Characterization of a <i>Pseudomonas aeruginosa</i> gene cluster involved in pilus biosynthesis and twitching motility: sequence similarity to the chemotaxis proteins of enterics and the gliding bacterium <i>Myxococcus xanthus</i>

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<jats:title>Summary</jats:title><jats:p>The type 4 pill of <jats:italic>Pseudomonas aeruginosa are</jats:italic> important cell‐associated virulence factors that play a crucial role in mediating (i) bacterial adherence to, and colonization of, mucosal surfaces, (ii) a novel mode of fiagetia‐independent surface translocation known as‘twitching motility, and (iii) the initial stages of the infection process for a number of bacteriophages. A new set of loci involved in pilus biogenesis and twitching motility was identified based on the ability of DNA sequences downstream of the <jats:italic>pilG</jats:italic> gene to complement the non‐piliated <jats:italic>(pil)</jats:italic> strain, PAO6609. Sequence analysis of a 3.2 kb region directly downstream of <jats:italic>pilG</jats:italic> revealed the presence of three genes, which have been designated <jats:italic>pilH, pill</jats:italic>, and <jats:italic>pilJ.</jats:italic> The predicted translation product of the <jats:italic>pilH</jats:italic> gene (13 272 Da), like PilG, exhibits significant amino acid identity with the enteric single‐domain response regulator CheY. The putative Pili protein (19933 Da) is 28% identical to the FrzA protein, a CheW homologue of the gliding bacterium <jats:italic>Myxococcus xanthus</jats:italic>, and the PMJ protein (72 523 Da) is 26% identical to the enteric methyl‐accepting chemotaxis protein (MCP) Tsr. Mutants containing insertions in <jats:italic>pill</jats:italic> and <jats:italic>pilJ</jats:italic> were severely impaired in their ability to produce pili and did not translocate across solid surfaces. The <jats:italic>pilH</jats:italic> mutant remained capable of pilus production and twitching motility, but displayed an altered motility pattern characterized by the presence of many doughnut‐shaped swirls. Each of these <jats:italic>pil</jats:italic> mutants, however, produced zones that were at least as large as the parent in flagellar‐mediated swarm assays. The sequence similarities between the putative <jats:italic>pilG, H, I</jats:italic> and J gene products and several established chemotaxis proteins, therefore, lend strong support to the hypothesis that these proteins are part of a signal‐transduction network that controls <jats:italic>P. aeruginosa</jats:italic> pilus biosynthesis and twitching motility.</jats:p>

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