Abstract
During fermentation, yeast cells encounter a number of stresses, including hyperosmolarity, high ethanol concentration, and high temperature. Previous deletome analysis in the yeast Saccharomyces cerevisiae has revealed that SOD1 gene encoding cytosolic Cu/Zn-superoxide dismutase (SOD), a major antioxidant enzyme, was required for tolerances to not only oxidative stress but also other stresses present during fermentation such as osmotic, ethanol, and heat stresses. It is therefore possible that these fermentation-associated stresses may also induce endogenous oxidative stress. In this study, we show that osmotic, ethanol, and heat stresses promoted generation of intracellular reactive oxygen species (ROS) such as superoxide anion in the cytosol through a mitochondria-independent mechanism. Consistent with this finding, cytosolic Cu/Zn-SOD, but not mitochondrial Mn-SOD, was required for protection against oxidative stress induced by these fermentation-associated stresses. Furthermore, supplementation of ROS scavengers such as N-acetyl-L-cysteine (NAC) alleviated oxidative stress induced during very high gravity (VHG) fermentation and enhanced fermentation performance at both normal and high temperatures. In addition, NAC also plays an important role in maintaining the Cu/Zn-SOD activity during VHG fermentation. These findings suggest the potential role of ROS scavengers for application in industrial-scale VHG ethanol fermentation.
Highlights
Due to rapid industrialization and urbanization in many countries, global energy demand has dramatically increased in recent years
Since our data suggest that Cu/Zn-superoxide dismutase (SOD) is required for protecting yeast cells against cytosolic reactive oxygen species (ROS) induced by fermentation-associated stresses, we investigated the role of Cu/Zn-SOD during very high gravity (VHG)
Since our results suggest the effect of ROS scavengers such as NAC on inhibiting endogenous oxidative stress induced during VHG fermentation, we investigated the role of NAC in promoting VHG fermentation performance of the wild-type (BY4742) strain incubated in YPD30 media at 30 and 40 °C up to 48 h
Summary
Due to rapid industrialization and urbanization in many countries, global energy demand has dramatically increased in recent years. In an industrial-scale ethanol production, the fermentation temperature is maintained by using cooling systems, heat generated by yeast metabolism and/or high environmental temperature could occasionally raise the fermentation temperature beyond an optimal range[7]. Our previous deletome analysis has revealed that SOD1 gene encoding cytosolic Cu/Zn-superoxide dismutase (SOD), one of important antioxidant enzymes, was required for tolerances to oxidative stress and other stresses present during fermentation such as ethanol, osmotic, and heat stresses[9]. Among these fermentation-associated stresses, ethanol stress has been demonstrated to induce an increased generation of reactive oxygen species (ROS)[10]. Dynamic changes in intracellular ROS levels during ethanol fermentation were monitored and the role of ROS scavenger supplementation in enhancing performances of VHG ethanol fermentation was evaluated
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