Abstract
The lethal effect of methylene blue (MB) plus light on extracellular phage T4o is mainly due to lesions in the DNA; the extent of this “DNA-specifity” is about 80% of that of the lethal effect of ultraviolet light. This has been concluded from marker rescue experiments performed with UV-as well as with photodynamically inactivated phages. The difference by a factor of 3.5 in the photodynamic sensitivity of T4o and T4o+ could be referred to the fact that the mutant lacks polyamines, because addition of spermine to T4o increases its resistance at least to the wildtype level. Glucose-containing and glucose-lacking T4-phages show almost the same photodynamic sensitivity so that the difference in the sensitivity of T4 and T2 probably is not due to their various degree of glucosylation.
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