Excretion of glutamic acid in Citrobacter intermedius C3 associated with plasmid deoxyribonucleic acid

Several mutants of Citrobacter intermedius C3 lacking both the ability to synthesize proline and the ability to excrete glutamic acid were isolated by treatment with nitrosoguanidine. No revertants for either characteristic were obtained from these mutants. The ability to excrete glutamic acid was transferred to those mutants with very high frequencies in mating experience by using auxotropic excreting strains as donors. Moreover, the ability to synthesize proline was transferred together with the ability to excrete glutamic acid when an excreting strain was used as donor. The transconjugants showed a rapid spontaneous curing of both genetic markers. It was shown by two different methods that a band of covalently closed circular deoxyribonucleic acid is present in the cesium chloride gradients corresponding to the wild type and excretor mutants. Nonexcretor mutants described herein lacked such a band. Pro + transformants that were also excretors were obtained with plasmid deoxyribonucleic acid isolated either from wild type or from an excretor mutant. These data strongly indicate that glutamic acid excretion in C. intermedius C3 is related to the presence of extrachromosomal deoxyribonucleic acid.