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, Halobacteriunz 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 Dressure. In media of low ionic strennth envelooes disinte~rate. This disintegration appears to involve a t least tGo reaction's, both temperaturedependent.Chemical analyses show that envelopes consist mainly of lipoprotein. Both lipid and protein components are negatively charged a t neutral pH;and this may help t o explain the dependence on high cationic concentrations for envelope stabilitv. Most of the cell's ohos~hatides are oresent in the envelo~e. The main phosphbrus-containing compon&ts 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, b u t 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.

Membrane Biochemistry

“…These bacteria require high concentrations of salt (1 M to 4 M NaCI) prevent cell lysis, and evidence that the halophilic behavior may be related to an abnormality in membrane structure has emerged from the studies of Kushner, Brown, and 'their co-workers (34)(35)(36)(37), who showed that the requirement for high salt concentrations was also shown by isolated cell envelope preparations, which dissolved when placed in solutions of low ionic strength. These bacteria require high concentrations of salt (1 M to 4 M NaCI) prevent cell lysis, and evidence that the halophilic behavior may be related to an abnormality in membrane structure has emerged from the studies of Kushner, Brown, and 'their co-workers (34)(35)(36)(37), who showed that the requirement for high salt concentrations was also shown by isolated cell envelope preparations, which dissolved when placed in solutions of low ionic strength.…”

Structure of Biological Membranes

“…Gram-negative bacteria contain almost exclusively saturated and monounsaturated C16 and C18 fatty acids (59,60). Membranes of Halobacterium cutirubrum, a bacterium that grows only in solutions of sodium chloride that are at least 3M, dissolve in distilled water (67). Escherichia coli strain B may contain no unsaturated fatty acids (61).…”

Halobacterial glycoprotein biosynthesis

“…The cells lack the rigid murein sacculus and an outer membrane typical of Gram-negative eubacteria. Instead, halobacteria are surrounded by a single layer of hexagonally arranged protein subunits [7][8][9][10][11][12]. Xray diffraction studies as well as electron microscopy of thin sections were interpreted to demonstrate the existence of two protein layers outside the cytoplasmic membrane, separated by a 'periplasmatic space' [13,14].…”