[Various properties of RifR mutants of the plague agent]

The properties of the RifR mutants of four vaccinal and two natural strains of the plague bacillus were studied. The frequency of the mutants not growing on the complete nutrient medium after increasing the cultivation temperature to 37 degrees C averaged to 3.10(-1). The frequency of the loss of every of the three known autonomous plasmids or combinations of the 6-mD and 65-mD plasmids was n.10(-1). In the mutants of some strains with the preserved 47-mD plasmid sensitivity to the Ca2+ deficiency markedly lowered (but was not lost). The mutants of the majority of the strains produced much lower quantities of bacteriocin (pesticin I). The nutritional requirements, enzymatic activity, sensitivity to the diagnostic phage and the level of the production of fraction I, a specific antigen, in the bacillus did not change.