Institute of Microbiology and Biotechnology, University of Latvia, Kronvalda Boulevard 4, 1586 Riga, Latvia.
J Ind Microbiol Biotechnol. 2010 Jul;37(7):689-99. doi: 10.1007/s10295-010-0712-y. Epub 2010 Apr 4.
Cell growth limitation is known to be an important condition that enhances L: -valine synthesis in Corynebacterium glutamicum recombinant strains with L: -isoleucine auxotrophy. To identify whether it is the limited availability of L: -isoleucine itself or the L: -isoleucine limitation-induced rel-dependent ppGpp-mediated stringent response that is essential for the enhancement of L: -valine synthesis in growth-limited C. glutamicum cells, we deleted the rel gene, thereby constructing a relaxed (rel (-) ) C. glutamicum DeltailvA DeltapanB Deltarel ilvNM13 (pECKAilvBNC) strain. Variations in enzyme activity and L: -valine synthesis in rel (+) and rel (-) strains under conditions of L: -isoleucine excess and limitation were investigated. A sharp increase in acetohydroxy acid synthase (AHAS) activity, a slight increase in acetohydroxyacid isomeroreductase (AHAIR) activity, and a dramatic increase in L: -valine synthesis were observed in both rel (+) and rel (-) cells exposed to L: -isoleucine limitation. Although the positive effect of induction of the stringent response on AHAS and AHAIR upregulation in cells was not confirmed, we found the stringent response to be beneficial for maintaining increased AHAS, dihydroxyacid dehydratase, and transaminase B activity and L: -valine synthesis in cells during the stationary growth phase.
细胞生长限制被认为是增强具有 L：-异亮氨酸营养缺陷的谷氨酸棒杆菌重组菌株中 L：-缬氨酸合成的重要条件。为了确定增强生长受限的谷氨酸棒杆菌细胞中 L：-缬氨酸合成所必需的是 L：-异亮氨酸本身的有限可用性还是 L：-异亮氨酸限制诱导的 rel 依赖性 ppGpp 介导的严格反应，我们删除了 rel 基因，从而构建了松弛（rel（-））谷氨酸棒杆菌 DeltailvA DeltapanB Deltarel ilvNM13（pECKAilvBNC）菌株。在 L：-异亮氨酸过量和限制条件下，研究了 rel（+）和 rel（-）菌株中酶活性和 L：-缬氨酸合成的变化。在暴露于 L：-异亮氨酸限制的 rel（+）和 rel（-）细胞中，均观察到乙酰羟酸合酶（AHAS）活性急剧增加，乙酰羟酸异构还原酶（AHAIR）活性略有增加，L：-缬氨酸合成显著增加。尽管没有证实严格反应对 AHAS 和 AHAIR 上调的诱导有积极作用，但我们发现严格反应有利于在静止生长阶段维持增加的 AHAS、二羟酸脱水酶和转氨酶 B 活性和 L：-缬氨酸合成。
