Altered heat resistance in spores and vegetative cells of a mutant fromBacillus subtilis

The relationship between sporulation temperature and spore killing temperature is described.Bacillus subtilis YB886, grown and sporulated at 25°, 30°, 37°, and 45°C, produced spores having D₉₀ values of 63.5, 76.3, 89.0, and 106 min respectively. In addition, the vegetative cells of this strain also demonstrated resistance to heat killing when grown at elevated temperatures (D₅₀ of 26.6, 32.5, 39.0, and >50 min for cells grown at 25°, 30°, 37°, and 45°C). A transposon-generated mutant of strain YB886, designated as BUL786, which is missing a heat shock-induced protein (97 kDa) (Qoronfleh MW and Streips UN, BBRC, 138:526–532, 1986 and FEMS 1987), was tested for thermotolerance under similar conditions. The cells failed to respond to growth at high temperature by producing heat-resistant spores or vegetative cells. For strain BUL786 the D₉₀ of spores generated at 20°, 25°, 30°, 37°, and 45°C was 9.4, 11.3, 12.8, 14.1, and 20 min, respectively. Similarly, the D₅₀ of vegetative cells was 15, 16.8, 17.8, 19.0, and 22.3 min when the cells were grown at 20°, 25°, 30°, 37°, and 45°C. Also, sporulation of YB886 cells in the presence of cadmium chloride increased the D₉₀ values for the resulting spores (5µM CdCl₂ resulted in a D₉₀ of 160 min). Strain BUL786 failed to produce spores with any elevated D₉₀ when grown in the presence of CdCl₂.