title: Molecular analysis of an A-protein secretion mutant of Aeromonas salmonicida reveals a surface layer-specific protein secretion pathway.
abstract: The Aeromonas salmonicida Tn5 mutant, A449-TM1, is unable to secrete the surface layer protein (A-protein) through the outer membrane. Immunogold labeling of thin sections of A449-TM1, with polyclonal antisera against the A-protein, showed the accumulation of large quantities of A-protein in an enlarged periplasm. The majority of the labeled A-protein could be seen at the poles of the cells. The ability of A449-TM1 to secrete other extracellular proteins such as hemolysin and protease was not impaired by the Tn5 insertion, which indicates that the mutation in A449-TM1 interferes with a secretion pathway specifically for the translocation of the A-protein through the outer membrane. The mutant, A449-TM1, was shown to be avirulent for fish. A cosmid clone from a gene library of A449-TM1, which contains the Tn5 insertion from the chromosome, was used to identify a 1.4 kb SaII/ClaI fragment from immediately adjacent to the Tn5 insertion. This fragment was used to identify and clone a 4 kb HindIII fragment from a chromosomal DNA digest from the wild-type strain, A449. DNA sequence analysis of this clone identified an open reading frame (ORF) of 1656 bp. The deduced product of this ORF showed sequence similarity to a family of ATP-binding secretion proteins, but appeared to be phylogenetically distinct from these proteins, consistent with its participation in a secretory pathway specific for surface layer protein.
authors.affiliation: Department of Biochemistry and Microbiology, University of Victoria, B.C., Canada.
authors.forename: B
authors.initials: B
authors.lastname: Noonan
authors.forename: T J
authors.initials: TJ
authors.lastname: Trust
mesh_terms: D000333:Aeromonas / Q000235:genetics / Q000378:metabolism* / Q000472:pathogenicity; D000595:Amino Acid Sequence; D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism*; D001692:Biological Transport / Q000235:genetics; D002352:Carrier Proteins / Q000235:genetics*; D003001:Cloning, Molecular; D005798:Genes, Bacterial / Q000235:genetics*; D005816:Genetic Complementation Test; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D016296:Mutagenesis; D017684:Oncorhynchus kisutch / Q000382:microbiology; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity; D014774:Virulence / Q000235:genetics; D037521:Virulence Factors
chemical_list: C093404:ApsE protein, Aeromonas salmonicida; D001426:Bacterial Proteins; D002352:Carrier Proteins; D008562:Membrane Glycoproteins; D037521:Virulence Factors