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Integrated activities of two alternative sigma factors coordinate iron acquisition and uptake by Pseudomonas aeruginosa
Author(s) -
Edgar Rebecca J.,
Hampton Georgina E.,
Garcia G. Patricia Casas,
Maher Megan J.,
Perugini Matthew A.,
Ackerley David F.,
Lamont Iain L.
Publication year - 2017
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/mmi.13855
Subject(s) - biology , pyoverdine , sigma factor , pseudomonas aeruginosa , siderophore , gene , microbiology and biotechnology , regulation of gene expression , gene expression , genetics , bacteria , promoter
Summary Alternative sigma (σ) factors govern expression of bacterial genes in response to diverse environmental signals. In Pseudomonas aeruginosa σ PvdS directs expression of genes for production of a siderophore, pyoverdine, as well as a toxin and a protease. σ FpvI directs expression of a receptor for ferripyoverdine import. Expression of the genes encoding σ PvdS and σ FpvI is iron‐regulated and an antisigma protein, FpvR 20 , post‐translationally controls the activities of the sigma factors in response to the amount of ferripyoverdine present. Here we show that iron represses synthesis of σ PvdS to a far greater extent than σ FpvI . In contrast ferripyoverdine exerts similar effects on the activities of both sigma factors. Using a combination of in vivo and in vitro assays we show that σ FpvI and σ PvdS have comparable affinities for, and are equally inhibited by, FpvR 20 . Importantly, in the absence of ferripyoverdine the amount of FpvR 20 per cell is lower than the amount of σ FpvI and σ PvdS , allowing basal expression of target genes that is required to activate the signalling pathway when ferripyoverdine is present. This complex interplay of transcriptional and post‐translational regulation enables a co‐ordinated response to ferripyoverdine but distinct responses to iron.