Identification of Yeast Strain Genetic Factors in the Formation of Volatile

In this past grant year two significant sub-objectives of this proposal were completed. First, the studies to determine the synthetic juice conditions best mimicking natural grape juice were completed and the twelve yeast strains for the rest of the study were selected from the extensive analysis of the initial 29. The selected strains display a broad array of behaviors with respect to hydrogen sulfide formation under enological conditions. This body of work has been submitted as a manuscript. The second major sub-objective to be completed was the comparison of the Microarray and Proteome technologies for analysis of global gene expression. The microarray analysis profiles the pattern of expression of mRNA, the “transcriptome”, while the proteome analysis directly profiles protein patterns. Both techniques suffer from limitations that may be particularly severe depending upon the relative level of expression of the genes of interest. It was necessary to compare both techniques to determine which one would be most useful for the comparative analysis of expression of proteins of the sulfate reduction pathway. The microarray analysis allows accurate quantitation and comparison of moderately to lowly expressed mRNA species, but is not useful for comparative analyses of highly expressed mRNA species. The mRNAs for the genes of the sulfate reduction pathway were found to be for the most part too highly expressed to be accurately estimated with this technology. However, as described in detail below, the microarray analysis did provide extremely useful information on the physiological status of the cells during nitrogen limitation. The strain used for this study was an isolate of the commercial French White strain. On the other hand, the Proteome analysis was found to be quite suitable for this study. The major proteins of interest are all visible as distinct spots on the proteome gels. In the past year we have fine-tuned this protocol and have achieved better reproducibility than what is typically reported in the literature. The direct comparison of the protein profiles of strains displaying differences in H2S formation has been initiated and will continue next year.