A permeability mutant of Yersinia pestis with increased susceptibility to phagocytosis which retains potential for intraphagocytic growth and virulence.

Gentian violet resistance was used to select mutants of Yersinia pestis with altered cell envelope permeability. Mutants in one class lacked the 6 and 61 megadalton (Mdal) plasmids, but retained the 47 Mdal plasmid associated with calcium dependence. Mutants in a second class retained all three plasmids. One mutant in the latter class, EV76S7, lacked major outer membrane protein J and yielded reduced levels of minor outer membrane proteins A and C. Protein J is known to interact differently with lipopolysaccharide (LPS) from cells bearing and cells lacking the 47 Mdal plasmid following growth at 37 degrees C. The 47 Mdal plasmid is known to influence gentian violet uptake, novobiocin sensitivity, susceptibility to phagocytosis, the growth in macrophages and the virulence of Y. pestis. Gentian violet uptake was lower and novobiocin sensitivity higher in the mutant than in the parental strain, but the underlying effects of the 47 Mdal plasmid on these parameters had not changed. EV76S7 cells were phagocytized to a greater extent than the parental cells following growth at 37 degrees C, but survival and growth within peritoneal phagocytes and the LD50's of cells with and without the 47 Mdal plasmid were not altered by the loss of protein J, we conclude that protein J--LPS interactions are not required for virulence, and that the reduced virulence of cells lacking the 47 Mdal plasmid does not result from the altered protein J--LPS interactions which are known to result from loss of the plasmid.