State Key Laboratory of Biocatalysis and Enzyme Engineering, Environmental Microbial Technology Center of Hubei Province, College of Life Sciences, Hubei University, 368 Youyi Ave., Wuchang District, Wuhan, 430062, Hubei, China.
Hubei Provincial Center for Disease Control and Prevention, Wuhan, 430079, China.
Appl Microbiol Biotechnol. 2019 May;103(10):4003-4015. doi: 10.1007/s00253-019-09750-x. Epub 2019 Mar 28.
Poly-γ-glutamic acid (γ-PGA) is an extracellularly produced biodegradable polymer, which has been widely used as agricultural fertilizer, mineral fortifier, cosmetic moisturizer, and drug carrier. This study firstly discovered that lichenysin, as a biosurfactant, showed the capability to enhance γ-PGA production in Bacillus licheniformis. The exogenous addition of lichenysin improved the γ-PGA yield up to 17.9% and 21.9%, respectively, in the native strain B. licheniformis WX-02 and the lichenysin-deficient strain B. licheniformis WX02-ΔlchAC. The capability of intracellular biosynthesis of lichenysin was positively correlated with γ-PGA production. The yield of γ-PGA increased by 25.1% in the lichenysin-enhanced strain B. licheniformis WX02-Psrflch and decreased by 12.2% in the lichenysin-deficient strain WX02-ΔlchAC. Analysis of key enzyme activities and gene expression in the TCA cycle, precursor glutamate synthesis, and γ-PGA synthesis pathway revealed that the existence of lichenysin led to increased γ-PGA via shifting the carbon flux in the TCA cycle towards glutamate and γ-PGA biosynthetic pathways, minimizing by-product formation, and facilitating the uptake of extracellular substrates and the polymerization of glutamate to γ-PGA. Insight into the mechanisms of enhanced production of γ-PGA by lichenysin would define the essential parameters involved in γ-PGA biosynthesis and provide the basis for large-scale production of γ-PGA.
聚-γ-谷氨酸（γ-PGA）是一种可生物降解的胞外聚合物，已广泛用作农业肥料、矿物质强化剂、化妆品保湿剂和药物载体。本研究首次发现，岩大戟内酯作为一种生物表面活性剂，具有增强地衣芽孢杆菌中γ-PGA 生产的能力。外源添加岩大戟内酯分别将天然菌株 B. licheniformis WX-02 和岩大戟内酯缺陷菌株 B. licheniformis WX02-ΔlchAC 的 γ-PGA 产量提高了 17.9%和 21.9%。岩大戟内酯的细胞内生物合成能力与 γ-PGA 生产呈正相关。岩大戟内酯增强菌株 B. licheniformis WX02-Psrflch 的 γ-PGA 产量增加了 25.1%，而岩大戟内酯缺陷菌株 WX02-ΔlchAC 的产量则降低了 12.2%。对 TCA 循环、前体谷氨酸合成和 γ-PGA 合成途径中的关键酶活性和基因表达的分析表明，岩大戟内酯的存在通过将 TCA 循环中的碳通量转向谷氨酸和 γ-PGA 合成途径，最大限度地减少副产物的形成，促进细胞外底物的摄取和谷氨酸向 γ-PGA 的聚合，从而导致 γ-PGA 产量增加。深入了解岩大戟内酯增强 γ-PGA 生产的机制，将确定 γ-PGA 生物合成中涉及的基本参数，并为 γ-PGA 的大规模生产提供基础。
