Krogerus Kristoffer, Magalhães Frederico, Castillo Sandra, Peddinti Gopal, Vidgren Virve, De Chiara Matteo, Yue Jia-Xing, Liti Gianni, Gibson Brian
VTT Technical Research Centre of Finland, Espoo, Finland.
Department of Biotechnology and Chemical Technology, Aalto University, School of Chemical Technology, Espoo, Finland.
Front Fungal Biol. 2021 Sep 16;2:733655. doi: 10.3389/ffunb.2021.733655. eCollection 2021.
Yeasts in the lager brewing group are closely related and consequently do not exhibit significant genetic variability. Here, an artificial × tetraploid interspecies hybrid was created by rare mating, and its ability to sporulate and produce viable gametes was exploited to generate phenotypic diversity. Four spore clones obtained from a single ascus were isolated, and their brewing-relevant phenotypes were assessed. These F1 spore clones were found to differ with respect to fermentation performance under lager brewing conditions (15°C, 15 °Plato), production of volatile aroma compounds, flocculation potential and temperature tolerance. One spore clone, selected for its rapid fermentation and acetate ester production was sporulated to produce an F2 generation, again comprised of four spore clones from a single ascus. Again, phenotypic diversity was introduced. In two of these F2 clones, the fermentation performance was maintained and acetate ester production was improved relative to the F1 parent and the original hybrid strain. Strains also performed well in comparison to a commercial lager yeast strain. Spore clones varied in ploidy and chromosome copy numbers, and faster wort fermentation was observed in strains with a higher ploidy. An F2 spore clone was also subjected to 10 consecutive wort fermentations, and single cells were isolated from the resulting yeast slurry. These isolates also exhibited variable fermentation performance and chromosome copy numbers, highlighting the instability of polyploid interspecific hybrids. These results demonstrate the value of this natural approach to increase the phenotypic diversity of lager brewing yeast strains.
贮藏啤酒酿造组中的酵母密切相关，因此不表现出显著的遗传变异性。在此，通过罕见交配创建了一个人工四倍体种间杂种，并利用其形成孢子和产生有活力配子的能力来产生表型多样性。从单个子囊中获得的四个孢子克隆被分离出来，并评估了它们与酿造相关的表型。发现这些F1孢子克隆在贮藏啤酒酿造条件（15°C，15°柏拉图）下的发酵性能、挥发性香气化合物的产生、絮凝潜力和温度耐受性方面存在差异。选择了一个因其快速发酵和乙酸酯产生而被选中的孢子克隆进行孢子形成以产生F2代，同样由来自单个子囊的四个孢子克隆组成。再次引入了表型多样性。在这些F2克隆中的两个中，相对于F1亲本和原始杂交菌株，发酵性能得以维持，乙酸酯产量得到提高。与商业贮藏啤酒酵母菌株相比，这些菌株也表现良好。孢子克隆的倍性和染色体拷贝数各不相同，并且在倍性较高的菌株中观察到更快的麦芽汁发酵。一个F2孢子克隆也进行了10次连续的麦芽汁发酵，并从所得酵母浆中分离出单细胞。这些分离物也表现出可变的发酵性能和染色体拷贝数，突出了多倍体种间杂种的不稳定性。这些结果证明了这种自然方法对于增加贮藏啤酒酿造酵母菌株表型多样性的价值。
