Metabolism of fatty acid in yeast: addition of reducing agents to the reaction medium influences β-oxidation activities, γ-decalactone production, and cell ultrastructure inSporidiobolus ruineniicultivated on ricinoleic acid methyl ester

Abstract

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.

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

“…Similarly, during chronological aging of S. cerevisiae culture, the survival was directly correlated to the decrease of glycogen and trehalose contents of yeast (Samokhvalov et al 2004). Moreover, previous observations showed modifications of yeast cell size, morphology and ultra-structure in gaseous environments (Feron et al 2007;Pham et al 2007a). In particular modifications of the cell wall were observed.…”

“…It was not the case for the trehalose content which was influenced mainly by the redox environment. A modification of external redox potential can affect the physiology of microorganism by altering membrane structure and properties (permeability, potential) (Riondet et al 1999;Kirakosyan et al 2004) as well as the internal redox state (Feron et al 2007;Pham et al 2007b). Thus, in our case, it seems likely that gas-in culture conditions, especially with O 2 and H 2 , correspond to conditions of stress for yeast cells, leading to accumulation of storage substances.…”

“…Among the different environmental parameters (pH, temperature, osmotic pressure etc.) able to modify the environment of the cell, the oxidoreduction potential (Eh) influences yeast cell physiology at different levels, i.e., growth as well as metabolism (Cachon et al 2002;Husson et al 2006;Feron et al 2007). In particular, these studies described the utilisation of different gases to modify the oxidoreduction potential of yeast environment but the effects of Eh and the gas used to modify the Eh were almost ambiguous.…”

Gaseous environments modify physiology in the brewing yeastSaccharomyces cerevisiaeduring batch alcoholic fermentation

“…2002), Yarrowia lipolytica (Husson et al. 2006) and more recently Sporidiobolus ruinenii (Feron et al. 2007).…”

“…In yeast, few studies have described the influence of redox environment on physiology of S. cerevisiae , Yarrowia lipolytica (Husson et al 2006) and more recently Sporidiobolus ruinenii (Feron et al 2007). Husson et al (2006) showed that reducing conditions were favourable to hydroperoxide lyase (HPL) synthesis as well as its activity but it was unfavourable to yeast growth.…”