Weina Xu, Jiangnan University, Wuxi, Jiangsu Province, China
ABSTRACT: Yeast is the soul of beer fermentation. During fermentation, yeast produces numerous beer flavor compounds, including esters, acetaldehyde, and higher alcohols. At the same time, some other characteristics of brewer’s yeast, such as cell age, fermentation rate, and flocculation, are also important in the brewing industry. Brewer’s yeast has a decisive influence on beer fermentation. Most industrial brewer’s yeasts are lager yeasts and are generally natural genetic hybrids, heterothallic polyploidies, or aneuploidies. Their intricate ploidies present a great challenge to genetic studies and strain improvement. Haploid breeding is an effective method to overcome these difficulties. In this study, we established a systematic method to induce, separate, and identify haploid strains of industrial brewer’s yeast. Firstly, efficient sporulation medium was selected to induce sporulation of industrial brewer’s yeast strain G-03. Then spores were isolated from vegetative cells and formed colonies on YPD plates. Flow cytometry was employed to determine the ploidy types of the pre-judged haploid candidates. The genotypes were analyzed by PCR for the MAT locus and mating test. Using this protocol, 26 yeast strains were obtained by spore isolation. Four that were pre-judged as haploid candidates were finally confirmed as haploid by flow cytometric analysis, two of them were MATa, and others were MATalpha. This protocol proved practical for breeding haploid strains of other industrial brewer’s yeasts as well.
Weina Xu received a B.E. degree in bioengineering from Dalian University and is currently a doctoral student in fermentation engineering at Jiangnan University. She has studied microbiology for several years, and now is devoting herself to the breeding and improving of brewer’s yeasts.