The Location of the Mucopeptide in Sections of the Cell Wall of Escherichia Coli and Other Gram-Negative Bacteria

Electron micrographs of sections of Escherichia coli have shown that the wall has an extra component 20–30 Å in thickness on the inside of the usual double-track profile. Demonstration was aided by treating the sections with uranium, lanthanum, thallium, or lead salts. This innermost layer alone was lost in spheroplasts produced by penicillin poisoning or treatment with lysozyme-EDTA, and was removed from isolated cell walls by lysozyme. The innermost layer is considered, therefore, to contain the mucopeptide characteristic of bacteria. The inner taut layer (or "intermediate layer") of Spirillum serpens, Vitreoscilla sp., and Simonsiella sp. was also found to be lysozyme sensitive. In the latter species this layer was the sole component of the septum, so that the outer cell wall components enclosed the elements of the trichoma. Other components were less easily localized but it was considered that the lipoprotein layer was outside of the limits of the wall profile usually visualized in sections. The outer layers generally loosened during embedding, but in E. coli and some others the layers all stayed tightly adherent to each other. The Gram-negative bacteria seem to have the double-track layer and the mucopeptide as a basic complement for the cell wall.