Advancing the Quorum in <i>Pseudomonas aeruginosa</i> : MvaT and the Regulation of <i>N</i> -Acylhomoserine Lactone Production and Virulence Gene Expression

<jats:title>ABSTRACT</jats:title> <jats:p> <jats:italic>Pseudomonas aeruginosa</jats:italic> regulates the production of many exoproteins and secondary metabolites via a hierarchical quorum-sensing cascade through LasR and RhlR and their cognate signal molecules <jats:italic>N-</jats:italic> (3-oxododecanoyl)- <jats:sc>l</jats:sc> -homoserine lactone (3O-C12-HSL) and <jats:italic>N-</jats:italic> (butanoyl)- <jats:sc>l</jats:sc> -homoserine lactone (C4-HSL). In this study, we found that transcription of the quorum sensing-regulated genes <jats:italic>lecA</jats:italic> (coding for PA-IL lectin), <jats:italic>lasB</jats:italic> (coding for elastase), and <jats:italic>rpoS</jats:italic> appeared to be growth phase dependent and their expression could not be advanced to the logarithmic phase in cells growing in batch culture by the addition of exogenous C4-HSL and 3O-C12-HSL. To identify novel regulators responsible for this growth phase dependency, a <jats:italic>P. aeruginosa lecA</jats:italic> :: <jats:italic>lux</jats:italic> reporter strain was subjected to random transposon mutagenesis. A number of mutants affected in <jats:italic>lecA</jats:italic> expression were found that exhibited altered production of multiple quorum sensing-dependent phenotypes. While some mutations were mapped to new loci such as <jats:italic>clpA</jats:italic> and <jats:italic>mvaT</jats:italic> and a putative efflux system, a number of mutations were also mapped to known regulators such as <jats:italic>lasR</jats:italic> , <jats:italic>rhlR</jats:italic> , and <jats:italic>rpoS.</jats:italic> MvaT was identified as a novel global regulator of virulence gene expression, as a mutation in <jats:italic>mvaT</jats:italic> resulted in enhanced <jats:italic>lecA</jats:italic> expression and pyocyanin production. This mutant also showed altered swarming ability and production of the LasB and LasA proteases, 3O-C12-HSL, and C4-HSL. Furthermore, addition of exogenous 3O-C12-HSL and C4-HSL to the <jats:italic>mvaT</jats:italic> mutant significantly advanced <jats:italic>lecA</jats:italic> expression, suggesting that MvaT is involved in the growth phase-dependent regulation of the <jats:italic>lecA</jats:italic> gene. </jats:p>