RNA sequencing reveals metabolic and regulatory changes leading to more robust fermentation performance during short-term adaptation of Saccharomyces cerevisiae to lignocellulosic inhibitors.

Background: The limited tolerance of Saccharomyces cerevisiae to inhibitors is a major challenge in second-generation bioethanol production, and our understanding of the molecular mechanisms providing tolerance to inhibitor-rich lignocellulosic hydrolysates is incomplete. Short-term adaptation of the yeast in the presence of dilute hydrolysate can improve its robustness and productivity during subsequent fermentation.

Results: We utilized RNA sequencing to investigate differential gene expression in the industrial yeast strain CR01 during short-term adaptation, mimicking industrial conditions for cell propagation.

Nutrient-supplemented propagation of Saccharomyces cerevisiae improves its lignocellulose fermentation ability.

Propagation conditions have been shown to be of considerable importance for the fermentation ability of Saccharomyces cerevisiae. The limited tolerance of yeast to inhibitors present in lignocellulosic hydrolysates is a major challenge in second-generation bioethanol production. We have investigated the hypothesis that the addition of nutrients during propagation leads to yeast cultures with improved ability to subsequently ferment lignocellulosic materials.

Strain-dependent variance in short-term adaptation effects of two xylose-fermenting strains of Saccharomyces cerevisiae.

The limited tolerance of Saccharomyces cerevisiae to the inhibitors present in lignocellulosic hydrolysates is a major challenge in second-generation bioethanol production. Short-term adaptation of the yeast to lignocellulosic hydrolysates during cell propagation has been shown to improve its tolerance, and thus its performance in lignocellulose fermentation. The aim of this study was to investigate the short-term adaptation effects in yeast strains with different genetic backgrounds.

Metabolic engineering strategies for optimizing acetate reduction, ethanol yield and osmotolerance in S.

Background: Glycerol, whose formation contributes to cellular redox balancing and osmoregulation in , is an important by-product of yeast-based bioethanol production. Replacing the glycerol pathway by an engineered pathway for NAD-dependent acetate reduction has been shown to improve ethanol yields and contribute to detoxification of acetate-containing media. However, the osmosensitivity of glycerol non-producing strains limits their applicability in high-osmolarity industrial processes.

Improving ethanol yield in acetate-reducing Saccharomyces cerevisiae by cofactor engineering of 6-phosphogluconate dehydrogenase and deletion of ALD6.

Background: Acetic acid, an inhibitor of sugar fermentation by yeast, is invariably present in lignocellulosic hydrolysates which are used or considered as feedstocks for yeast-based bioethanol production. Saccharomyces cerevisiae strains have been constructed, in which anaerobic reduction of acetic acid to ethanol replaces glycerol formation as a mechanism for reoxidizing NADH formed in biosynthesis. An increase in the amount of acetate that can be reduced to ethanol should further decrease acetic acid concentrations and enable higher ethanol yields in industrial processes based on lignocellulosic feedstocks.

Replacement of the initial steps of ethanol metabolism in Saccharomyces cerevisiae by ATP-independent acetylating acetaldehyde dehydrogenase.

In Saccharomyces cerevisiae ethanol dissimilation is initiated by its oxidation and activation to cytosolic acetyl-CoA. The associated consumption of ATP strongly limits yields of biomass and acetyl-CoA-derived products. Here, we explore the implementation of an ATP-independent pathway for acetyl-CoA synthesis from ethanol that, in theory, enables biomass yield on ethanol that is up to 40% higher.