Vegetative cells of Clostridium perfringens enterotoxigenic strains NCTC 8679, NCTC 8238. and H6 were grown at 37 degrees C followed by a 60-min exposure to 28 degrees C or 46 degrees C. D10-values, as a measure of thermal resistance at 60 degrees C, were significantly lower for 28 degrees C exposures as compared with cultures given 37 and 46 degrees C exposures. Following refrigeration at 4 degrees C for 24 h, D10-values for the 37 and 46 degrees C samples could not be differentiated from 28 degrees C samples. Western immunoblot analyses of lysates from heat-adapted cells also detected the increased expression of proteins reacting with antiserum directed against the molecular chaperonins from Escherichia coli; GroEL, DnaJ, and the small acid soluble protein from Bacillus subtilis, SspC. Differential scanning calorimetry (DSC) identified thermal transitions corresponding to ribosomal protein denaturations at 72.1 +/- 0.5 degrees C. Any cellular heat adaptations in the DSC profiles were lost following refrigeration for several days to simulate minimally processed food storage conditions. Further analyses of high-speed pellets from crude cell extract fractions using two-dimensional gel electrophoresis detected the differential gene expression of at least four major proteins in heat-adapted vegetative cells of C. perfringens. N-terminal amino acid analyses identified two of the proteins as glyceraldehyde 3-phosphate dehydrogenase and rubrerythrin. Both appear to have roles in this anaerobe under stressful conditions.