Abstract
Abstract : Experiments were designed to define phenomena of virulence antigen production, bacterial stasis, and lysis in virulent Pasteurella pestis. The observations, by Lawton, that Mg ''induces'' and Ca ''represses'' virulence antigduc tion were verified. Optimal production of these antigens occurred in a chemically defined medium containing 0.02 M MgCl2. and no added CaCl2. This environment results in stasis of cells possessing the genetic potential for producing virulence antigens. The addition of 0.0025 M Ca in the presence of 0. 02 M Mg completely repressed the production of these antigens and permitted cell division to occur. Cells of the rare avirulent mutant type that produces virulence antigens and forms a typical colonies on agar made Ca-deficient grow more slowly in Ca-deficient broth than do those avirulent cells that produce no virulence antigens. Of 16 tested energy sources, none was found to enhance virulence antigen production in the presence of Mg without equally favoring cell division in the presence of Ca. Induced virulent cells retained their morphological integrity; however, they appeared to be somewhat larger and the formation of new cross-septa was not observed.
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