title: Surface protein composition of Aeromonas hydrophila strains virulent for fish: identification of a surface array protein.
abstract: The surface protein composition of members of a serogroup of Aeromonas hydrophila which exhibit high virulence for fish was examined. Treatment of whole cells of representative strain A. hydrophila TF7 with 0.2 M glycine buffer (pH 4.0) resulted in the release of sheets of a tetragonal surface protein array. Sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis analysis showed that this sheet material was composed primarily of a protein of apparent molecular weight 52,000 (52K protein). A 52K protein was also the predominant protein in glycine extracts of other members of the high-virulence serogroup. Immunoblotting with antiserum raised against formalinized whole cells of A. hydrophila TF7 showed the 52K S-layer protein to be the major surface protein antigen, and impermeant Sulfo-NHS-Biotin cell surface labeling showed that the 52K S-layer protein was the only protein accessible to the Sulfo-NHS-Biotin label and effectively masked underlying outer membrane (OM) proteins. In its native surface conformation the 52K S-layer protein was only weakly reactive with a lactoperoxidase 125I surface iodination procedure. A UV-induced rough lipopolysaccharide (LPS) mutant of TF7 was found to produce an intact S layer, but a deep rough LPS mutant was unable to maintain an array on the cell surface and excreted the S-layer protein into the growth medium, indicating that a minimum LPS oligosaccharide size was required for A. hydrophila S-layer anchoring. The 52K S-layer protein exhibited hear-dependent SDS-solubilization behavior when associated with OM, but was fully solubilized at all temperatures after removal from the OM, indicating a strong interaction of the S layer with the underlying OM. The native S layer was permeable to 125I in the lactoperoxidase radiolabeling procedure, and two major OM proteins of molecular weights 30,000 and 48,000 were iodinated. The 48K species was a peptidoglycan-associated, transmembrane protein which exhibited heat-modifiable SDS solubilization behaviour characteristic of a porin protein. A 50K major peptidoglycan-associated OM protein which was not radiolabeled exhibited similar SDS heat modification characteristics and possibly represents a second porin protein.
authors.affiliation: Department of Biochemistry and Microbiology, University of Victoria, British Columbia, Canada.
authors.forename: J S
authors.initials: JS
authors.lastname: Dooley
authors.forename: T J
authors.initials: TJ
authors.lastname: Trust
mesh_terms: D000333:Aeromonas / Q000737:chemistry* / Q000276:immunology / Q000472:pathogenicity / Q000648:ultrastructure; D000818:Animals; D000942:Antigens, Bacterial / Q000032:analysis; D000954:Antigens, Surface / Q000032:analysis; D001425:Bacterial Outer Membrane Proteins / Q000032:analysis*; D002462:Cell Membrane / Q000737:chemistry / Q000648:ultrastructure; D002499:Centrifugation, Density Gradient; D004591:Electrophoresis, Polyacrylamide Gel; D005399:Fishes / Q000382:microbiology; D007118:Immunoassay; D007124:Immunoenzyme Techniques; D008854:Microscopy, Electron; D008970:Molecular Weight; D014774:Virulence
chemical_list: D000942:Antigens, Bacterial; D000954:Antigens, Surface; D001425:Bacterial Outer Membrane Proteins