DAO 36:29-35 (1999)  -  doi:10.3354/dao036029

Elevated temperature treatment as a novel method for decreasing p57 on the cell surface of Renibacterium salmoninarum

Jon D. Piganelli*,**, Gregory D. Wiens*,***, Stephen L. Kaattari****

Department of Microbiology and Center for Salmon Disease Research, Oregon State University, Corvallis, Oregon 97331, USA
*J. Piganelli and G. Wiens contributed equally to this manuscript.
Present addresses: **Barbara Davis Center for Childhood Diabetes and Department of Immunology, University of Colorado Health Sciences Center, Denver, Colorado 80262, USA. E-mail:
***Department of Molecular Microbiology and Immunology, Oregon Health Sciences University, Portland, Oregon 97219, USA
****School of Marine Science, Virginia Institute of Marine Science, The College of William & Mary, Gloucester Point, Virginia 23062, USA

ABSTRACT: Renibacterium salmoninarum is a Gram-positive diplo-bacillus and the causative agent of bacterial kidney disease, a prevalent disease of salmonid fish. Virulent isolates of R. salmoninarum have a hydrophobic cell surface and express the 57-58 kDa protein (p57). Here we have investigated parameters which effect cell hydrophobicity and p57 degradation. Incubation of R. salmoninarum cells at 37°C for >4 h decreased cell surface hydrophobicity as measured by the salt aggregation assay, and decreased the amount of cell associated p57. Incubation of cells at lower temperatures (22, 17, 4 or -20°C) for up to 16 h did not reduce hydrophobicity or the amount of cell associated p57. Both the loss of cell surface hydrophobicity and the degradation of p57 were inhibited by pre-incubation with the serine protease inhibitor phenylmethylsulfonyl fluoride (PMSF). Cell surface hydrophobicity was specifically reconstituted by incubation with extracellular protein (ECP) concentrated from culture supernatant and was correlated with the reassociation of p57 onto the bacterial cell surface as determined by western blot and total protein stain analyses. The ability of p57 to reassociate suggests that the bacterial cell surface is not irreversibly modified by the 37°C treatment and that p57 contributes to the hydrophobic nature of R. salmoninarum. In summary, we describe parameters effecting the removal of the p57 virulence factor and suggest the utility of this modification for generating a whole cell vaccine against bacterial kidney disease.

KEY WORDS: Renibacterium salmoninarum · Bacterial kidney disease · p57

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