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O-26. Yeast mitochondria—Their influence on brewer’s yeast fermentation and medical research

Presenter: Graham G. Stewart, GGStewart Associates, Cardiff, U.K.

Brewer’s yeast strains (both lager and ale cultures) belong to a commercially significant grouping of yeast species that are used for the production of food, alcoholic beverages, and drugs for medicinal purposes. In addition, this yeast group is an invaluable model eukaryote because it is a single cell that can be genetically manipulated and cultured in the laboratory. The fact that it possesses a cell structure similar to plants and animals, including humans, that includes cell walls, a nucleus, vacuole(s), membranes, and mitochondria is also very important. In Saccharomyces cerevisiae and related species (including brewer’s yeast strains) the most frequent spontaneous mutation is to the specific DNA contained in its mitochondria (mtDNA). This mutation is termed respiratory deficiency (RD) or petite because of the small size of the resulting colonies compared with the respiratory sufficient variant. The phenotypic effects of the RD mutation in a brewer’s yeast culture are profound, and examples, particularly during wort fermentation, will be discussed. In addition, fundamental research on yeast mtDNA has assisted our knowledge of human mitochondrial function and disease. There is a group of diseases caused by dysfunctional mtDNA often as a result of mutation of mtDNA. These diseases include type one diabetes, deafness, hereditary optic neuropathy, and epilepsy, to name just a few. Mitochondrial research with yeast has provided considerable information and assisted medical research on many of the diseases listed above. Indeed, current research removing the mtDNA from the ovaries of a diseased patient and replacing it with unmutated mtDNA from a donor to produce healthy zygotes is a novel technique with significant potential. Importantly, in the context of this presentation, without mitochondrial research on brewer’s yeast and its close relatives, these medical developments would have been inhibited, impeded, and protracted.

Graham Stewart, emeritus professor in brewing and distilling at Heriot-Watt University, Edinburgh, Scotland, was director and professor of the International Centre for Brewing and Distilling, Heriot-Watt University, from 1994 to 2007. He received his BS. (Honors) degree in microbiology and biochemistry from the University of Wales, Cardiff, and Ph.D. and D.S. degrees from Bath University. He was a lecturer in biochemistry in the School of Pharmacy at Portsmouth College of Technology (now Portsmouth University) from 1967 to 1969. From 1969 to 1994 he held a number of technical positions with Labatt’s in Canada and from 1986 to 1994 was its brewing technical director. He was president of the Institute of Brewing (now the Institute of Brewing and Distilling) in 1999 and 2000. He is also a member of MBAA and ASBC. He holds fellowships in IBD, the Institute of Biology, and the American Academy of Microbiology. He has more than 300 publications (books, patents, review papers, articles, and peer-reviewed papers) to his name. Upon retiring he established a consulting company, GGStewart Associates, with an office in Cardiff, Wales. He was awarded the IBD Horace Brown Medal in 2008, the ASBC Award of Excellence in 2008, the MBAA Presidential Award in 1983 and 1998, the MBAA Award of Distinction in 2009, and the Society of Industrial Microbiology Charles Thom Award in 1988.

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