Effects of wash treatments on the ultrastructure and lysozyme penetrability of the outer membrane of various marine and two terrestrial gram-negative bacteria

Twenty-three marine and two terrestrial gram-negative bacteria were examined for the effect on the outer membrane of the cells of washing the organisms successively in 0.5 M NaCl and 0.5 M sucrose, a procedure which brings about the loss of the outer membrane from Alteromonas haloplanktis 214. Six organisms lost their outer membrane completely, three lost it partially, and six retained it but in a form which indicated that the membrane had been affected extensively. The remaining 10 organisms including the two terrestrial species, Escherichia coli and Pseudomonas aeruginosa, showed no changes detectable in thin section by electron microscopy. None of the 16 organisms which retained their outer membrane after washing were converted from rod forms to spheres by lysozyme before washing but 12, including Pseudomonas aeruginosa, formed spheres in the presence of the enzyme after the wash treatment. For many of the latter organisms, treatment with lysozyme caused large segments of the outer membrane of the cells to be removed. Losses in cell viability following washing and treatment with lysozyme paralleled the extent of damage to the outer membrane perceived by electron microscopy.