Yeast Genetic Manipulation

Abstract

The importance of the molecular biology of S. cerevisiae is closely related species is well documented. This yeast was the first microorganism to be domesticated for the production of fermented food and beverages and to be described as a living biochemical agent for biological transformations. In 1996, the complete genome of S. cerevisiae haploid strain became the first eukaryote genome to be fully sequenced. Its 16 chromosomes encode approximately 6000 genes, and approximately 5000 of them are individually non-essential to the yeast cell. This publicly available genome sequence has prepared the way to build the first systematic collection of deletion mutants, which enables high-throughput functional genetic experiments. In 2014, S. cerevisiae became the first eukaryote to be equipped with a functional chromosome. S. cerevisiae has three basic mating types – a, α and a/α. Most laboratory strains are haploid or diploid, whereas industrial yeast strains (brewing, distilling, baking and wine) are predominantly diploid, aneuploid and polyploidy. Polyploid strains are genetically more stable and less susceptible to mutational forces than either haploid or diploid strains, thus enabling such strains to be used by brewers with a high degree of confidence. Cells of polyploid (aneuploid) brewing strains – ale and lager – sporulate poorly, and asci containing four spores rarely develop. Moreover, spore viabilities are low, and the spores that are viable often lack the ability to mate. As a consequence, alternative methods of genetic manipulation such as protoplast (spheroplast) fusion and rare mating that introduces foreign genetic material into the genome have been required to facilitate strain improvement. Unlike the other techniques discussed, genetic engineering (recombinant DNA-rDNA) affords the possibility of introducing additional factors. Also, genetic engineering methods permit the transfer of genetic information between completely unrelated organisms. Consequently, the recipient organism becomes able to produce heterologous proteins or peptides that are not produced by their mated constituents. This provides considerable scope for the transfer of new constituents into industrial yeast strains.