THE EFFECT OF ULTRAVIOLET AND WHITE LIGHT ON GROWTH RATE, LYSIS, AND PHAGE PRODUCTION OF BACILLUS MEGATHERIUM

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Abstract
Cultures of B. megaterium 899a, growing under different conditions, were exposed to UV or white light. Cultures exposed to UV light and then to white light continue to grow at the normal rate. Cultures exposed to UV light and then placed in the dark grow at the normal rate for varying lengths of time, depending on conditions, and then lyse with the liberation of from 5 to 1000 phage particles per cell, depending on the culture medium. Increasing the time of exposure to UV light results in an increase in the fraction of cells which lyse in the dark. The lysis time decreases at first, remains constant over a wide range of exposure, and then increases. Lysis can be prevented by visible light after short exposure, but not after long exposures. The time required for lysis is independent of the cell concentration. After exposure to UV the cell concentration increases about 4 times at 20[degree], 30[degree], or 35[degree]C, but only 1.5 to 2.0 times at 40-45[degree]. This is due to the fact that the growth rate of the culture reaches a maximum at 38[degree] while the lysis rate increases steadily up to 45[degree]. Terramycin decreases the growth rate and lysis rate in proportion. After pH 5.1, the cultures continue to grow slowly in the dark after exposure to UV light. Sensitive cells infected with T-phage lyse more rapidly than UV-treated 899a; visible light does not affect the lysis time. The results agree with the assumption that exposure to UV results in the production of a toxic (mutagenic) substance inside the bacterial cell. This substance is inactivated by white light.