[Effect of R plasmids on the DNA content of Escherichia coli].

The morphological properties, cell cycle and DNA content in rifampicin- and nalidixic acid-resistant mutants of E. coli M without plasmids and with R plasmids R6K and pKMR200 were studied. It was shown that the cells of the strains both containing the plasmids and containing no plasmids had elongated bacteria in their populations. Such bacteria were found to be nonseparated rods, 2-4 in number. The plasmids had an effect on the cell cycle period and DNA content: the presence of either R6K or pKMR200 induced lowering of the generation time and DNA content as compared to those in the strains without plasmids.