Characterization of a stable spheroplast type L-form of Proteus mirabilis D 52 as cell envelope mutant. II. Electronmicroscopic investigations.

The ultrastructural analysis of a stable spheroplast type L-form of Proteus mirabilis D 52 revealed characteristic alterations in the organization of the cell envelope including defective changes in the cell envelope structure as for instance the loss of a coherent murein layer, the loss of some components in the outer cell wall layer, the formation of small membraneous vesicles at the tips of loose extensions of the cell wall, a decrease in associations and bindings between wall and membrane, an extension of the periplasmic space, an increase in membrane defects, as well as a disturbed cell division causing unusual modes of multiplication and the formation of various intracellular structures like membrane complexes, characteristic sheet-like membraneous bodies, typical inclusion bodies, and defective phage structures, which all could not be observed in normal rod-shaped cells. The results of these investigations and of those given in a previous paper (Gumpert and Taubeneck 1975) show, that the stable spheroplast type L-form LD 52 B must be considered as a true cell envelope mutant in which the biosynthesis and structure of the cell envelope is altered genetically by one or several mutations whereas the main biochemical activities are the same like those of the parent bacterium. The profound alterations in the cell envelope system, however, lead to some changes in the whole cell organization, which apparently in turn cause disorders even in metabolic and biosynthetic processes not directly involved in the biosynthesis of the cell envelope.