The Alternative Sigma Factor AlgT RepressesPseudomonas aeruginosaFlagellum Biosynthesis by Inhibiting Expression offleQ

Abstract

Pseudomonas aeruginosa poses a serious risk in individuals suffering from cystic fibrosis (CF). Strains colonizing the CF lung are generally motile but frequently convert to a nonmotile phenotype as the disease progresses. In many cases, this is coordinately regulated with the overproduction of the exopolysaccharide alginate. Both the expression of alginate (mucoidy) and the loss of flagellum synthesis may provide the bacterium with a selective advantage in the CF lung. Previously published data showed that the regulation of alginate production and flagellum biosynthesis in the CF isolate FRD1 is inversely controlled by the alternative sigma factor AlgT. In this study, we observed that in CF isolates, the mucoid and the nonmotile phenotypes occur predominantly together. Using microarrays, we compared the transcriptomes of isogenic AlgT ؉ and AlgT ؊ P. aeruginosa and discovered that AlgT significantly downregulated the majority of flagellar genes. A pronounced inhibitory effect was observed in several genes essential for proper flagellum expression, including fleQ, which encodes an essential flagellar regulator. The microarray data were confirmed by reverse transcriptase PCR analysis and promoter fusion assays in isogenic AlgT ؉ and AlgT ؊ strains. Transmission electron microscopy, motility assays, and Western blots showed that ectopic expression of FleQ in mucoid, nonmotile CF isolates restored flagellum biosynthesis and motility. Together, these data show that AlgT mediates the negative control of flagellum expression by inhibiting the expression of the flagellar regulator fleQ.

Regulation of bacterial virulence gene expression by cell envelope stress responses

“…Notably, microarrays revealed that AlgU downregulated several genes involved in the transcriptional control of flagella and the type IV pilus. 60,68 This is consistent with most isolates from the lungs of long-term colonized CF patients being non-motile. 69 Although the flagellum is important for attachment and the establishment of infection, its production and use requires a great deal of energy.…”

The alternative sigma factor AlgT, but not alginate synthesis, promotes in planta multiplication of Pseudomonas syringae pv. glycinea

“…In P. aeruginosa it was shown that AlgT directs transcription of a large set of virulence determinants or toxic factors (Firoved et al, 2002;Firoved & Deretic, 2003) and of the gene encoding the main heat-shock factor RpoH (Schurr & Deretic, 1997). Microarray analysis revealed that AlgT exerts broad-range regulatory effects on approximately 6 % of the P. aeruginosa genome, with alginate and flagellar genes accounting for only one-fifth of AlgT-regulated genes (Tart et al, 2005). AlgT was found to be essential for the tolerance of a P. fluorescens biocontrol strain towards desiccation and osmotic stress (Schnider-Keel et al, 2001).…”

Pseudomonas aeruginosa – Pathogenesis and Pathogenic Mechanisms

“…Non-flagellated mutants are often isolated from chronic infections in CF patients (Mahenthiralingam, Campbell, & Speert, 1994) due to the repressor activity of AlgT, which acts on the FleQ regulator (Tart, Wolfgang, & Wozniak, 2005). The loss of flagella in these isolates is believed to be useful for the invasion of the host immune system.…”

“…The mucoid form of P. aeruginosa is associated with 90% of P. aeruginosa CF infections compared to only 2% of P. aeruginosa non-CF infections (Doggett, 1969;Doggett, Harrison, & Carter, 1971). This phenotype is often coordinately regulated with a loss of flagella by the alternative sigma factor AlgT (Tart, Wolfgang, & Wozniak, 2005). The loss of flagella causes not only loss of motility, but also decreased activation of host inflammatory mediators (Cobb, Mychaleckyj, Wozniak, & Lopez-Boado, 2004).…”