A Three-Component Regulatory System Regulates Biofilm Maturation and Type III Secretion inPseudomonas aeruginosa

Abstract

ABSTRACTBiofilms are structured communities found associated with a wide range of surfaces. Here we report the identification of a three-component regulatory system required for biofilm maturation byPseudomonas aeruginosastrain PA14. A transposon mutation that altered biofilm formation in a 96-well dish assay originally defined this locus, which is comprised of genes for a putative sensor histidine kinase and two response regulators and has been designatedsadARS. Nonpolar mutations in any of thesadARSgenes result in biofilms with an altered mature structure but do not confer defects in growth or early biofilm formation, swimming, or twitching motility. After 2 days of growth under flowing conditions, biofilms formed by the mutants are indistinguishable from those formed by the wild-type (WT) strain. However, by 5 days, mutant biofilms appear to be more homogeneous than the WT in that they fail to form large and distinct macrocolonies and show a drastic reduction in water channels. We propose that thesadARSthree-component system is required for later events in biofilm formation on an abiotic surface. Semiquantitative reverse transcription-PCR analysis showed that there is no detectable change in expression of thesadARSgenes when cells are grown in a planktonic culture versus a biofilm, indicating that this locus is not itself induced during or in response to biofilm formation. DNA microarray studies were used to identify downstream targets of the SadARS system. Among the genes regulated by the SadARS system are those required for type III secretion. Mutations in type III secretion genes result in strains with enhanced biofilm formation. We propose a possible mechanism for the role that the SadARS system plays in biofilm formation.