MORPHOLOGICAL AND CHEMICAL PROPERTIES OF CELL ENVELOPES OF THE EXTREME HALOPHILE, HALOBACTERIUM CUTIRUBRUM

Abstract

In the electron microscope, isolated cell envelopes of the extremely halophilic bacterium, Halobacterium cutirubrum, have the same hexagonal surface pattern and roughly the same shape as do intact cells. At different pH values and in different ionic environments the envelopes undergo changes in shape and surface structure similar to those of intact cells. These changes are probably not due to osmotic pressure. In media of low ionic strength envelopes disintegrate. This disintegration appears to involve at least two reactions, both temperature-dependent.Chemical analyses show that envelopes consist mainly of lipoprotein. Both lipid and protein components are negatively charged at neutral pH, and this may help to explain the dependence on high cationic concentrations for envelope stability. Most of the cell"s phosphatides are present in the envelope. The main phosphorus-containing components of cells are acid-soluble compounds and nucleic acids, whereas the main phosphorus-containing components of envelopes are phosphatides. Envelopes also contain small amounts of hexoses, hexosamine(s), and nucleic acids with a higher RNA/DNA ratio than found in intact cells, but neither muramic acid nor diaminopimelic acid was present. The lack of muramic acid in H. cutirubrum indicates that this halophile does not have a rigid mucopeptide wall of the type found in other bacteria. The lack of mucopeptide in envelopes is not due to autolytic digestion of mucopeptide during envelope isolation.