title: Evidence for a type III secretion system in Aeromonas salmonicida subsp. salmonicida.
abstract: Aeromonas salmonicida subsp. salmonicida, the etiological agent of furunculosis, is an important fish pathogen. We have screened this bacterium with a broad-host-range probe directed against yscV, the gene that encodes the archetype of a highly conserved family of inner membrane proteins found in every known type III secretion system. This has led to the identification of seven open reading frames that encode homologues to proteins functioning within the type III secretion systems of Yersinia species. Six of these proteins are encoded by genes comprising a virA operon. The A. salmonicida subsp. salmonicida yscV homologue, ascV, was inactivated by marker replacement mutagenesis and used to generate an isogenic ascV mutant. Comparison of the extracellular protein profiles from the ascV mutant and the wild-type strain indicates that A. salmonicida subsp. salmonicida secretes proteins via a type III secretion system. The recently identified ADP-ribosylating toxin AexT was identified as one such protein. Finally, we have compared the toxicities of the wild-type A. salmonicida subsp. salmonicida strain and the ascV mutant against RTG-2 rainbow trout gonad cells. While infection with the wild-type strain results in significant morphological changes, including cell rounding, infection with the ascV mutant has no toxic effect, indicating that the type III secretion system we have identified plays an important role in the virulence of this pathogen.
authors.affiliation: Institute of Veterinary Bacteriology. Centre for Fish and Wildlife Health, Institute of Animal Pathology, University of Berne, Laenggassstrasse 122, CH-3012 Berne, Switzerland.
authors.forename: Sarah E
authors.initials: SE
authors.lastname: Burr
authors.forename: Katja
authors.initials: K
authors.lastname: Stuber
authors.forename: Thomas
authors.initials: T
authors.lastname: Wahli
authors.forename: Joachim
authors.initials: J
authors.lastname: Frey
mesh_terms: D036002:ADP Ribose Transferases / Q000235:genetics / Q000378:metabolism*; D000333:Aeromonas / Q000235:genetics / Q000378:metabolism* / Q000472:pathogenicity; D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D002460:Cell Line; D003001:Cloning, Molecular; D004269:DNA, Bacterial; D008969:Molecular Sequence Data; D017686:Oncorhynchus mykiss; D009876:Operon / Q000502:physiology*; D017422:Sequence Analysis, DNA; D037521:Virulence Factors
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D037521:Virulence Factors; D036002:ADP Ribose Transferases