HETEROGENEITY OF YERSINIA-PSEUDOTUBERCULOSIS COLLECTION STRAINS AND THEIR MOLECULAR AND BIOLOGICAL PROPERTIES

The capacity of Y. pseudotuberculosis strains for disassociation with the appearance of S- and P-forms has been studied. Strains 852 and 9547 show high stability in S-forms, their conversion into R-forms occurring at 40-42-degrees-C. Strain 6953 shows pronounced polymorphism and instability of its associations at different growth temperatures. Strain 9532 exists in S- and R-forms which retain their stability during numerous subculturings at different growth temperatures and prolonged storage. This strain has plasmids of 130, 72.2, 5.7 kb. All plasmids are retained in S- and R-forms, i.e. the dissociation of the strain is not accompanied by the loss of plasmids. The conversion of the strain from the S-form into the R-form leads to changes in the structure of lipopolysaccharide and the composition of low-molecular (less than 23 kD) proteins in the outer and inner membranes. In tests on guinea pigs the LD50 of the R-form of the strain is tenfold greater than that of its S-form. The dissociants of strain 9532 are transformed by plasmid DNA with equal efficiency and equally inherit them without selective pressure.