Nucleic acid synthesis in ultraviolet-irradiated Bacillus cereus.

Kelner (J. Bacteriol., 65, 252, 1953), has found that ultraviolet irradiation inhibits deoxyribonucleic acid synthesis in Escherichia coli strain B/r. He sometimes observed a resumption of this synthesis after a certain period of postirradiation incubation. This has also been reported by Kanazir and Errera (Cold Spring Harbor Symposia Quant. Biol., 21, 19, 1956). As most of the irradiated cells were inactivated one wonders whether the deoxyribonucleic acid synthesized after the cells were exposed to ultraviolet irradiation was normally functioning nucleic acid. Not all bacteria seem to behave like E. coli. Bacillus cereus strain p2 was grown at 37 C in brain heart infusion broth (Difco) which was supplemented with 1 per cent of glucose and 0.5 per cent of phosphate. The pH was kept at 7.2 by adding potassium hydroxide. The culture was vigorously stirred during the whole experiment. At a certain cell density the cells were exposed to ultraviolet irradiation. The dose rate was about 600,uwatt per cm2. After the irradiation, the cells were incubated for one generation time (50 to 60 min) and harvested. There was no noticeable inhibition of over-all growth of the culture (turbidity), growvth of the survivors (number of viable cells), or ribonucleic and deoxyribonucleic acid synthesis during this period. This is shown in tables 1 to 3. To test the hypothesis that the postirradiation-formed nucleic acids