Mechanism of Defective Lysogenization by Phage P1 in a lon− Mutant of Escherichia coli K‐12

Phage P1 cannot lysogenize a lon– mutant of Escherichia coli K‐12, which is defective in the regulation of cellular division cycle to result in snake formation (14). P1 mutants, called P1pla, can lysogenize the lon– host. These mutations have been classified into two complementation groups: one is cis‐dominant; the other is trans‐dominant. A temperature‐sensitive lon– mutant was isolated, which exhibited the lon– phenotype at 42 C but not at 33 C. A temperature‐shift experiment of the P1‐lysogenic derivative of the lon– ts mutant showed lysis of the culture and induction of the phage production. It is proposed that P1 plasmid may be under a certain regulatory circuit of the division cycle of the host bacterium by indirectly regulating the production of P1 immune repressor, or alternatively by directly derepressing the functions of P1 prophage.