The classical model of a murein monolayer for the structure of the murein sacculus of Escherichia coli is at present a controversial matter due to recent advances in the microscopic and biochemical knowledge of this cellular component (B. Glauner, J.-V. Höltje, and U. Schwarz, J. Biol. Chem. 263:10088-10095, 1988; M. Leduc, C. Frehel, E. Siegel, and J. van Heijenoort, manuscript in preparation). We have studied how the limitation in the supply of the murein-specific precursor meso-diaminopimelic acid (DAP) would affect cell growth and morphology as well as murein structure and content per unit of surface area in E. coli strains auxotrophic for DAP. Our observations indicated that the amount of murein per unit of cell surface area could be reduced by about 50% when the external concentration of DAP was equal to or lower than 0.5 microgram/ml. Cells with a reduced amount of murein did not show any detectable alteration in their morphology and characteristics of growth. Furthermore, no major alterations in murein structure were observed by high-pressure liquid chromatography analysis. However, the modification of murein that normally takes place at the initiation of the stationary phase was partially prevented. These results favor the alternative hypothesis of a thin, multilayered structure for the sacculus of E. coli rather than the monolayer model
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