Thermotolerant Yeast Strains Adapted by Laboratory Evolution Show Trade-Off at Ancestral Temperatures and Preadaptation to Other Stresses.
Thermotolerant Yeast Strains Adapted by Laboratory Evolution Show Trade-Off at Ancestral Temperatures and Preadaptation to Other Stresses.
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DOI：
10.1128/mbio.00431-15
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发表时间：
2015-07-21
期刊：
影响因子：
6.4
通讯作者：
Nielsen J
中科院分区：
文献类型：
--
作者：
Caspeta L;Nielsen J
从生物质衍生的原料生产乙醇的主要挑战是开发可以在生产过程中存在的各种抑制条件下维持生长的酵母，例如，高渗透压摩尔浓度、高乙醇滴度和/或高温（≥40°C）。使用适应性实验室进化，我们先前分离出七种在40°C下生长改善的酿酒酵母菌株。在这里，我们表明，对高温的遗传适应导致了在祖先温度下的生长权衡，降低了细胞功能，并提高了对其他胁迫的耐受性。耐热酵母菌株表现出水平位移的热反应规范，以更高的温度。因此，它们的最佳和最大生长温度增加了约3°C，而它们在低于34°C的温度下显示出生长权衡。对蛋白质物理性质的计算分析表明，酵母的致死温度约为49°C，因为大部分酵母蛋白质在此温度以上变性。我们的分析还表明，与祖先菌株相比，耐热菌株中参与控制生长速率的功能数量减少。后者是获得耐热性的有利属性，并且与呼吸能力丧失相关的酵母功能的降低相关。这种特性导致甘油生产过剩，这与祖先温度下的生长权衡有关。结合改变固醇组成的细胞膜，甘油的过度生产也与酵母菌的耐药性和高浓度的葡萄糖和乙醇的耐受性改善。我们的研究表明，酵母的热适应是适合于提高酵母抵抗工业乙醇生产过程中发现的抑制条件。酵母耐热性可以显著降低生物质转化为乙醇的生产成本。然而，关于酵母耐热性所需的潜在遗传变化和生理功能的信息很少。最近，我们揭示了通过适应性实验室进化产生的耐热酵母菌株（TTS）的耐热性的遗传变化。在这里，我们研究了这些TTS的生理学，并计算了它们在整个热生态位上的蛋白质组稳定性，以及它们对其他压力的预适应。使用这种方法，我们表明，TTTS表现出进化的权衡在祖先的热生态位，以及减少的数量的生长功能和预适应乙醇生产过程中发现的其他压力。这一信息将是有用的合理工程酵母耐热性的生产生物燃料和化学品。
A major challenge for the production of ethanol from biomass-derived feedstocks is to develop yeasts that can sustain growth under the variety of inhibitory conditions present in the production process, e.g., high osmolality, high ethanol titers, and/or elevated temperatures (≥40°C). Using adaptive laboratory evolution, we previously isolated seven Saccharomyces cerevisiae strains with improved growth at 40°C. Here, we show that genetic adaptations to high temperature caused a growth trade-off at ancestral temperatures, reduced cellular functions, and improved tolerance of other stresses. Thermotolerant yeast strains showed horizontal displacement of their thermal reaction norms to higher temperatures. Hence, their optimal and maximum growth temperatures increased by about 3°C, whereas they showed a growth trade-off at temperatures below 34°C. Computational analysis of the physical properties of proteins showed that the lethal temperature for yeast is around 49°C, as a large fraction of the yeast proteins denature above this temperature. Our analysis also indicated that the number of functions involved in controlling the growth rate decreased in the thermotolerant strains compared with the number in the ancestral strain. The latter is an advantageous attribute for acquiring thermotolerance and correlates with the reduction of yeast functions associated with loss of respiration capacity. This trait caused glycerol overproduction that was associated with the growth trade-off at ancestral temperatures. In combination with altered sterol composition of cellular membranes, glycerol overproduction was also associated with yeast osmotolerance and improved tolerance of high concentrations of glucose and ethanol. Our study shows that thermal adaptation of yeast is suitable for improving yeast resistance to inhibitory conditions found in industrial ethanol production processes. Yeast thermotolerance can significantly reduce the production costs of biomass conversion to ethanol. However, little information is available about the underlying genetic changes and physiological functions required for yeast thermotolerance. We recently revealed the genetic changes of thermotolerance in thermotolerant yeast strains (TTSs) generated through adaptive laboratory evolution. Here, we examined these TTSs’ physiology and computed their proteome stability over the entire thermal niche, as well as their preadaptation to other stresses. Using this approach, we showed that TTSs exhibited evolutionary trade-offs in the ancestral thermal niche, as well as reduced numbers of growth functions and preadaptation to other stresses found in ethanol production processes. This information will be useful for rational engineering of yeast thermotolerance for the production of biofuels and chemicals.