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  • Title: [γ-Polyglutamic acid production in Corynebacterium glutamicum using sugar by one-step fermentation].
    Author: Cheng H, Chen Y, Zhu Y, Cao R, Xu G, Zhang X, Shi J, Xu Z.
    Journal: Sheng Wu Gong Cheng Xue Bao; 2020 Feb 25; 36(2):295-308. PubMed ID: 32148002.
    Abstract:
    γ-polyglutamic acid (γ-PGA) is widely used in food processing, cosmetic production, medicinal industry, etc. Currently, the production strains used in fermentation process are commonly glutamic acid-dependent, which results in extra cost. In this study, a de novo way of producing γ-PGA from sugars was reported. To this end, the γ-polyglutamate synthase gene cluster pgsBCA was cloned from the natural γ-PGA-producing strain Bacillus subtilis (ATCC 6051-U), and was constitutively and inducibly expressed in Corynebacterium glutamicum ATCC 13032. Only inducible expression of pgsBCA can lead to the generation of γ-PGA with a titer of 1.43 g/L from glucose, without any supplementation of glutamic acid. The production was further elevated to 1.98 g/L upon optimization of the induction conditions with the induction time at 2 h post-inoculation and the IPTG concentration of 0.8 mmol/L. Moreover, to achieve a higher titer of γ-PGA, pgsBCA was inducibly expressed in C. glutamicum F343, which shows a paramount glutamate production capacity. The final γ-PGA production reached 10.23 g/L in shake flasks and 20.08 g/L in a 5-L fermentor using glucose as the substrate. The weight-average molecular weight (Mw) of γ-PGA from recombinant strain F343 showed 34.77% higher than that produced by B. subtilis. This study provides a novel way of producing γ-PGA from sugars directly and potentiates new applications of γ-PGA in the future. γ-聚谷氨酸在食品、化妆品、生物医药等领域具有广泛的应用,目前主要的生产菌株是谷氨酸依赖型菌株,在生产过程中需要添加谷氨酸作为前体,因而生产γ-聚谷氨酸的成本较高。文中主要研究从糖质原料一步法发酵合成γ-聚谷氨酸的生产工艺。首先,从产γ-聚谷氨酸的菌株枯草芽孢杆菌中克隆γ-聚谷氨酸合成酶的基因簇pgsBCA,在谷氨酸棒杆菌模式菌株ATCC13032 中进行诱导型和组成型表达,结果显示,仅诱导型表达菌株可以积累γ-聚谷氨酸,产量为1.43 g/L。进一步对诱导条件进行优化,确定诱导时间为2 h,IPTG 浓度为0.8 mmol/L,γ-聚谷氨酸产量为1.98 g/L。在此基础上,在一株高产谷氨酸的谷氨酸棒杆菌F343 中外源表达pgsBCA,对重组菌进行发酵,结果表明,在摇瓶发酵中γ-聚谷氨酸产量达到10.23 g/L,在5 L 发酵罐中产量达到20.08 g/L;继而对γ-聚谷氨酸进行分子量测定,结果显示,产自F343 重组菌的γ-聚谷氨酸的重均分子量比产自枯草芽孢杆菌的提高34.77%。文中构建了一步法发酵糖质原料生产γ-聚谷氨酸的新途径,同时为开发其潜在应用奠定了基础。.
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