Genetic Manipulation Of Brewing Yeasts: Challenges And Opportunities

Brewing yeasts are notoriously difficult to work with genetically due to their complex genomes, which are often polyploid, aneuploid, and/or derived from interspecific hybridization events. We discuss the possibilities for both traditional and non-traditional genetic manipulations of brewing yeasts as a way to combine or enhance beneficial traits already present in such yeasts, or to possibly identify and introduce novel traits from non-brewing yeasts. For genetically tractable yeast strains, classic genetic breeding via meiosis and direct mating of spores can increase genetic variability and combine desired traits. For intractable strains, non-traditional breeding methods such as rare-mating, mating by transient HO induction, cytoduction, and protoplast fusion can be utilized. These various techniques can also be performed using mixed populations in a 'mass-mating' manner and/or to create interspecific hybrids. Once cells or populations with increased genetic variability are obtained, genome shuffling can create novel combinations of traits; adaptive evolution of shuffled populations allows the eventual selection of strains that exhibit desired fermentation or other selectable characteristics, while high-throughput quantitative trait loci (QTL) analysis can lead to insights about the actual genes that contribute to the traits of interest. The above techniques yield non-genetically modified (non-GM) yeasts. However, recent advances in 'minimally invasive' GM techniques that result in precise genome modifications with no remaining foreign DNA may eventually be deemed as acceptable by consumers and the brewing industry as a way to obtain brewing yeasts with desired traits. Overall, there is a wide variety of tools available for the genetic manipulation of brewing yeasts to alter or enhance any of a number of characteristics, from fermentation behaviour to sensory profile.