Qi Yanli, Liu Hui, Yu Jiayin, Chen Xiulai, Liu Liming
State Key Laboratory of Food Science and Technology, Jiangnan University, Wuxi, Jiangsu, China.
Key Laboratory of Industrial Biotechnology, Ministry of Education, Jiangnan University, Wuxi, Jiangsu, China.
Appl Environ Microbiol. 2017 Aug 31;83(18). doi: 10.1128/AEM.01128-17. Print 2017 Sep 15.
is a promising producer of organic acids. To elucidate the physiological function of the Mediator tail subunit Med15B in the response to low-pH stress, we constructed a deletion strain, Δ, and an overexpression strain, Δ/ Deletion of caused biomass production, glucose consumption rate, and cell viability to decrease by 28.3%, 31.7%, and 26.5%, respectively, compared with those of the parent (Δ) strain at pH 2.0. Expression of lipid metabolism-related genes was significantly downregulated in the Δ strain, whereas key genes of ergosterol biosynthesis showed abnormal upregulation. This caused the proportion of C fatty acids, the ratio of unsaturated to saturated fatty acids (UFA/SFA), and the total phospholipid content to decrease by 11.6%, 27.4%, and 37.6%, respectively. Cells failed to synthesize fecosterol and ergosterol, leading to the accumulation and a 60.3-fold increase in the concentration of zymosterol. Additionally, cells showed reductions of 69.2%, 11.6%, and 21.8% in membrane integrity, fluidity, and H-ATPase activity, respectively. In contrast, overexpression of Med15B increased the C levels, total phospholipids, ergosterol content, and UFA/SFA by 18.6%, 143.5%, 94.5%, and 18.7%, respectively. Membrane integrity, fluidity, and H-ATPase activity also increased by 30.2%, 6.9%, and 51.8%, respectively. Furthermore, in the absence of pH buffering, dry weight of cells and pyruvate concentrations were 29.3% and 61.2% higher, respectively, than those of the parent strain. These results indicated that in , Med15B regulates tolerance toward low pH via transcriptional regulation of acid stress response genes and alteration in lipid composition. This study explored the role of the Mediator tail subunit Med15B in the metabolism of under acidic conditions. Overexpression of enhanced yeast tolerance to low pH and improved biomass production, cell viability, and pyruvate yield. Membrane lipid composition data indicated that Med15B might play a critical role in membrane integrity, fluidity, and H-ATPase activity homeostasis at low pH. Thus, controlling membrane composition may serve to increase productivity at low pH.
是一种很有前景的有机酸生产者。为了阐明中介体尾部亚基Med15B在应对低pH胁迫中的生理功能，我们构建了一个缺失菌株Δ，以及一个过表达菌株Δ/。与亲本（Δ）菌株相比，在pH 2.0条件下，缺失导致生物量产量、葡萄糖消耗率和细胞活力分别下降了28.3%、31.7%和26.5%。在Δ菌株中，脂质代谢相关基因的表达显著下调，而麦角固醇生物合成的关键基因则出现异常上调。这导致C脂肪酸比例、不饱和脂肪酸与饱和脂肪酸之比（UFA/SFA）以及总磷脂含量分别下降了11.6%、27.4%和37.6%。细胞无法合成粪甾醇和麦角固醇，导致酵母甾醇积累，其浓度增加了60.3倍。此外，细胞的膜完整性、流动性和H - ATP酶活性分别降低了69.2%、11.6%和2l.8%。相比之下，Med15B的过表达使C水平、总磷脂、麦角固醇含量和UFA/SFA分别增加了18.6%、143.5%、94.5%和18.7%。膜完整性、流动性和H - ATP酶活性也分别增加了30.2%、6.9%和51.8%。此外,在没有pH缓冲的情况下，细胞干重和丙酮酸浓度分别比亲本菌株高29.3%和61.2%。这些结果表明，在中，Med15B通过对酸胁迫响应基因的转录调控和脂质组成的改变来调节对低pH的耐受性。本研究探讨了中介体尾部亚基Med15B在酸性条件下的代谢作用。的过表达增强了酵母对低pH的耐受性，提高了生物量产量、细胞活力和丙酮酸产量。膜脂质组成数据表明，Med15B可能在低pH条件下的膜完整性、流动性和H - ATP酶活性稳态中起关键作用。因此，控制膜组成可能有助于提高低pH条件下的生产力。
