Gordon A. Walker

University of California, Davis | UCD · Department of Viticulture and Enology

In experimental science, organisms are usually studied in isolation, but in the wild, they compete and cooperate in complex communities. We report a system for cross-kingdom communication by which bacteria heritably transform yeast metabolism. An ancient biological circuit blocks yeast from using other carbon sources in the presence of glucose. [ G...

The efficiency and efficacy of alcoholic fermentation by yeast is crucial for the winemaking process. Sluggish or arrested fermentations can negatively affect winery operations and wine quality. Here, we present a novel mechanism by which problem fermentations can arise. Yeast can induce a prion known as [GAR+] that allows the cell to circumvent gl...

The yeast Saccharomyces cerevisiae has evolved to dominate grape juice fermentation. A suite of cellular properties, rapid nutrient depletion, production of inhibitory compounds and the metabolic narrowing of the niche, all enable a minor resident of the initial population to dramatically increase its relative biomass in the ecosystem. This dominan...

Establishment of the [GAR⁺] prion in Saccharomyces cerevisiae reduces both transcriptional expression of the HXT3 hexose transporter gene and fermentation capacity in high sugar conditions. We evaluated the impact of deletion of the HXT3 gene on the expression of [GAR⁺] prion phenotype in a vineyard isolate, UCD932, and found that changes in fermen...

Real-time process metrics are standard for the majority of fermentation-based industries but have not been widely adopted by the wine industry. In this study, replicate fermentations were conducted with temperature as the main process parameter and assessed via in-line Oxidation Reduction Potential (ORP) probes and at-line profiling of phenolics co...

Lactobacillus kunkeei, also known as the “ferocious lactobacilli”, causes fermentation arrest during wine production1. L. kunkeei co-evolved with honeybees and is an important probiotic for bee and hive health2. In the bee ecosystem L. kunkeei is one of a suite of lactic acid bacteria that protect the bee and hive from pathogens as well as aid in p...

In Saccharomyces cerevisiae the process of transport of sugar substrates into the cell comprises a complex network of transporters and interacting regulatory mechanisms. Members of the large family of hexose (HXT) transporters display uptake efficiencies consistent with their environmental expression and play physiological roles in addition to feed...

This chapter describes the diversity of the microbial communities present throughout the process of wine production. The chapter is divided into two sections and begins by covering the microbiota found at each stage of the production process, starting with the incoming grapes and ending with a discussion of the microbes that may persist into bottli...