Bacterial Mutants Defective in Plasmid Formation: Requirement for the lon + Allele

Abstract

Bacterial mutants defective in plasmid formation were selected for their inability to be transduced to chloramphenicol resistance by bacteriophage PlCM. The mutants isolated are indistinguishable from a lon mutant strain. Both the lon strain and the mutants isolated here show very poor lysogenization by P1 and very low transduction to Gal⁺ by the plasmid formation of the λgal₈-Nam7am53cI₈₅₇. The lon⁺ gene function of the host bacteria is indispensable for plasmid formation, even though P1 and λ⁺ can grow normally on the lon strains and λ⁺ can be integrated normally in lon as well as in the lon⁺ bacteria. Phage mutants that can persist as plasmids in lon strains were isolated from P1CM. The function of the lon⁺ gene is discussed with regard to plasmid formation.