Ju Si Yeon, Kim Jin Ho, Lee Pyung Cheon
Department of Molecular Science and Technology, Ajou University, Woncheon-dong, Yeongtong-gu, Suwon, 443-749 South Korea.
Department of Applied Chemistry and Biological Engineering, Ajou University, Woncheon-dong, Yeongtong-gu, Suwon, 443-749 South Korea.
Biotechnol Biofuels. 2016 Nov 9;9:240. doi: 10.1186/s13068-016-0662-3. eCollection 2016.
Lactic acid has been approved by the United States Food and Drug Administration as Generally Regarded As Safe (GRAS) and is commonly used in the cosmetics, pharmaceutical, and food industries. Applications of lactic acid have also emerged in the plastics industry. Lactic acid bacteria (LAB), such as and , are widely used as lactic acid producers for food-related and biotechnological applications. Nonetheless, industrial mass production of lactic acid in LAB is a challenge mainly because of growth inhibition caused by the end product, lactic acid. Thus, it is important to improve acid tolerance of LAB to achieve balanced cell growth and a high titer of lactic acid. Recently, adaptive evolution has been employed as one of the strategies to improve the fitness and to induce adaptive changes in bacteria under specific growth conditions, such as acid stress.
Wild-type was challenged long term with exogenously supplied lactic acid, whose concentration was increased stepwise (for enhancement of lactic acid tolerance) during 1 year. In the course of the adaptive evolution at 70 g/L lactic acid, three mutants (LMS50, LMS60, and LMS70) showing high specific growth rates and lactic acid production were isolated and characterized. Mutant LMS70, isolated at 70 g/L lactic acid, increased d-lactic acid production up to 76.8 g/L, which was twice that in the wild type (37.8 g/L). Proteomic, genomic, and physiological analyses revealed that several possible factors affected acid tolerance, among which a mutation of ATPase ε subunit (involved in the regulation of intracellular pH) and upregulation of intracellular ammonia, as a buffering system, were confirmed to contribute to the observed enhancement of tolerance and production of d-lactic acid.
During adaptive evolution under lethal stress conditions, the fitness of gradually increased to accumulate beneficial mutations according to the stress level. The enhancement of acid tolerance in the mutants contributed to increased production of d-lactic acid. The observed genetic and physiological changes may systemically help remove protons and retain viability at high lactic acid concentrations.
乳酸已被美国食品药品监督管理局批准为一般认为安全（GRAS）物质，常用于化妆品、制药和食品工业。乳酸在塑料工业中的应用也已出现。乳酸菌（LAB），如[具体菌种1]和[具体菌种2]，被广泛用作食品相关和生物技术应用中的乳酸生产者。然而，LAB中乳酸的工业大规模生产面临挑战，主要原因是终产物乳酸会抑制生长。因此，提高LAB的耐酸性对于实现细胞的平衡生长和高乳酸产量至关重要。最近，适应性进化已被用作一种策略，以提高细菌在特定生长条件下（如酸胁迫）的适应性并诱导适应性变化。
野生型[具体菌种]长期受到外源供应乳酸的挑战，在1年时间里乳酸浓度逐步增加（以提高耐乳酸能力）。在70 g/L乳酸的适应性进化过程中，分离并鉴定了三个表现出高比生长速率和乳酸产量的突变体（LMS50、LMS60和LMS70）。在70 g/L乳酸下分离得到的突变体LMS70，d-乳酸产量增加至76.8 g/L，是野生型（37.8 g/L）的两倍。蛋白质组学、基因组学和生理学分析表明，有几个可能的因素影响耐酸性，其中ATP酶ε亚基的突变（参与细胞内pH调节）和作为缓冲系统的细胞内氨的上调被证实有助于观察到的耐酸性增强和d-乳酸的产生。
在致死胁迫条件下的适应性进化过程中，[具体菌种]的适应性根据胁迫水平逐渐提高，以积累有益突变。突变体耐酸性的增强有助于d-乳酸产量的增加。观察到的遗传和生理变化可能有助于系统地去除质子并在高乳酸浓度下保持活力。
Zotero 插件
