Sterols are vital components of all eukaryotic cells. This review describes the variety of sterol structures found in microalgae, yeasts, fungi, protozoans and microheterotrophs. Reports of the occurrence of sterols in prokaryotic cells are critically assessed. Methylotrophic bacteria contain unusual 4-methylsterols, but reports of 4-desmethyl sterols in cyanobacteria and other bacteria are limited and many of these seem dubious. Possible application areas for sterols derived from mass culture of microalgae and other microorganisms are highlighted.

Sterols in microorganisms.

(1983). Sterol, Structure and Membrane Function. Critical Reviews in Biochemistry: Vol. 14, No. 1, pp. 47-92.

Sterol structure and membrane function.

Lipids and membrane function in green algae

Although traditionally used as a valuable health supporting nutrient, the vegetative parts of Opuntia spp. plants are scarcely used in modern nutrition and medicine. While all kinds of different Opuntia spp. have been studied, a systematic approach regarding the inter-relationships between the composition and the pre- and postharvest conditions is still missing. Therefore, the present review compiles and discusses literature on the chemical composition of cactus stems, the knowledge on uses in food, medicine, and cosmetics. It is concluded that much research is needed to get an insight into the multitude of bioactivities reported in the traditional literature but also to take advantage of the respective constituents for food and pharmaceutical applications.

Cactus stems (Opuntia spp.): A review on their chemistry, technology, and uses

It is now certain that the inherent ethanol tolerance of the Saccharomyces strain used is not the prime factor regulating the level of ethanol that can be produced in a high sugar brewing, wine, sake, or distillery fermentation. In fact, in terms of the maximum concentration that these yeasts can produce under batch (16 to 17% [v/v]) or fed-batch conditions, there is clearly no difference in ethanol tolerance. This is not to say, however, that under defined conditions there is no difference in ethanol tolerance among different Saccharomyces yeasts. This property, although a genetic determinant, is clearly influenced by many factors (carbohydrate level, wort nutrition, temperature, osmotic pressure/water activity, and substrate concentration), and each yeast strain reacts to each factor differently. This will indeed lead to differences in measured tolerance. Thus, it is extremely important that each of these be taken into consideration when determining "tolerance" for a particular set of fermentation conditions. The manner in which each alcohol-related industry has evolved is now known to have played a major role in determining traditional thinking on ethanol tolerance in Saccharomyces yeasts. It is interesting to speculate on how different our thinking on ethanol tolerance would be today if sake fermentations had not evolved with successive mashing and simultaneous saccharification and fermentation of rice carbohydrate, if distillers' worts were clarified prior to fermentation but brewers' wort were not, and if grape skins with their associated unsaturated lipids had not been an integral part of red wine musts. The time is now ripe for ethanol-related industries to take advantage of these findings to improve the economies of production. In the authors' opinion, breweries could produce higher alcohol beers if oxygenation (leading to unsaturated lipids) and "usable" nitrogen source levels were increased in high gravity worts. White wine fermentations could also, if desired, match the higher ethanol levels in red wines if oxygenation (to provide the unsaturated lipids deleted in part by the removal of the grape skins) were practiced and if care were given to assimilable nitrogen concentrations. This would hold true even at 10 to 14 degrees C, and the more rapid fermentations would maximize utilization of winery tankage.(ABSTRACT TRUNCATED AT 400 WORDS)

Ethanol Tolerance in Yeasts

http://www.jbc.org/content/253/17/6218.full.pdf

The functional importance of structural features of ergosterol in yeast.

Dominance of Δ5-sterols in eight species of the cactaceae

Purified flagella of the eukaryotic algaChlamydomonas reinhardi have a sterol composition (55% ergosterol [24β-methylcholesta-5,7,22-trans-trien-3β-ol] and 45% 7-dehydroporiferasterol [24β-ethylcholesta-5,7,22-trans-trien-3β-ol]) identical of that of the whole algal cell. Fatty acids isolated fromC. reinhardi flagella were identified as 16∶0, 18∶0, 18∶1, 18∶2 and 18∶3. Whole cell fatty acids included 14∶0, 16∶2 and 16∶3 in addition to those found in the flagella. Triunsaturates comprised 22.9% of the flagellar fatty acids and 76.4% of those from the whole cell.

The sterols and fatty acids from purified flagella ofChlamydomonas reinhardi

Samples of ergosterol isolated fromSaccharomyces cerevisiae, Neurospora crassa, andAgaricus sp., and commercial ergosterol all displayed identical proton magnetic resonance (PMR) spectra at 220 MHz. From the effects produced on the doublet for C-21 by epimerization at C-20 and C-24 in sterols of known configuration, the absolute configurations at these positions in ergosterol were determined. The data demonstrate that ergosterol from both Ascomycetes and Basidiomycetes is the same and that at C-20 and C-24, the two H-atoms are on the α-side of the asymmetric carbon atoms and that C-22 istrans-oriented with respect to C-13 about the 17(20)-bond.

Determination of the absolute configuration at C-20 and C-24 of ergosterol in Ascomycetes and Basidiomycetes by proton magnetic resonance spectroscopy.

The 4-desmethylsterols from the leaves ofBeta vulgaris are a mixture of Δ(7)-sterols (71%) and Δ(5)-sterols (29%). The Δ(7)-sterols isolated are spinasterol (24α-ethylcholesta-7,22-dien-3β-ol; 45%), 22-dihydrospinasterol (24α-ethylcholest-7-en-3β-ol; 24%), and avenasterol (24-ethylcholesta-7,24(28)-dien-3β-ol; 1.5%). The Δ(5)-sterols isolated are sitosterol (24α-ethylcholest-5-en-3β-ol; 15%), 24ζ-ethylcholesta-5,22-dien-3β-ol (7.5%), and 24ζ-methylcholest-5-en-3β-ol (7%).

John H. Adler

Papers

The functional importance of structural features of ergosterol in yeast.

Dominance of Δ5-sterols in eight species of the cactaceae

The sterols and fatty acids from purified flagella ofChlamydomonas reinhardi

Determination of the absolute configuration at C-20 and C-24 of ergosterol in Ascomycetes and Basidiomycetes by proton magnetic resonance spectroscopy.

Cooccurrence of C-24 alkylated Δ7- and Δ5-Sterols in the leaves ofBeta vulgarisin the leaves ofBeta vulgaris