[Temperature-dependent mutants of Hly plasmid and their use for the purpose of confirming the cytotoxic activity of E. coli hemolysin].

Two different mutants of Hly 212 plasmide induced by diethyl sulfate were isolated; one of these was characterized by temperature-dependent synthesis, and the other--by temperature-sensitivity of hemolysin produced. In difference from bacteria possessing wild parental plasmide, E. coli K12 bacteria which contained the mutants produced no cytotoxic action on the MK2 cell culture. This correlated with the absence of the hemolytic activity in growing them even at permissible temperature on medium No 199. After crossing the mutant plasmides there were obtained clones with completely restored wild phenotype of the hemolysin production and the cytotoxic activity. The data obtained pointed to the relationship between the cytotoxicity and hemolysin.