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Title

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

Authors

Yeshi Yin, Marshall UniversityFollow
T. Ryan Withers, Marshall UniversityFollow
Xin Wang
Hongwei D. Yu, Marshall UniversityFollow

Document Type

Article

Publication Date

8-2013

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(AlgU^A61V). 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 AlgU^A61V, 2) an overexpression of the stringent starvation protein A (SspA), and 3) a reduced expression of the major sigma factor RpoD (σ⁷⁰). Induction of AlgU^A61V in trans caused conversion to mucoidy in CF149 and PAO1DalgU, suggesting that AlgU^A61V is functional in activating alginate production. Furthermore, the level of AlgU^A61V 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 (P_ssrA) 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.

Comments

The version of record is available online from the publisher at http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0072329.

Copyright © 2013 the authors.

Recommended Citation

Yin Y, Withers TR, Wang X, Yu HD (2013) Evidence for Sigma Factor Competition in the Regulation of Alginate Production by Pseudomonas aeruginosa. PLoS ONE 8(8): e72329. doi:10.1371/journal.pone.0072329