Bacterial mutants defective in plasmid formation: requirement for the lon + allele.

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 lambdagal(8)-Nam7am53cI(857). The lon(+) gene function of the host bacteria is indispensable for plasmid formation, even though P1 and lambda(+) can grow normally on the lon strains and lambda(+) 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.