Biomedical subjects
Publications and source records attributed to J Panos.
Ethanol tolerance of four Saccharomyces cerevisiae strains characterized by different amounts of delta 5,7-sterols was tested. The individual tolerances did not correlate with the strains sterol levels. The highly and medium-accumulating strains exhibited the highest and lowest ethanol tolerances, respectively.
delta 5,7-Sterol-accumulating Saccharomyces cerevisiae cells growing in chemostat at a specific growth rate of 0.075/h exhibited higher ethanol tolerance measured as ethanol-induced death and anaerobic growth inhibition than the cells growing at 0.2/h, the difference being dependent on the carbon-to-nitrogen molar proportion in the medium. The observed difference in sensitivity to ethanol of anaerobic growth between the slowly and rapidly-growing cells was completely reversed as a result of a block in sterol synthesis causing a negligible synthesis of delta 5,7-sterols. Two physiological parameters, budding frequency and membrane composition, evidently affected ethanol tolerance. Differences between the delta 5,7-sterol-synthesizing and deficient strains documented a profound effect of the quality of the sterol present on the physiological state of the cell.
Structural membrane lipids are known to contribute to the high ethanol resistance of Saccharomyces cerevisiae (2, 4, 17). By manipulating the yeast cellular sterol level by changing the carbon-to-nitrogen source ratio in the chemostat growth medium, high delta 5,7-sterol levels were found to increase the resistance of yeast populations to ethanol-induced death. The resistance of the erg2 (delta 8----delta 7-sterol isomerase) mutant to ethanol-induced death was generally comparable with that of the delta 5,7-sterol-synthesizing strain. In contrast, the sensitivity of anaerobic growth to inhibition by ethanol was higher in the erg2 mutant in comparison with the delta 5,7-sterol-synthesizing strains but a high level of those sterols increased the vulnerability of anaerobic growth to ethanol inhibition.
Phenylpropionic acid was determined in the fermentation medium by gas chromatography using an internal standard and by reversed phase high-performance liquid chromatography. The two methods were evaluated by using the standard quantitative criteria employed in analytical chemistry.
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Improved strain of Candida tropicalis 2838 grows on nonseparated straw hydrolyzates with no addition of vitamins and trace elements at a specific growth rate mu = 0.34 and 44% yield coefficient (referred to reducing substances). The reducing substances in hydrolyzates contain predominantly monosaccharides (xylose, glucose, arabinose, mannose). Cells grown in this way are rich in proteins (62%) and essential amino acids (lysine, phenylalanine, leucine, threonine and valine). The product obtained under industrial conditions by fermentation of the nonseparated hydrolyzates contains 8--9% of proteins and it is a suitable supplement of fodder mixtures for monogastric domestic animals. Nutrition tests on rats and pigs indicated that this product can substitute the hay-flour, and, partially, blood-flour barley, and that the strain used is nonpathogenic.
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