Abstract
Seven temperate coliphages recovered from naturally occurring lysogenic strains of Escherichia coli were found to lyse E. coli C but not K12. Four of these C-specific phages produced mutants (hrk) able to grow on K cells. The K cells harbouring HK253hrk and HK183hrk were converted so that they could adsorb and be lysed by three other nonmutant C-specific phages. HK253, HK183 and two other phages were shown to recombine with phage lambda.