Publisher Summary This chapter reviews the effects of alcohols on microorganisms. Alcohols are ubiquitous small molecules, which are produced both chemically and as products of microbial fermentation. Accumulation of alcohols in the microbial environment represents a form of environmental stress, analogous to extremes in pH value and temperature. The chapter discusses the action of ethanol and other alcohols on microorganisms, explains several important mechanisms of action. Alcohols have been employed for many years both as a disinfectant and as a preservative. Concentrations of ethanol above 15% result in immediate inactivation of most vegetative organisms, with spores being considerably more resistant. Low concentrations of ethanol also render bacteria more sensitive to inactivation by ionizing radiation and by lipophilic acids. The chapter concludes that the basic actions of alcohols on both eukaryotic and prokaryotic organisms share the same general principles. These effects appear to be dominated by the physicochemical properties of alcohols rather than involving specific receptors. All hydrophobic and electrostatic interactions in the cytosolic and envelope components of cells can potentially be affected. These include membranes, conformations of enzymes and macromolecules, activity coefficients of metabolites, permitivity, ionization potentials, pK values of functional groups, and pH value.

Effects of Alcohols on Micro-Organisms

Lipid domains in membranes. Evidence derived from structural perturbations induced by free fatty acids and lifetime heterogeneity analysis.

1-[4-(Trimethylamino)phenyl]-6-phenylhexa-1,3,5-triene (TMA-DPH), a cationic analogue of diphenylhexatriene (DPH), has photophysical properties that are generally similar to those of DPH. In solution the fluorescence lifetime (tau) of TMA-DPH is short (less than 1.5 ns), but tau increases to approximately 7 ns when the probe is embedded in lipid bilayers at temperatures less than the thermal transition temperature (Tc) of the lipid. The cationic charge ensures that the probe is anchored at the lipid-water interface, most likely with the DPH moiety intercalated between the upper portions of the fatty acyl chains. The profiles of changes in steady-state anisotropies (rss) and limiting hindered anisotropies (r infinity) are similar for both TMA-DPH and DPH embedded in lipid bilayers, but r infinity values for TMA-DPH even at T much greater than Tc are generally greater than 0.14, e.g., at 35 degrees C in 1,2-dimyristoylglycero-3-phosphocholine (DMPC) (cf. 0.03 for DPH in DMPC at 35 degrees C). Electrostatic interactions of the cationic probe with head groups of phospholipids do not appear to significantly influence the apparent dynamics of the probe. TMA-DPH should prove useful in the study of the dynamics of phospholipid monolayers, e.g., in native or reconstituted lipoproteins.

1-[4-(Trimethylamino)phenyl]-6-phenylhexa-1,3,5-triene: synthesis, fluorescence properties, and use as a fluorescence probe of lipid bilayers.

The effects of ethanol on the fluidity of Escherichia coli plasma membranes were examined by using a variety of fluorescent probes: 1,6-diphenyl-1,3,5-hexatriene, perylene, and a set of n-(9-anthroyloxy) fatty acids. The anthroyloxy fatty acid probes were used to examine the fluidity gradient across the width of the plasma membrane and artificial membranes prepared from lipid extracts of plasma membranes. Ethanol caused a small decrease in the polarization of probes primarily located near the membrane surface. In comparison, hexanol decreased the polarization of probes located more deeply in the membrane. Temperature had a large effect on probes located at all depths. The effects of ethanol on E. coli membranes from cells grown with or without ethanol were also examined. Plasma membranes isolated from cells grown in the presence of ethanol were more rigid than those from control cells. In contrast to plasma membranes, artificial membranes prepared from lipid extracts of ethanol-grown cells were more fluid than those from control cells. These differences are explained by analyses of membrane composition. Membranes from cells grown in the presence of ethanol are more rigid than those from control cells due to a decrease in the lipid-to-protein ratio. This change more than compensates for the fluidizing effect of ethanol and the ethanol-induced increase in membrane C18:1 fatty acid which occurs during growth. Our results suggest that the regulation of the lipid-to-protein ratio of the plasma membrane may be an important adaptive response of E. coli to growth in the presence of ethanol.

Effects of ethanol on the Escherichia coli plasma membrane.

Amyloid beta-protein interactions with membranes and cholesterol: causes or casualties of Alzheimer's disease.

Pulse Fourier transform proton magnetic resonance techniques have been used to determine (i) the precise location of four membrane fluorescent probe molecules in lipid bilayer model membranes above the gel-to-liquid crystal transition temperature, tm; (ii) the dynamical perturbation of the host lipid molecules induced by incorporation of the probe into the bilayer. The regions of maximal perturbation induced by these probes do not necessarily coincide with their actual location in the bilayer.

J K Blasie

Papers

Nuclear magnetic resonance studies of lecithin bimolecular leaflets with incorporated fluorescent probes.