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The Effects of Ultraviolet Irradiation on Mycobacteriophages and their Infectious DNAs

Department of Medical Microbiology and Immunology, School of Medicine, University of California, Los Angeles, California 90024

Mycobacteriophages D4, D29, D29A and D32, their isolated DNAs and their host, Mycobacterium smegmatis, ATCC 607, are highly resistant to u.v. irradiation. Infective DNA appeared more resistant than intact phage but this difference was in part due to shielding by the greater u.v. absorbency of the DNA solutions. It was, however, also due to the occurrence of non-reversible u.v. damage to phage protein. D29, D29A and D32 and their DNAs showed two-component dose-survival curves, D4 and its DNA were inactivated exponentially, while M. smegmatis showed a non-linear semilog curve with a distinct shoulder in the low-dose region. M. smegmatis possesses a mechanism for reversing u.v. damage to the bacterial genome and to the genome of infecting phage by photoreactivation. Specific dark-repair mechanisms were not identified, except in the case of a significant level of acriflavin-sensitive host-cell reactivation demonstrated for D29. The observed enhancement of survival of heavily irradiated D29 and D4 by pretreatment of the assay bacteria with iodoacetate was interpreted as evidence that a delay of growth and division of the host, and/or a delay of phage replication, contributed indirectly to a dark-repair mechanism.

^* Fulbright Postdoctoral Scholar. Present address: Department of Tuberculosis, National Institute of Health, Tokyo, Japan.

Received 7 July 1969; accepted 6 February 1970.