Eoin Moynihan (1); (1) University Of Nottingham, Nottingham, U.K.

Yeast, Fermentation, and Microbiology

Until recently the role of yeast mitochondria in brewing fermentation has been poorly understood. This is primarily because mitochondrial function is associated with cellular respiration, which is itself minimized during fermentation due to a combination of the Crabtree effect and predominantly anaerobic conditions. However, current understanding is that yeast mitochondria are essential for cellular function and fermentation performance, due to a number of important characteristics, including their role in nuclear DNA signaling, acetyl-CoA synthesis and lipid generation. This is supported by the fact that cells lacking in mitochondrial function, termed respiratory deficient or “petites,” do not ferment as well as wild-type cells. Fermentations conducted using cultures comprising an abnormal number of petites are typically slow, with a poor conversion of sugar to alcohol. In addition, such yeast cultures display reduced growth, abnormal flocculation characteristics, and poor VDK reduction capabilities, while the final product is often characterized by irregular flavor profiles. Generation of the petite phenotype is complex, and if a critical number of mitochondria are either defective (Rho) or absent (Rho0), the individual cell will become respiratorily incompetent. Conversely, it can be considered that a certain number of mitochondria should be present and able to function correctly in order for a cell to function as normal. In this study we aim to determine the effect of process conditions on the number of mitochondria present within cells, with the primary goal of establishing some of the key causes behind petite generation. This may provide insight as to why some industrial strains have a higher propensity to form petite mutants than others, and which aspects of yeast handling have the biggest influence on promoting petite generation. It is anticipated that by furthering our understanding of the petite mutation it will be possible to reduce or mitigate their impact on brewery fermentations.

Eoin Moynihan is an SABMiller-funded Ph.D. student at the International Centre for Brewing Science at the University of Nottingham, UK. Eoin holds a B.S. (honors) degree in plant biotechnology (2009) and an M.S. degree in applied biotechnology (2013), both obtained at the University College of Cork, Ireland. During his M.S. degree studies, he focused on yeast diversity throughout spontaneous cider production and began his current project examining the role of mtDNA in brewing yeast in 2015.