RESEARCH: Winemaking is stressful business and not just for the winemaker and grape grower. These two individuals are joined by a third character — the wine yeast Saccharomyces cerevisiae — whose indispensable role in the process was only recognized about 150 years ago. Stated differently, if humans have been making wine for the last 7,000 years, as suggested by archeological evidence, and we imagine these years to span a single 24-hour day, yeast's essential role would have been discovered only in the last half hour of that day! And what of the stresses of the fermentation? While this species is probably the most alcohol-tolerant organism on the planet, life during fermentation is no picnic, and in the end, accumulation of ethanol-induced damage is the most likely cause of death. This organism's love affair with sugar exposes it to great osmotic pressure as sugar concentrations in ripe grapes can easily exceed 25%. The ancient practice of adding sulfite to the fermentation as an antioxidant and mild antimicrobial agent to protect against contaminating microbes is yet another stress that yeast has learned to overcome. A successful history of adapting to environmental headaches — some a product of human domestication — combined with a wealth of available biochemical, molecular, and genomic information unmatched in any other eukaryote, has made S. cerevisiae a powerful model for discovering mechanisms that underlie the physiology of stress and adaptation. My laboratory is interested in understanding the specific contributions S. cerevisiae makes to wine quality. In addition, we have a keen interest in better understanding and overcoming the barriers that interfere with microbial-mediated conversion of plant biomass to biofuels and bioproducts. Current Projects: In vivo detoxification of acetic acid in Saccharomyces cerevisiae. Lignocellulosic biomass represents a significant potential source of renewable energy that can contribute to national transportation needs without competing for land needed for food crops. Because native lignocellulosic biomass is highly refractory to degradation, pre-treatments are needed to make the cellulose more accessible to subsequent enzymatic saccharification. Such treatments also generate high levels of compounds such as acetic acid that inhibit the subsequent fermentation, and thus impede practical development of this energy source. We are interested in exploiting the innate metabolic capacity of the yeast Saccharomyces cerevisiae to overcome acetic acid-mediated inhibition of sugar fermentation. Our central hypothesis is that acetic acid tolerance in yeast can be increased by reducing uptake, by increasing tolerance for oxidative stress, and by increasing flux through normal acetic acid-consuming pathways. Our long-term goal is to develop schemes for the biological detoxification of a variety of fermentation inhibitors generated during pre-treatments in order to increase the productivity of microbes used to convert lignocellulosic-derived sugar to ethanol and other bioproducts or biofuels. Contributions of yeast mannoproteins to wine quality. The process of aging wine on the yeast lees refers to post-fermentation aging of wine in barrel, tank, or bottle in the presence of the yeast biomass produced during vinification. The process involves simultaneous extraction of yeast components into wine and adsorption of grape constituents onto insoluble yeast cell wall fragments. The adsorbed grape constituents are eventually removed by clarification of the wine prior to bottling. The process of aging on the lees is believed to result in a net improvement in wine quality. Several benefits of aging wine on the lees have been ascribed specifically to extraction of yeast mannoproteins. For example, specific yeast mannoproteins, or fragments thereof, have been shown to enhance protein stability in white wines presumably by interfering with aggregation of grape proteins and other wine constituents that would otherwise form undesirable hazes. There is evidence that interactions between mannoproteins and tannins in red wines can improve certain sensory characteristics, e.g., astringency, texture and mouthfeel. We have recently determined that yeast mannoproteins have greater solution stability in wine than other yeast proteins and may remain in solution long enough to make a lasting contribution to improved sensory character. We are currently interested in determining the longevity of mannoproteins in aged red wines and the factors that affect their stability.