A new laboratory evolution approach to select for constitutive acetic acid tolerance in Saccharomyces cerevisiae and identification of causal mutations.

Background: Acetic acid, released during hydrolysis of lignocellulosic feedstocks for second generation bioethanol production, inhibits yeast growth and alcoholic fermentation. Yeast biomass generated in a propagation step that precedes ethanol production should therefore express a high and constitutive level of acetic acid tolerance before introduction into lignocellulosic hydrolysates. However, earlier laboratory evolution strategies for increasing acetic acid tolerance of Saccharomyces cerevisiae, based on prolonged cultivation in the presence of acetic acid, selected for inducible rather than constitutive tolerance to this inhibitor.

The fraction of cells that resume growth after acetic acid addition is a strain-dependent parameter of acetic acid tolerance in Saccharomyces cerevisiae.

High acetic acid tolerance of Saccharomyces cerevisiae is a relevant phenotype in industrial biotechnology when using lignocellulosic hydrolysates as feedstock. A screening of 38 S. cerevisiae strains for tolerance to acetic acid revealed considerable differences, particularly with regard to the duration of the latency phase.

Genome-scale analyses of butanol tolerance in Saccharomyces cerevisiae reveal an essential role of protein degradation.

Background: n-Butanol and isobutanol produced from biomass-derived sugars are promising renewable transport fuels and solvents. Saccharomyces cerevisiae has been engineered for butanol production, but its high butanol sensitivity poses an upper limit to product titers that can be reached by further pathway engineering. A better understanding of the molecular basis of butanol stress and tolerance of S.

A new methodology to obtain wine yeast strains overproducing mannoproteins.

Yeast mannoproteins are highly glycosylated proteins that are covalently bound to the beta-1,3-glucan present in the yeast cell wall. Among their outstanding enological properties, yeast mannoproteins contribute to several aspects of wine quality by protecting against protein haze, reducing astringency, retaining aroma compounds and stimulating growth of lactic-acid bacteria. The development of a non-recombinant method to obtain enological yeast strains overproducing mannoproteins would therefore be very useful.

Construction of a recombinant autolytic wine yeast strain overexpressing the csc1-1 allele.

During the aging step of sparkling wines and wines aged on lees, yeast cells kept in contact with the wine finally die and undergo autolysis, releasing cellular compounds with a positive effect on the wine quality. In view of the interest of autolysis for wine properties, biotechnologists have tried to improve autolytic yield during winemaking. In this work we used genetic engineering techniques to construct an autolytic industrial strain by expressing the csc1-1 allele from the RDN1 locus.

Three different targets for the genetic modification of wine yeast strains resulting in improved effectiveness of bentonite fining.

Bentonite fining is used in the clarification of white wines to prevent protein haze. This treatment results in the loss of a significant portion of the wine itself, as well as aroma compounds important for the quality of white wines. Among other interesting effects on wine quality, yeast cell wall mannoproteins have been shown to stabilize wine against protein haze.

A recombinant Saccharomyces cerevisiae strain overproducing mannoproteins stabilizes wine against protein haze.

Stabilization against protein haze was one of the first positive properties attributed to yeast mannoproteins in winemaking. In previous work we demonstrated that deletion of KNR4 leads to increased mannoprotein release in laboratory Saccharomyces cerevisiae strains. We have now constructed strains with KNR4 deleted in two different industrial wine yeast backgrounds.

Genetic determinants of the release of mannoproteins of enological interest by Saccharomyces cerevisiae.

Cell wall mannoproteins released by Saccharomyces cerevisiae during wine fermentation and aging have recently attracted the attention of enologists and researchers in enology due to their positive effect over a number of technological and quality properties of the wines, including protein and tartaric stability, aroma and color stability, astringency, mouthfeel, malolactic fermentation, or foam properties of sparkling wines. This work has investigated the effect of deletions involving genes related to cell wall biogenesis on the release of mannoproteins, as well as the effect of the released mannoproteins on wine protein stability. When available, the phenotypes have been studied in different genetic backgrounds, in haploid or diploid strains, and in homo- or heterozygosis.

Transgenic wine yeast technology comes of age: is it time for transgenic wine?

Saccharomyces cerevisiae is the main yeast responsible for alcoholic fermentation of grape juice during wine making. This makes wine strains of this species perfect targets for the improvement of wine technology and quality. Progress in winemaking has been achieved through the use of selected yeast strains, as well as genetic improvement of wine yeast strains through the sexual and pararexual cycles, random mutagenesis and genetic engineering.