Integration of Chloramphenicol Resistance Gene of an R Factor on Escherichia coli Chromosome

An unstable mutant R factor conferring only chloramphenicol (CM) resistance was obtained by spontaneous segregation. After storage in broth culture, a stable CM‐resistant mutant was obtained and its CM‐resistance could not be cured by treatment with acriflavine or transduced to a recombination‐deficient strain of Escherichia coli K12. Recombinational analysis indicated that the cml gene governing CM resistance had been integrated into the E. coli chromosome and closely linked with met B locus. The cml gene was co‐transduced with both met and arg markers by phage P1, and the linkage order was considered to be mtl‐cml‐met‐arg‐thi. When the strain carrying this chromosomal CM‐resistance was infected with a transferable R (TC) factor capable of conferring tetracycline (TC) resistance, the CM‐resistance became transferable by conjugation. This mechanism is considered to account for the formation of the recombinant R (TC.CM) factor.