Identification of a germination system involved in the heat injury of Bacillus subtilis spores.

Bacillus subtilis A spores were injured by exposure to heat treatments of 110 to 132 C. Injury was demonstrated by the inability to form colonies on fortified nutrient agar (FNA) unless the medium was supplemented with CaCl(2) and Na(2) dipicolinate (CNA). A preliminary heat treatment fully heat-activated the spores, was not lethal, and did not prevent injury by subsequent secondary heat treatment. Exposure of heat-activated spores to 122 C reduced germination in FNA. The primary germination agents in FNA were identified, and a defined germination medium of glucose, NaCl, l-alanine, and sodium phosphate (GNAP) was developed. Germination of heat-activated spores in GNAP was equivalent to germination in FNA. Injury measured by colony formation on FNA and CNA was correlated to injury measured by reduced germination in both FNA and GNAP. Inactivation of the FNA and GNAP germination systems by secondary treatment exhibited similar kinetics. Therefore, injury expressed as the inability to form colonies on FNA involved alteration of the GNAP germination system.