Evidence for Sigma Factor Competition in the Regulation of Alginate Production by Pseudomonas aeruginosa

Abstract

Alginate overproduction, or mucoidy, plays an important role in the pathogenesis of P. aeruginosa lung infection in cystic fibrosis (CF). Mucoid strains with mucA mutations predominantly populate in chronically-infected patients. However, the mucoid strains can revert to nonmucoidy in vitro through suppressor mutations. We screened a mariner transposon library using CF149, a non-mucoid clinical isolate with a misssense mutation in algU (AlgUA61V). The wild type AlgU is a stress-related sigma factor that activates transcription of alginate biosynthesis. Three mucoid mutants were identified with transposon insertions that caused 1) an overexpression of AlgUA61V, 2) an overexpression of the stringent starvation protein A (SspA), and 3) a reduced expression of the major sigma factor RpoD (σ70). Induction of AlgUA61V in trans caused conversion to mucoidy in CF149 and PAO1DalgU, suggesting that AlgUA61V is functional in activating alginate production. Furthermore, the level of AlgUA61V was increased in all three mutants relative to CF149. However, compared to the wild type AlgU, AlgUA61V had a reduced activity in promoting alginate production in PAO1ΔalgU. SspA and three other anti-σ70 orthologues, P. aeruginosa AlgQ, E. coli Rsd, and T4 phage AsiA, all induced mucoidy, suggesting that reducing activity of RpoD is linked to mucoid conversion in CF149. Conversely, RpoD overexpression resulted in suppression of mucoidy in all mucoid strains tested, indicating that sigma factor competition can regulate mucoidy. Additionally, an RpoD-dependent promoter (PssrA) was more active in non-mucoid strains than in isogenic mucoid variants. Altogether, our results indicate that the anti-σ70 factors can induce conversion to mucoidy in P. aeruginosa CF149 with algU-suppressor mutation via modulation of RpoD.

Coordinate Control of Virulence Gene Expression in Francisella tularensis Involves Direct Interaction between Key Regulators

“…SspA orthologs from several other bacteria, including Neisseria gonorrhoeae (16), Yersinia enterocolitica (17), Vibrio cholerae (18), enterohemorrhagic E. coli (20), and Pseudomonas aeruginosa (19), have also been implicated in regulating virulence gene expression. The mechanism by which SspA regulates the expression of virulence genes in these other organisms, however, is currently not well understood.…”

“…SspA orthologs in several other pathogens have also been shown to be important for virulence (16)(17)(18)(19)(20). F. tularensis genes encode two orthologs of SspA, one called MglA and another that is called SspA.…”

Knockout of Extracytoplasmic Function Sigma Factor ECF-10 Affects Stress Resistance and Biofilm Formation in Pseudomonas putida KT2440

“…One other possible explanation for the altered ttgABC gene expression in the ECF-10 knockout mutant could be sigma factor competition for the core RNA polymerase. This phenomenon has been shown to be responsible for altered regulation of genes or even whole pathways in various bacteria, including Pseudomonas aeruginosa and E. coli, among many others (54,55). Although the ECF sigma factor RpoT (ECF-12) was identified to control the ttgGHI efflux pump genes in P. putida DOT-T1E (56), so far, no sigma factor has been described to be involved in ttgABC transcription.…”

Structural alterations in Pseudomonas aeruginosa by zingerone contribute to enhanced susceptibility to antibiotics, serum and phagocytes

“…Alginate production in PAO1 and clinical isolates was significantly decreased after zingerone treatment. Alginate producing mucoid P. aeruginosa strains were typically associated with chronic pulmonary infections (Pedersen et al, 1992;Yin et al, 2013) and it has been shown that mucoid alginate-producing mutants of P. aeruginosa are major pathogens in patients with cystic fibrosis (Govan et al, 1992). Reversion of mucoid to non-mucoid phenotype is common in vitro and in vivo during the end-stage of CF disease that has been linked to environment pressure leading to decreased progression of infection (Yin et al, 2013).…”