ESR Studies on the Membrane Properties of a Moderately Halophilic Bacterium

Abstract

The lipid membrane properties of a moderately halophilic gram-negative bacterium, Pseudomonas halosaccharolytica ATCC 29423, were studied by the use of stearate spin labels, 5NS, 12NS, and 16NS, changing the temperature of ESR measurement from 15 to 50 degrees C. The order parameter and the rotational correlation time of the spin labels incorporated into intact cell membranes of this bacterium grown at various temperatures in media containing different NaCl concentrations were calculated. The activation energy of rotational microviscosity was obtained from Andrade plots. At low growth temperature and low NaCl concentration in the medium, extractable lipids of this bacterium contained comparatively large amounts of unsaturated fatty acids, but as the growth temperature and NaCl concentration in the medium increased, the contents of saturated and cyclopropanoic fatty acids increased to more than half of the total fatty acids. 5NS gave the highest order parameters for the intact cells of this bacterium, while 12NS gave lower and 16NS gave the lowest results. The order parameters of 5NS, 12NS, and 16NS were completely separated, and all order parameters decreased gradually as the measuring temperature was increased. In contrast, the rotational correlation times of the intact cells with 12NS were as large as those with 5NS, while those with 16NS were distinctly smaller. Increasing NaCl concentrations in the growth medium caused an increase of the rotational correlation times, that is, stiffened the lipid bilayers. The Andrade plot for 16NS was approximately a straight line, whereas 5NS and 12NS gave two straight lines crossing at a temperature near the growth temperature, indicating phase transition from solid to liquid. The microviscosity activation energies were 5--10 kcal/mol in the liquid phase and 15--25 kcal/mol in the solid phase.

Biology of Moderately Halophilic Aerobic Bacteria

“…All calculations are based on the (not necessarily true) assumption that the molecules used as markers are not taken up and metabolized by the cells or bound to the envelopes and other cellular structures. Indeed, it was suggested that dextran and inulin may bind to cell envelopes (130) and that smaller fragments of unpurified dextran may be taken up by the cells, causing large errors in the calculation of the cytoplasmic solute concentrations. That a proper knowledge of the intracellular water space under different growth conditions is essential and that a comparative approach based, e.g., on the ion content per unit of cell protein is insufficient is clearly shown by the finding that in H. elongata the cell volume per unit of protein is inversely related to salinity, decreasing from 2.62 to 2.06 l/mg of protein in cells grown from 0.175 to 1.37 M NaCl (203).…”

Halophilic Microorganisms and their Environments

“…The cyclopropane fatty acid synthetase is either an integral membrane protein or is associated with the membrane. Its activity is inhibited by NaCl or KCl, but stimulated up to 12-fold by 3 M glycine betaine Hyono et al, 1979Hyono et al, , 1980Kuriyama et al, 1982;Monteoliva-Sanchez et al, 1993;Ohno et al, 1976Ohno et al, , 1979. Electron paramagnetic resonance studies of rotational movements of lipids in the membranes in intact "Pseudomonas halosaccharolytica" cells showed the presence of an unusually thick (up to a depth of 12 carbons from the hydrophobic surface) viscous surface region in the membrane bilayer.…”

“…of the micro-viscosity of the polar surface in the lipid bilayer. The presence of thick viscous regions may be related to the need to withstand high osmotic pressure or to the requirement for a low permeability to Hyono et al, 1979Hyono et al, , 1980Kuriyama et al, 1982).…”

In Vitro Effects of Colchicine on Human Erythrocyte Membranes: An ESR Study

“…Eqn. (2) is suitable for a rod-like molecule and especially for perpendicular resonance spectra (Hyono et al, 1980). Because of assumptions made in the derivation of Eqn.…”

“…For a rod-like molecule of radius, r, and length, /, the rotational correlation time is related to the rotational viscosity as (Hyono et al, 1980):…”