Visualization of thermal inactivation in phages lambda and φ80

Abstract

Using electron microscopy, it has been shown that DNA is released from λ phage particles by heat treatment in the presence of EDTA. The destruction of phage particles, which may cause the release of phage DNA during preparation, was minimized by preventing the specimen from drying up. Under our conditions, the percentage of complete phage particles in the unheated λb2 +cI preparation was more than 90%. The particle heads of λb2 +cI and wild type φ80 were ruptured by heat treatment, and the DNA-like threads were released. These threads were identified as DNA from their sensitivity to DNase I. The frequencies of full-head particles observed after heat treatment were related to the number of survivors expected. Thus, the main lethal event during heat inactivation is attributed to the release of DNA from phage particles which results in destruction of the structure of the head coat.