title: The non-pathogenic Escherichia coli strain W secretes SslE via the virulence-associated type II secretion system beta.
abstract: BACKGROUND
  Many pathogenic E. coli strains secrete virulence factors using type II secretory systems, homologs of which are widespread in Gram-negative bacteria. Recently, the enteropathogenic Escherichia coli strain E2348/69 was shown to secrete and surface-anchor SslE, a biofilm-promoting virulence factor, via a type II secretion system. Genes encoding SslE and its associated secretion system are conserved in some non-pathogenic E. coli, including the commonly-used W (Waksman) strain.
  
  
  RESULTS
  We report here that E. coli W uses its type II secretion system to export a cognate SslE protein. SslE secretion is temperature- and nutrient-dependent, being robust at 37°C in rich medium but strongly repressed by lower temperatures or nutrient limitation. Fusing either of two glycosyl hydrolases to the C-terminus of SslE prevented it from being secreted or surface-exposed. We screened mutations that inactivated the type II secretion system for stress-related phenotypes and found that inactivation of the secretion system conferred a modest increase in tolerance to high concentrations of urea. Additionally, we note that the genes encoding this secretion system are present at a hypervariable locus and have been independently lost or gained in different lineages of E. coli.
  
  
  CONCLUSIONS
  The non-pathogenic E. coli W strain shares the extracellular virulence factor SslE, and its associated secretory system, with pathogenic E. coli strains. The pattern of regulation of SslE secretion we observed suggests that SslE plays a role in colonization of mammalian hosts by non-pathogenic as well as pathogenic E. coli. Our work provides a non-pathogenic model system for the study of SslE secretion, and informs future research into the function of SslE during host colonization.
authors.affiliation: Great Lakes Bioenergy Research Center, University of Wisconsin-Madison, Madison, WI, USA.
authors.forename: Mark S
authors.initials: MS
authors.lastname: Decanio
authors.forename: Robert
authors.initials: R
authors.lastname: Landick
authors.forename: Rembrandt J F
authors.initials: RJ
authors.lastname: Haft
mesh_terms: D058947:Bacterial Secretion Systems; D004926:Escherichia coli / Q000378:metabolism / Q000502:physiology*; D029968:Escherichia coli Proteins / Q000378:metabolism*; D037521:Virulence Factors / Q000378:metabolism
chemical_list: D058947:Bacterial Secretion Systems; D029968:Escherichia coli Proteins; C583861:SslE protein, E coli; D037521:Virulence Factors