The AlgT-Dependent Transcriptional Regulator AmrZ (AlgZ) Inhibits Flagellum Biosynthesis in Mucoid, Nonmotile Pseudomonas aeruginosa Cystic Fibrosis Isolates

Abstract

Pseudomonas aeruginosa is a microorganism associated with the disease cystic fibrosis. While environmental P. aeruginosa strains are generally nonmucoid and motile, isolates recovered from the cystic fibrosis lung frequently display a mucoid, nonmotile phenotype. This phenotypic conversion is mediated by the alternative sigma factor AlgT. Previous work has shown that repression of fleQ by AlgT accounts for the loss of flagellum biosynthesis in these strains. Here, we elucidate the mechanism involved in the AlgT-mediated control of fleQ. Electrophoretic mobility shift assays using purified AlgT and extracts derived from isogenic AlgT ؉ and AlgT ؊ strains revealed that AlgT inhibits fleQ indirectly. We observed that the AlgT-dependent transcriptional regulator AmrZ interacts directly with the fleQ promoter. To determine whether AmrZ functions as a repressor of fleQ, we mutated amrZ in the mucoid, nonmotile P. aeruginosa strain FRD1. Unlike the parental strain, the amrZ mutant was nonmucoid and motile. Complementation of the mutant with amrZ restored the mucoid, nonmotile phenotype. Thus, our data show that AlgT inhibits flagellum biosynthesis in mucoid, nonmotile P. aeruginosa cystic fibrosis isolates by promoting expression of AmrZ, which subsequently represses fleQ. Since fleQ directly or indirectly controls the expression of almost all flagellar genes, its repression ultimately leads to the loss of flagellum biosynthesis.

Signals, Regulatory Networks, and Materials That Build and Break Bacterial Biofilms

“…For example, in P. aeruginosa, the alternative sigma factor AlgT, which is a positive regulator of biofilm matrix synthesis, indirectly inhibits flagellar gene expression. AlgT promotes expression of the transcriptional regulator AmrZ, which then directly represses expression of FleQ, the master regulator of flagellar gene expression in this organism, thereby leading to loss of flagellar biosynthesis (316). Moreover, increases in both the synthesis of the biofilm matrix and the transcription of genes involved in the synthesis of the biofilm matrix are commonly observed in mutants lacking the flagellar structure, thus confirming the inverse relationship between motility and synthesis of the biofilm matrix.…”

Investigation of the algT operon sequence in mucoid and non-mucoid Pseudomonas aeruginosa isolates from 115 Scandinavian patients with cystic fibrosis and in 88 in vitro non-mucoid revertants

“…However, this is not the only mechanism of conversion to the nonmucoid phenotype; several alternative pathways have been suggested for the reversion to the non-mucoid state . It has been shown that the nonmucoid revertants due to mutations in algT become motile through upregulation of the flagella and this was considered an adaptive mechanism allowing P. aeruginosa to swim towards areas of higher oxygen concentration (Wyckoff et al, 2002;Tart et al, 2006). However, the nature of the non-mucoid isolates has not previously been investigated on a large number of P. aeruginosa isolates collected from the sputum of CF patients.…”

“…Congruent with the functions played by the s E in E. coli, AlgT is involved in the regulation of a number of other systems in P. aeruginosa, such as heat shock, osmotic protection and protection against reactive oxygen species Yu et al, 1995;Firoved et al, 2002). It has also been shown that AlgT represses flagellum biosynthesis in P. aeruginosa (Tart et al, 2006). Thus, the presence of uncontrolled AlgT in mucoid isolates interferes with the normal physiology of the cell and therefore the selective advantage of mucoid forms must be critical for the ability of this organism to persistently colonize and chronically infect CF patients .…”

The Pseudomonas aeruginosa Sensor Kinase KinB Negatively Controls Alginate Production through AlgW-Dependent MucA Proteolysis

“…The response regulator AlgR binds multiple sites within P algD and is required for P algD expression (21,38). Additionally, the alginate and motility regulator Z (AmrZ) also promotes activity at P algD (5,50). The NtrC family response regulator AlgB has recently been shown to bind at P algD and cause transcriptional activation (26).…”