Heat-stable and Density Mutants of Phages T1, T3 and T7

SUMMARY The coliphages T1, T3 and T7 rapidly lost infectivity when incubated at 60° in saline-citrate medium. From the survivors of heat-inactivated wild-type phage stocks heat-stable (st) mutants were isolated, which all had a reduced buoyant density. The st mutant phages of T3 and T7 contained 3 to 5% less DNA than their wild-type parent, while no loss of DNA could be detected for T1 st mutants. This correlation between heat stability and reduced density was confirmed by showing that a mutant of T3 selected for its lighter density had also mutated to heat-stability.