Effects of heat shock on the thermotolerance, protein composition, and toxin production of Vibrio parahaemolyticus.

Vibrio parahaemolyticus, an important seafood-associated enteropathogen, usually encounters different adverse conditions in its native or food-processing environment, and the stresses resulting from these conditions may affect the survival of this pathogen and thus change its risk with regard to food hygiene. In this study, we investigated the thermotolerance of V. parahaemolyticus under sublethal heat shock and characterized this response by examining the changes in protein profiles and toxin production. Logarithmically grown cells heat shocked at 42 degrees C for 30 min were more resistant to thermal inactivation at 47 degrees C than were unshocked cells. After the 25 degrees C culture was heat shocked, 24 species of proteins were induced, while 13 species were inhibited, as indicated by polyacrylamide gel electrophoresis. DnaJ-, GroEL-, and GroES-like proteins with molecular sizes of 47, 62, and 12 kDa, respectively, were detected by immunoblotting with antibodies raised against the Escherichia coli proteins. During 1 to 8 h of heat shock, GroEL-like protein was produced in substantial amounts and was present in the periplasmic and extracellular fractions, while DnaJ- and GroES-like proteins were present mainly in the total cellular fraction. DnaK-like protein was not detected; nevertheless, the presence of the dnaK-like genetic element was revealed by Southern blotting. Production of thermostable direct hemolysin, the major virulence factor in V. parahaemolyticus, was enhanced in the cells heat shocked at 42 degrees C but not in those heat shocked at 37 degrees C.