Investigation of osmotically stable spheroplasts from two strains of Escherichia coli ML-35, W7-M5.

Osmotically stable spheroplasts were produced from Escherichia coli ML-35 and W7-M5 using either 1 min exposure to polymyxin B or 10 min exposure to Tris/EDTA, followed by 1 to 3 h incubation with lysozyme. Spheroplast membrane permeability studies were conducted using paired radioactive probes with E. coli ML-35. Experiments with 14C-sucrose-16 kD 3H-dextran indicated that the outer membrane had lost its barrier to 16 kD dextran. Parallel experiments with 81 kD 3H-dextran indicated that the outer membrane was impermeable to the larger dextran. EDTA treated cells also showed outer membrane permeability to 16 kD dextran. Cytoplasmic membrane integrity was confirmed using 14C-sucrose and 3H2O before and after exposure to polymyxin B and EDTA. Scanning electron microscopy showed that a rough surface on polymyxin B produced spheroplasts while Tris/EDTA spheroplasts showed the same smooth surface as control cells.