming Motility and Biofilm Formation in Pseudomonas aeruginosa

Abstract

Pseudomonas aeruginosa is capable of causing a variety of acute and chronic infections. Here, we provide evidence that sbrR (PA2895), a gene previously identified as required during chronic P. aeruginosa respiratory infection, encodes an anti-factor that inhibits the activity of its cognate extracytoplasmic-function factor, SbrI (PA2896). Bacterial two-hybrid analysis identified an N-terminal region of SbrR that interacts directly with SbrI and that was sufficient for inhibition of SbrI-dependent gene expression. We show that SbrI associates with RNA polymerase in vivo and identify the SbrIR regulon. In cells lacking SbrR, the SbrI-dependent expression of muiA was found to inhibit swarming motility and promote biofilm formation. Our findings reveal SbrR and SbrI as a novel set of regulators of swarming motility and biofilm formation in P. aeruginosa that mediate their effects through muiA, a gene not previously known to influence surface-associated behaviors in this organism. IMPORTANCEThis study characterizes a factor/anti-factor system that reciprocally regulates the surface-associated behaviors of swarming motility and biofilm formation in the opportunistic pathogen Pseudomonas aeruginosa. We present evidence that SbrR is an anti-factor specific for its cognate factor, SbrI, and identify the SbrIR regulon in P. aeruginosa. We find that cells lacking SbrR are severely defective in swarming motility and exhibit enhanced biofilm formation. Moreover, we identify muiA (PA1494) as the SbrI-dependent gene responsible for mediating these effects. SbrIR have been implicated in virulence and in responding to antimicrobial and cell envelope stress. SbrIR may therefore represent a stress response system that influences the surface behaviors of P. aeruginosa during infection.T he Gram-negative bacterium Pseudomonas aeruginosa is an opportunistic human pathogen notorious for being the principal cause of morbidity and mortality in cystic fibrosis (CF) patients (1). In patients with CF, chronic pulmonary colonization by P. aeruginosa leads to chronic inflammation, progressive loss of lung function, and eventually respiratory failure and death (1). P. aeruginosa is also the fifth leading cause of nosocomial infections overall in the United States and is the second most common cause of ventilator-associated pneumonia (VAP) and catheter-associated urinary tract infections (CAUTI) (2, 3). In patients with VAP or CAUTI, P. aeruginosa grows as a biofilm on endotracheal tubes and catheters, respectively (4-6). In addition, P. aeruginosa is thought to persist as a biofilm in the CF lung (7). P. aeruginosa biofilms are associated with chronic infection and exhibit increased antibiotic resistance and resistance to clearance by the immune system (8). Thus, the ability to form biofilms contributes significantly to the clinical burden of P. aeruginosa infection.In P. aeruginosa, growth as a biofilm is inversely regulated with a cooperative form of multicellular surface motility called swarming (9-12). Swarming motility is flagell...

An integrated model system to gain mechanistic insights into biofilm formation and antimicrobial resistance development inPseudomonas aeruginosaMPAO1

“…The differential proteomics data confirmed proteins known to play a role in biofilm formation and growth. These included MuiA, which inhibited swarming motility and enhanced biofilm formation (roles, that were validated in knockout strains) [40], and CbpD, for which higher protein expression had been observed in late phases of biofilm growth; accordingly, mutants displayed a lower amount of biofilm growth and exopolysaccharides (EPS) [41]. Inactivation studies showed that the gene encoding AcnA impaired biofilm formation and was required for microcolony formation [42], while increased expression of PilY1 repressed swarming and increased biofilm formation, as confirmed by knockout experiments [43].…”

“…Among the most significantly differentially expressed proteins (log 2 fold change (FC) of ≥ 1 or ≤ -1 and adjusted p value ≤ 0.05; see Methods) several candidates were identified that have previously been linked with a role in biofilm formation. These included MuiA (MPAO1_18330) [40], CbpD (MPAO1_21730) [41], AcnA (MPAO1_17965) [42] and PilY1 (MPAO1_24155) [43] (Fig. 5a, Table 3; see Discussion).…”

“…number of genes (55,62) or CDS (40,47) respectively, compared to our complete genome ( Supplementary Table 2).…”

Diversity of extracytoplasmic function sigma (σECF) factor‐dependent signaling in Pseudomonas

“…An σ ECF factor belonging to the ECF35 group, which is specific for Proteobacteria (Staroń et al , ), has been recently characterized in P. aeruginosa and named σ SbrI for swarming‐ and biofilm‐related due to its regulatory role in swarming motility and biofilm formation (McGuffie et al , ). DIAMOND BLASTp analyses shows that homologues to σ SbrI are present in P. protegens and P. fluorescens but not in P. putida and P. syringae (Dataset and Table ).…”

Identifying genetic determinants of complex phenotypes from whole genome sequence data

“…Likewise, sbrR is a factor involved in swimming ability [33], and would hence had been expected to be involved in the resistance to cephalosporins such as Ceftazidime, not the aminoglycoside Gentamicin (Table 3).…”