Institute of Technology, University of Tartu, Tartu, Estonia.
Appl Environ Microbiol. 2021 Jun 11;87(13):e0310020. doi: 10.1128/AEM.03100-20.
Biotechnology requires efficient microbial cell factories. The budding yeast Saccharomyces cerevisiae is a vital cell factory, but more diverse cell factories are essential for the sustainable use of natural resources. Here, we benchmarked nonconventional yeasts Kluyveromyces marxianus and Rhodotorula toruloides against S. cerevisiae strains CEN.PK and W303 for their responses to potassium and sodium salt stress. We found an inverse relationship between the maximum growth rate and the median cell volume that was responsive to salt stress. The supplementation of K to CEN.PK cultures reduced Na toxicity and increased the specific growth rate 4-fold. The higher K and Na concentrations impaired ethanol and acetate metabolism in CEN.PK and acetate metabolism in W303. In R. toruloides cultures, these salt supplementations induced a trade-off between glucose utilization and cellular aggregate formation. Their combined use increased the beta-carotene yield by 60% compared with that of the reference. Neural network-based image analysis of exponential-phase cultures showed that the vacuole-to-cell volume ratio increased with increased cell volume for W303 and K. marxianus but not for CEN.PK and R. toruloides in response to salt stress. Our results provide insights into common salt stress responses in yeasts and will help design efficient bioprocesses. Characterization of microbial cell factories under industrially relevant conditions is crucial for designing efficient bioprocesses. Salt stress, typical in industrial bioprocesses, impinges upon cell volume and affects productivity. This study presents an open-source neural network-based analysis method to evaluate volumetric changes using yeast optical microscopy images. It allows quantification of cell and vacuole volumes relevant to cellular physiology. On applying salt stress in yeasts, we found that the combined use of K and Na improves the cellular fitness of Saccharomyces cerevisiae strain CEN.PK and increases the beta-carotene productivity in Rhodotorula toruloides, a commercially important antioxidant and a valuable additive in foods.
生物技术需要高效的微生物细胞工厂。出芽酵母酿酒酵母是一种重要的细胞工厂，但更具多样性的细胞工厂对于可持续利用自然资源至关重要。在这里，我们将非常规酵母马克斯克鲁维酵母和罗伦隐球酵母与酿酒酵母菌株 CEN.PK 和 W303 进行基准测试，以评估它们对钾盐和钠盐胁迫的反应。我们发现最大生长速率与对盐胁迫有响应的细胞体积中位数之间存在反比关系。向 CEN.PK 培养物中添加 K 可降低 Na 毒性并将比生长速率提高 4 倍。较高的 K 和 Na 浓度会损害 CEN.PK 中的乙醇和乙酸盐代谢以及 W303 中的乙酸盐代谢。在 R. toruloides 培养物中，这些盐的添加会在葡萄糖利用和细胞聚集体形成之间产生权衡。与对照相比，它们的联合使用将β-胡萝卜素的产量提高了 60%。指数生长期培养物的基于神经网络的图像分析表明，W303 和 K. marxianus 的液泡与细胞体积比随着细胞体积的增加而增加，但 CEN.PK 和 R. toruloides 则不然。这些结果提供了关于酵母中常见盐胁迫反应的见解，并将有助于设计高效的生物工艺。在工业相关条件下对微生物细胞工厂进行表征对于设计高效的生物工艺至关重要。盐胁迫是工业生物工艺中的典型现象，会影响细胞体积并影响生产力。本研究提出了一种基于神经网络的开源分析方法，使用酵母光学显微镜图像来评估体积变化。它允许量化与细胞生理相关的细胞和液泡体积。在酵母中施加盐胁迫时，我们发现 K 和 Na 的联合使用可提高酿酒酵母菌株 CEN.PK 的细胞适应性，并提高罗伦隐球酵母的β-胡萝卜素生产力，罗伦隐球酵母是一种商业上重要的抗氧化剂，也是食品中的一种有价值的添加剂。
