Role of Cell Surface Signaling in Proteolysis of an Alternative Sigma Factor in<i>Pseudomonas aeruginosa</i>

Spencer, Matthew R.; Beare, Paul A.; Lamont, Iain L.

doi:10.1128/jb.01998-07

Cited by 19 publications

(30 citation statements)

References 42 publications

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“…However, in some cases, ECF factors exhibit reduced activity and abundance in the absence of their cognate anti-factors, which are thought to stabilize and protect the factor from degradation (39,40). Alternatively, anti-factors can also promote the proteolysis of their cognate factors (41). A comparison of the abundance of SbrI with a C-terminal VSV-G epitope tag (SbrI-V) in WT and ⌬sbrR mutant cells revealed that SbrI-V (synthesized from its native locus) is more abundant in the absence of SbrR (Fig.…”

Section: Resultsmentioning

confidence: 99%

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

2016

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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...

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Section: Resultsmentioning

confidence: 99%

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

2016

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“…When pyoverdine is not available, FpvI and PvdS activity is inhibited by the sigma regulator protein FpvR. FpvR is thought to sequester FpvI and PvdS at the inner membrane and also renders PvdS susceptible to proteolysis (Lamont et al ., 2002; Beare et al ., 2003; Spencer et al ., 2008; Tiburzi et al ., 2008). The binding of pyoverdine to FpvA results in a signal being transferred through a periplasmic domain of FpvA to FpvR (Shen et al ., 2002; James et al ., 2005).…”

Section: Introductionmentioning

confidence: 99%

Differential proteolysis of sigma regulators controls cell‐surface signalling in Pseudomonas aeruginosa

Draper

Martin

Beare

et al. 2011

Molecular Microbiology

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SummaryCell-surface signalling systems are widespread in Gram-negative bacteria. In these systems gene expression occurs following binding of a ligand, commonly a siderophore, to a receptor protein in the outer membrane. The receptor interacts with a sigma regulator protein that extends from the periplasm into the cytoplasm to control the activity of a cognate sigma factor. The mechanisms of signal transduction in cell-surface signalling systems have not been determined. Here we investigate signal transduction in the pyoverdine, ferrichrome and desferrioxamine siderophore systems of Pseudomonas aeruginosa. When pyoverdine is present the sigma regulator FpvR undergoes complete proteolysis resulting in activation of two sigma factors PvdS and FpvI and expression of genes for pyoverdine synthesis and uptake. When pyoverdine is absent subfragments of FpvR inhibit PvdS and FpvI. Similarly, subfragments of the sigma regulators FoxR and FiuR are formed in the absence of desferrioxamine and ferrichrome. These are much less abundant when the siderophores are present and downstream gene expression takes place. In all three systems RseP (MucP/YaeL) is required for complete proteolysis of the sigma regulator and sigma factor activity. These findings indicate that regulated proteolysis is a general mechanism for signal transduction in cell-surface signalling.

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“…2), but the reason for this is not known. Proteolysis of PvdS occurs in the absence of pyoverdinemediated signaling (49). We therefore tested whether proteolysis of PvdS would occur in strains with the altered TonB box or in the tonB1 mutants.…”

Section: Resultsmentioning

confidence: 99%

“…Western analysis of PvdS. Western analysis was carried out as described previously (49). Briefly, cultures were grown to late exponential phase in King's B medium with or without pyoverdine (60 M).…”

Section: Methodsmentioning

confidence: 99%

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Role of TonB1 in Pyoverdine-Mediated Signaling inPseudomonas aeruginosa

Shirley

Lamont

2009

J Bacteriol

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Pyoverdines are siderophores secreted by Pseudomonas aeruginosa. Uptake of ferripyoverdine in P. aeruginosa PAO1 occurs via the FpvA receptor protein and requires the energy-transducing protein TonB1. Interaction of (ferri)pyoverdine with FpvA activates pyoverdine gene expression in a signaling process involving the cytoplasmic-membrane-spanning anti-sigma factor FpvR and the sigma factor PvdS. Here, we show that mutation of a region of FpvA that interacts with TonB1 (the TonB box) prevents this signaling process, as well as inhibiting bacterial growth in the presence of the iron-chelating compound ethylenediamine-di(o-hydroxyphenylacetic acid). Signaling via wild-type FpvA was also eliminated in strains lacking TonB1 but was unaffected in strains lacking either (or both) of two other TonB proteins in P. aeruginosa, TonB2 and TonB3. An absence of pyoverdine-mediated signaling corresponded with proteolysis of PvdS. These data show that interactions between FpvA and TonB1 are required for (ferri)pyoverdine signal transduction, as well as for ferripyoverdine transport, consistent with a mechanistic link between the signaling and transport functions of FpvA.Pseudomonas aeruginosa is an opportunistic pathogen that is able to cause severe infections in patients with cystic fibrosis and in immunocompromised individuals, such as burn victims. Under conditions of iron limitation, P. aeruginosa secretes an iron-scavenging compound (siderophore) called pyoverdine. Ferripyoverdine is transported back into the bacteria by an outer membrane (OM) receptor protein, FpvA. The transport of ferripyoverdine via FpvA requires energy provided by a TonB complex (36,42,50). TonB is an energy-transducing protein that couples the energy of the cytoplasmic membrane (CM) to a variety of OM receptors required for the import of ferrisiderophores and other molecules. TonB acts in a complex with two CM-associated proteins, ExbB and ExbD, both of which are required for full TonB function (5, 37). The TonBExbB-ExbD complex has been identified in many gram-negative bacterial species and is thought to be a conserved mechanism for energy transduction to OM receptor proteins (31). TonBdependent receptors contain a conserved protein motif known as the TonB box (5). Direct interaction between TonB and the TonB box has been demonstrated for several 26,33,35,47). Mutations of the TonB box, particularly mutations that are likely to affect the secondary structure, can result in a TonB-uncoupled phenotype characterized by loss of TonB-dependent functions (ferrisiderophore transport) with no loss of TonB-independent functions, such as internalization of bacteriophage (37).The P. aeruginosa PAO1 genome contains three tonB genes, tonB1 (PA5531) (36), tonB2 (PA0197) (55), and tonB3 (PA0406) (20), encoding proteins of 342, 270, and 319 amino acids (aa), respectively. The TonB1 and TonB2 amino acid sequences display 31% identity over a section of 187 aa, but otherwise, the three PAO1 TonB proteins show similarity (30 to 40% aa identity) to each other only over s...

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Role of Cell Surface Signaling in Proteolysis of an Alternative Sigma Factor inPseudomonas aeruginosa

Cited by 19 publications

References 42 publications

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

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

Differential proteolysis of sigma regulators controls cell‐surface signalling in Pseudomonas aeruginosa

Role of TonB1 in Pyoverdine-Mediated Signaling inPseudomonas aeruginosa

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