The effect of osmotic shock on the accessibility of the murein layer of exponentially growing Escherichia coli to lysozyme.

The restricted access of lysozyme to the murein layer of exponential phase Escherichia coli is enhanced considerably by osmotic shock. When cells suspended in Tris/EDTA/sucrose are diluted 11-fold in water or 10 mM EDTA in the presence of lysozyme, their susceptibility to lysozyme increases by a factor of 50--100, for both Escherichia coli JC411 and W3110, grown to the early exponential phase in unsuppleneted or supplemented minimal media, and in Brain Heart Infusion. Since an 11-fold dilution causes lysis of lysozyme spheroplasts, the effects of a 2-fold dilution have also been investigated. A 2-fold dilution of cell suspended in TrisEDTA/sucrose still increases their susceptibility to lysozyme by a factor of 10--50, but the resulting spheroplasts remain intact. EDTA is necessary to permit lysozyme access to the murein layer during the dilution, which is ineffective in the presence of 5 mM MgCl2. These results are discussed in terms of the formation of lysozyme spheroplasts from young Escherichia coli.