Changes in Ultraviolet Resistance and Photoproduct Formation as Early Events in Spore Germination of Bacillus Cereus T

In order to determine the timing of the change in the state of DNA in bacterial spores during the course of germination, L‐alanine‐induced germination of Bacillus cereus spores was interrupted by 0.3 M CaCl 2 as an inhibitor, and the resulting semi‐refractile spores (spores at the end of the first phase of germination) were examined on the UV‐resistance and the photoproduct formation. Upon UV‐irradiation, these spores, still having a semi‐refractile core as observed under a phase‐contrast microscope, gave rise to mainly the cyclobutane‐type thymine dimer. It was concluded that change in the state of the spore DNA occurs early in the process of germination, i.e. before the refractility of the core was lost. It was also found that CaCl 2 markedly prolonged the duration of the transient UV‐resistant stage.