Molecular characterization of an Aeromonas salmonicida mutant with altered surface morphology and increased systemic virulence |
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Authors: | Brian Noonan Trevor J Trust |
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Institution: | Department of Biochemistry and Microbiology and Canadian Bacterial Diseases Network, University of Victoria, Victoria, British Columbia V8W 3P6, Canada. |
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Abstract: | The asoA gene of Aeromonas salmonicida is located approximately 7 kb downstream of the A-layer structural gene, vapA. A 6 kb Bam HI fragment containing aso A was cloned and marker-exchange mutagenesis using a kanamycin-resistance cassette was performed to generate an aso A mutation in the low-virulence strain A449L. When analysed by electron microscopy, the mutant A449L-MB exhibited an altered surface morphology. Strands and blebs of membranous material were observed protruding from the disorganized cell surface. This material was shown to contain lipopolysaccharide and A-layer subunit protein. The disorganization of the surface of A449L-IV1B had no apparent effect on virulence when the bacteria were administered to rainbow trout (Oncorhynchus mykiss) by bath Immersion. However, when administered by intraperitoneal injection, the mutant A449L-MB was found to exhibit significantly increased virulence. The predicted amino acid sequence of AsoA shows homology to a number of polytopic membrane proteins involved in translocation across the cytoplasmic membrane. |
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