title: Regulation of pga operon expression and biofilm formation in Actinobacillus pleuropneumoniae by sigmaE and H-NS.
abstract: Clinical isolates of the porcine pathogen Actinobacillus pleuropneumoniae often form adherent colonies on agar plates due to expression of an operon, pgaABCD, encoding a poly-beta-1,6-N-acetyl-D-glucosamine (PGA) extracellular matrix. The adherent colony phenotype, which correlates with the ability to form biofilms on the surfaces of polystyrene plates, is lost following serial passage in broth culture, and repeated passage of the nonadherent variants on solid media does not result in reversion to the adherent colony phenotype. In order to investigate the regulation of PGA expression and biofilm formation in A. pleuropneumoniae, we screened a bank of transposon mutants of the nonadherent serovar 1 strain S4074(T) and identified mutations in two genes, rseA and hns, which resulted in the formation of the adherent colony phenotype. In other bacteria, including the Enterobacteriaceae, H-NS acts as a global gene regulator, and RseA is a negative regulator of the extracytoplasmic stress response sigma factor sigma(E). Transcription profiling of A. pleuropneumoniae rseA and hns mutants revealed that both sigma(E) and H-NS independently regulate expression of the pga operon. Transcription of the pga operon is initiated from a sigma(E) promoter site in the absence of H-NS, and upregulation of sigma(E) is sufficient to displace H-NS, allowing transcription to proceed. In A. pleuropneumoniae, H-NS does not act as a global gene regulator but rather specifically regulates biofilm formation via repression of the pga operon. Positive regulation of the pga operon by sigma(E) indicates that biofilm formation is part of the extracytoplasmic stress response in A. pleuropneumoniae.
authors.affiliation: Department of Paediatrics, Imperial College London, St. Mary's Campus, London W21PG, United Kingdom.
authors.forename: Janine T
authors.initials: JT
authors.lastname: Bossé
authors.forename: Sunita
authors.initials: S
authors.lastname: Sinha
authors.forename: Ming-Shi
authors.initials: MS
authors.lastname: Li
authors.forename: Clíona A
authors.initials: CA
authors.lastname: O'Dwyer
authors.forename: John H E
authors.initials: JH
authors.lastname: Nash
authors.forename: Andrew N
authors.initials: AN
authors.lastname: Rycroft
authors.forename: J Simon
authors.initials: JS
authors.lastname: Kroll
authors.forename: Paul R
authors.initials: PR
authors.lastname: Langford
mesh_terms: D016977:Actinobacillus pleuropneumoniae / Q000235:genetics / Q000254:growth & development; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D018441:Biofilms / Q000254:growth & development; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D008969:Molecular Sequence Data; D009876:Operon / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid; D012808:Sigma Factor / Q000235:genetics / Q000378:metabolism*; D047071:beta-Glucans / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; C031908:H-NS protein, bacteria; D012808:Sigma Factor; D047071:beta-Glucans; C505465:poly-N-acetyl-1-6-glucosamine