Gaseous environments modify reserve carbohydrate contents and cell survival in the brewing yeast Saccharomyces cerevisiae.

The use of H(2), He and O(2) during batch fermentation of Saccharomyces cerevisiae BRAS291 increased the final intracellular glycogen contents of the cells from 2-fold to 10-fold compared with a gas-free condition, and this depended on the gas applied. Differently, the intracellular trehalose contents increased from 2-fold to 10-fold in reducing conditions compared with more oxidizing conditions. During storage at 4 degrees C, the viability of cells cultivated with gas was twice that of cells cultivated without gas. These results could be explained by the intracellular carbohydrate contents as well as yeast ultrastructural modifications observed previously.

Metabolism of fatty acid in yeast: addition of reducing agents to the reaction medium influences beta-oxidation activities, gamma-decalactone production, and cell ultrastructure in Sporidiobolus ruinenii cultivated on ricinoleic acid methyl ester.

The sensitivity of Sporidiobolus ruinenii yeast to the use of reducing agents, reflected in changes in the oxidoreduction potential at pH 7 (Eh7) environment, ricinoleic acid methyl ester catabolism, gamma-decalactone synthesis, cofactor level, beta-oxidation activity, and ultrastructure of the cell, was studied. Three environmental conditions (corresponding to oxidative, neutral, and reducing conditions) were fixed with the use of air or air and reducing agents (hydrogen and dithiothreitol). Lowering Eh7 to neutral conditions (Eh7 = +30 mV and +2.5 mV) favoured the production of lactone more than the more oxidative condition (Eh7 = +350 mV). In contrast, when a reducing condition was used (Eh7 = -130 mV), the production of gamma-decalactone was very low. These results were linked to changes in the cofactor ratio during lactone production, to the beta-oxidation activity involved in decanolide synthesis, and to ultrastructural modification of the cell.

Metabolism of fatty acid in yeast: characterisation of beta-oxidation and ultrastructural changes in the genus Sporidiobolus sp. cultivated on ricinoleic acid methyl ester.

Cell structure modifications and beta-oxidation induction were monitored in two strains of Sporidiobolus, Sp. Ruinenii and Sp. pararoseus after cultivation on ricinoleic acid methyl ester. Ultrastructural observations of the yeast before and after cultivation on fatty acid esters did not reveal major modifications in Sp. ruinenii. Unexpectedly, in Sp. pararoseus a proliferation of the mitochondrion was observed. After induction, Sp. ruinenii principally exhibited an increase in the activities of acyl-CoA oxidase (ACO), hydroxyacyl-CoA deshydrogenase (HAD), thiolase and catalase. In contrast, Sp. pararoseus lacked ACO and catalase activities, but an increase in acyl-CoA deshydrogenase (ACDH) and enoyl-CoA hydratase (ECH) activity was observed. These data suggest that in Sp. ruinenii, beta-oxidation is preferentially localized in the microbody, whereas in Sp. pararoseus it might be localized in the mitochondria.