Genetic and
enological analyses of a genetically enhanced malolactic wine yeast strain: A
new era in wine making.
Hennie J.J. van Vuuren, George K. van der Merwe, John Husnik
Wine Research Centre, University of British Columbia, 2205 East Mall,
Vancouver, V6T 1Z4, Canada (hjjvv@interchange.ubc.ca)
Despite the fact that most wineries use commercial starter cultures of the bacterium O. oeni, many problems exist causing delays in cellar operations and spoilage of wines, including the production of allergens. We have constructed a malolactic wine yeast by integrating the S. pombe malate transport gene and the O. oeni malolactic gene into the URA3 locus of an industrial strain of S. bayanus (Prise de Mousse). The malolactic yeast is genetically stable and does not contain any antibiotic resistance marker genes. Wine making trials showed the yeast to be efficient for malolactic fermentation and 9 g/L of malate was degraded in four days in Chardonnay grape must. The wine was superior to wine produced with parental yeast and malolactic bacteria. Use of the malolactic yeast in red wine production enhanced colour. The yeast has now been extensively tested and the malolactic cassette inserted into the genome has been fully sequenced. DNA array analysis showed that the integration of the malolactic cassette affected the expression of only 15 out of more than 6000 genes more than two-fold. Introduction of the malolactic cassette did not confer any growth or survival advantage on the malolactic yeast. Contamination studies showed that at least 10% of the yeast population had to be malolactic yeast before any malate was consumed. Use of the genetically enhanced malolactic yeast in commercial wineries presents a clear health benefit to the consumer and major benefits to wineries.