Transcription profile of brewery yeast under fermentation conditions T.C. James 1 , S. Campbell 1 , D. Donnelly 2 and U. Bond 1 1 Moyne Institute for Preventive Medicine, Microbiology Department, Trinity College, University of Dublin, Dublin 2, Ireland, and 2 Guinness R&D, Guinness Brewery, Dublin, Ireland 2002/133: received 25 March 2002, revised 28 October 2002 and accepted 12 November 2002 ABSTRACT T.C. JAMES, S. CAMPBELL, D. DONNELLY AND U. BOND. 2003. Aims: Yeast strains, used in the brewing industry, experience distinctive physiological conditions. During a brewing fermentation, yeast are exposed to anaerobic conditions, high pressure, high specific gravity and low temperatures. The purpose of this study was to examine the global gene expression profile of yeast subjected to brewing stress. Methods and Results: We have carried out a microarray analysis of a typical brewer’s yeast during the course of an 8-day fermentation in 15°P wort. We used the probes derived from Saccharomyces cerevisiae genomic DNA on the chip and RNA isolated from three stages of brewing. This analysis shows a high level of expression of genes involved in fatty acid and ergosterol biosynthesis early in fermentation. Furthermore, genes involved in respiration and mitochondrial protein synthesis also show higher levels of expression. Conclusions: Surprisingly, we observed a complete repression of many stress response genes and genes involved in protein synthesis throughout the 8-day period compared with that at the start of fermentation. Significance and Impact of the Study: This microarray data set provides an analysis of gene expression under brewing fermentation conditions. The data provide an insight into the various metabolic processes altered or activated by brewing conditions of growth. This study leads to future experiments whereby selective alterations in brewing conditions could be introduced to take advantage of the changing transcript profile to improve the quality of the brew. Keywords: Anaerobiosis, brewing, fermentation, lager yeast transcriptome, metabolic changes, stress response. INTRODUCTION The primary role of yeast in brewing is to catalyse the rapid and efficient conversion of wort sugars to ethanol, carbon dioxide and other minor but important metabolites without the development of off-flavours. The application of yeast in traditional biotechnology such as brewing, baking and wine making, involves their exposure to numerous environmental stresses, which can affect the vitality and viability of the culture. In the case of brewing, although not limited, these include high osmotic and hydrostatic pressure, high alcohol concentration, anaerobiosis and temperature fluctuations. Yeast exhibits a complex array of stress responses when subjected to conditions that are less than physiologically ideal (Attfield and Kletsas 2000; Carrasco et al. 2001). These responses involve aspects of cell stress sensing, signal transduction, transcription and translation, protein targeting to organelles, accumulation of stress-protectants and activa- tion of repair functions. The efficiency of these processes in a given yeast strain determines its robustness, and whether it is able to perform to necessary commercial standards in industrial brewing. Many classical and modern methods have been designed to test the efficiency of these stress responses in yeast (Kleyn and Hough 1971; Randez-Gil et al. 1999). Correspondence to: U. Bond, Moyne Institute for Preventive Medicine, Microbiology Department, Trinity College, University of Dublin, Dublin 2, Ireland (e-mail: ubond@tcd.ie). ª 2003 The Society for Applied Microbiology Journal of Applied Microbiology 2003, 94, 432–448