The behaviour of Rhizobium bacteriophages during and after exposure to ultraviolet radiation

SUMMARY: After inactivation by ultraviolet radiation, particles of two Rhizobium bacteriophages interfered temporarily with the multiplication of active particles of the homologous phage, in liquid cultures of their respective host bacteria. Inactivated particles did not affect the number of plaques produced by active particles in bacterial cultures on agar. No evidence was found that particles that were inactive singly became active when two or more of them infected the same bacterial cell. The rate of inactivation approximated closely to that of a first-order reaction. Exposing infected bacteria to visible light increased the residual activities of irradiated phage preparations by amounts equivalent to decreasing the doses of ultraviolet irradiation by a constant factor. Exposing either the irradiated phage preparations or the bacterial cultures separately to visible light had no effect. Those ultraviolet irradiated phage particles which remained active were so altered that they became relatively unstable