The Ultrastructure of the Cell Wall of Bacillus megaterium

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Abstract
The architecture of the cell wall of B. megaterium strain M was studied by using electron microscopy of shadowed or negatively stained preparations, ultrathin sections and simple chemical methods. No conspicuous visible structure was found on the surface of whole organisms, isolated cell walls or the "mucopeptide membranes". Hot formamide treatment decreased the thickness of cell walls by about 50%, leaving behind a rigid ?mucopeptide membrane''. The removed material is assumed to correspond with the "teichoic acid" bound presumably by chemical linkage to the rigid layer, thus forming a plastic layer of the cell wall. The total thickness of the cell wall ranged from 200 to 240 A, that of the rigid membranes from 90 to 110 A. Poststaining of glutaraldehyde-fixed organisms or cell walls with osmium tetroxide, potassium permanganate or lead citrate produced a "triple layered" cell-wall profile. This was not the case with uranyl acetate or phosphomolybdate staining, where the cell wall was represented by one homogeneous and dense track.