Influence of osmotic pressure on transformable and non transformable variants of Neisseria meningitidis. 3. Fragility of the cell membranes.

Penicillin spheroplasts from competent (cp+) and incompetent (cp-) variants of Neisseria meningitidis Strain M1 were equally fragile as determined by the osmotic strength necessary for stabilization. Exponential phase cells adapted to growth under increased osmotic pressure and suspended in acetate or phosphate became osmotically fragile within 2-4 hour when stabilized by sucrose plus MgCl2. Spheroplasts were formed during the succeeding 6-12 hours. Cells that were not adapted to growth at high tonicity but exposed to the stabilizing fluid under conditions leading to plasmolysis, developed osmotic fragility more rapidly, but at the same time lysis of the membranes was activated. Under these conditions, membrane lysis occurred far more rapidly in the cp-variant than in the cp+ variant. Membrane lysis was inhibited by MgCl2 and enhanced by CaCl2 in low concentration. The findings support the notion that osmotic stress in N. meningitidis activates membrane lysis as well as cell wall lysis, and that both activations are far more pronounced in the cp- variant. But the relative protection of the cp+ variant cannot be due to higher tensile strength of the membranes.