Electrochemical and Mechanical Interactions in Bacillus Spore and Vegetative Mureins

摘要

The murein serves as a unimolecular, protective envelope around the protoplast of a bacterial cell and is important in osmotic resistance, ion exchange, antigenicity, toxigenicity, and in the molecular sieving which determines the osmotrophic feeding habits of bacteria. The mechanical functions of mureins seem to be archetypical, especially for gram-positive bacteria. These organisms have a thick, elastic, murein shell and a turgidity associated with internal osmotic pressures as great as 30 atmospheres (3.0 MPa). In the turgrid cell, the murein is stretched and under tension. Plasmolysis of the cell results in shrinking not only of the protoplast but also the whole cell. Koch et al. have recently proposed roles for murein tension and cell turgor in bacterial wall growth. Mechanical functions of mureins important for vegetative cells appear to be accentuated in endospores. These biologically extreme cells consist of a central, relatively dehydrated core or protoplast, a thin envelope of vegetative murein, a thick cortex of spore murein, and outer inverted membrane, protein coat layers, and in many spores, and external, loosely fitting, chemically complex exosporium. Insoluble mureins of B. megaterium spores appear to be highly elastic, flexible and well designed for their roles in containing the highly hydrostatic pressures of the spore core. The electrochemical properties of spore mureins can be predicted at least roughly from a knowledge of their chemical structure and the known behavior of vegetative mureins.