VTT Technical Research Centre of Finland, Espoo, Finland
Department of Biotechnology and Chemical Technology, Aalto University, School of Chemical Technology, Aalto, Espoo, Finland.
Appl Environ Microbiol. 2018 Jan 31;84(4). doi: 10.1128/AEM.02302-17. Print 2018 Feb 15.
Interspecific hybridization is a valuable tool for developing and improving brewing yeast in a number of industry-relevant aspects. However, the genomes of newly formed hybrids can be unstable. Here, we exploited this trait by adapting four brewing yeast strains, three of which were interspecific lager hybrids with different ploidy levels, to high ethanol concentrations in an attempt to generate variant strains with improved fermentation performance in high-gravity wort. Through a batch fermentation-based adaptation process and selection based on a two-step screening process, we obtained eight variant strains which we compared to the wild-type strains in 2-liter-scale wort fermentations replicating industrial conditions. The results revealed that the adapted variants outperformed the strains from which they were derived, and the majority also possessed several desirable brewing-relevant traits, such as increased ester formation and ethanol tolerance, as well as decreased diacetyl formation. The variants obtained from the polyploid hybrids appeared to show greater improvements in fermentation performance than those derived from diploid strains. Interestingly, it was not only the hybrid strains, but also the parent strain, that appeared to adapt and showed considerable changes in genome size. Genome sequencing and ploidy analysis revealed that changes had occurred at both the chromosome and single nucleotide levels in all variants. Our study demonstrates the possibility of improving lager yeast hybrids through adaptive evolution by generating stable and superior variants that possess traits relevant to industrial lager beer fermentation. Recent studies have shown that hybridization is a valuable tool for creating new and diverse strains of lager yeast. Adaptive evolution is another strain development tool that can be applied in order to improve upon desirable traits. Here, we apply adaptive evolution to newly created lager yeast hybrids by subjecting them to environments containing high ethanol levels. We isolated and characterized a number of adapted variants which possess improved fermentation properties and ethanol tolerance. Genome analysis revealed substantial changes in the variants compared to the original strains. These improved variant strains were produced without any genetic modification and are suitable for industrial lager beer fermentations.
种间杂交是在许多与工业相关的方面开发和改进酿造酵母的有价值的工具。然而，新形成的杂种的基因组可能不稳定。在这里，我们利用了这一特性，使四种酿造酵母菌株适应高乙醇浓度，其中三种是不同倍性水平的种间拉格杂种，试图在高浓度麦芽汁中产生具有改进发酵性能的变异菌株。通过基于分批发酵的适应过程和基于两步筛选过程的选择，我们获得了 8 个变异菌株，并在复制工业条件的 2 升规模麦芽汁发酵中与野生型菌株进行了比较。结果表明，适应的变体比它们的原始菌株表现更好，而且大多数变体还具有一些理想的酿造相关特性，例如增加酯形成和乙醇耐受性，以及减少双乙酰形成。从多倍体杂种获得的变体似乎比从二倍体菌株获得的变体在发酵性能方面表现出更大的改进。有趣的是，不仅是杂种菌株，而且还有亲本菌株，似乎适应了并且在基因组大小方面发生了相当大的变化。基因组测序和倍性分析表明，所有变体在染色体和单核苷酸水平都发生了变化。我们的研究表明，通过产生具有与工业拉格啤酒发酵相关的特性的稳定和优越的变体，可以通过适应性进化来改进拉格酵母杂种，这是可能的。最近的研究表明，杂交是创建新的和多样化的拉格酵母菌株的有价值的工具。适应性进化是另一种可以应用于改进所需特性的菌株开发工具。在这里，我们通过使它们适应含有高乙醇水平的环境，将适应性进化应用于新创建的拉格酵母杂种。我们分离并表征了一些具有改进发酵性能和乙醇耐受性的适应变体。与原始菌株相比，基因组分析显示变体发生了大量变化。这些改进的变体菌株是在没有任何遗传修饰的情况下生产的，适用于工业拉格啤酒发酵。
