Fermentative capacity of dry active wine yeast requires a specific oxidative stress response during industrial biomass growth

Abstract

Induction of the oxidative stress response has been described under many physiological conditions in Saccharomyces cerevisiae, including industrial fermentation for wine yeast biomass production where cells are grown through several batch and fed-batch cultures on molasses. Here, we investigate the influence of aeration on the expression changes of different gene markers for oxidative stress and compare the induction profiles to the accumulation of several intracellular metabolites in order to correlate the molecular response to physiological and metabolic changes. We also demonstrate that this specific oxidative response is relevant for wine yeast performance by construction of a genetically engineered wine yeast strain overexpressing the TRX2 gene that codifies a thioredoxin, one of the most important cellular defenses against oxidative damage. This modified strain displays an improved fermentative capacity and lower levels of oxidative cellular damages than its parental strain after dry biomass production.

Recent Advances in Yeast Biomass Production

“…Alcoholic fermentation leads to a suboptimal biomass concentration because the ATP yield is much lower than the yield obtained during respiratory carbohydrate degradation (Verduyn, 1991;Rizzi et al, 1997). However, pre-adaptation to large amounts of glucose during the batch phase is necessary to ensure the produced biomass' optimal fermentative capacity by accumulating several necessary reserve metabolites to be used in the fedbatch phase (Dombek and Ingram, 1987;Rizzi et al, 1997;Pérez-Torrado et al, 2009). In www.intechopen.com addition, prolonged growth in aerobic, glucose-limited chemostat cultures of S. cerevisiae, avoiding the batch phase, causes a partial loss of glycolytic capacity (Jansen et al, 2005).…”

“…In the transition to the respiratory phase, an increase in the cAMP levels triggers the breakdown of storage carbohydrates and an increased influx of glucose into the glycolytic pathway. The resulting increase in the NAD + /NADH ratio stimulates respiration in combination with a drop in the ATP level, which is consumed mainly during biomass formation (Pérez-Torrado, 2004;Xu and Tsurugi, 2006;Pérez-Torrado et al, 2009). In some industrial wine yeast production plants, fed-batch phases are initiated without consuming ethanol from the growth media, which considerably reduces the biomass yield.…”

“…However the presence of O 2 from the beginning of the process allows yeast cells to synthesise lipids, thereby revitalising the sterol-deficient cell population and ensuring that fermentation can proceed efficiently. Besides, those propagation experiments carried out in non-oxygenated media considerably reduce yeast growth and increase internal oxidative stress (Boulton, 2000;Pérez-Torrado et al, 2009). During batch fermentation (F2-F4), a growth lag phase takes place in which cells synthesise the enzymes involved in gluconeogenesis and the glyoxylate cycle (Haarasilta and Oura, 1975).…”

“…(Garre et al, 2010). As a result, these dynamic environmental injuries seriously affect biomass yield, fermentative capacity, vitality, and cell viability (Attfield, 1997;Pretorius, 1997;Pérez-Torrado et al, 2005;Pérez-Torrado et al, 2009). …”

Oxidative stress in fungal fermentation processes: the roles of alternative respiration

“…Such studies have a measure of success, for example, in over-expression of genes coding for antioxidant enzymes such as catalase (Abbott et al 2009) and thioredoxin (Perez-Torrado et al 2009), introduction of genes for synthesis of antioxidants such as vitamin C (Branduardi et al 2007) and astaxanthin (Ukibe et al 2009) all increase yeast cells' resistance to oxidative stress. Provided the genetic alterations made to these strains do not reduce vigour, or lead to altered proteolysis, such mutants could have clear advantages in industrial fermentation where oxidative stress is encountered.…”