Department of Chemical and Biological Engineering, Korea University, 145 Anam-ro, Seongbuk-gu, Seoul, 02841, South Korea.
Department of Chemical Engineering, Pohang University of Science and Technology, 77 Cheongam-ro, Nam-gu, Pohang, Gyeongbuk, 37673, South Korea.
Microb Cell Fact. 2019 Oct 10;18(1):170. doi: 10.1186/s12934-019-1224-8.
Most microorganisms have evolved to maximize growth rate, with rapid consumption of carbon sources from the surroundings. However, fast growing phenotypes usually feature secretion of organic compounds. For example, E. coli mainly produced acetate in fast growing condition such as glucose rich and aerobic condition, which is troublesome for metabolic engineering because acetate causes acidification of surroundings, growth inhibition and decline of production yield. The overflow metabolism can be alleviated by reducing glucose uptake rate.
As glucose transporters or their subunits were knocked out in E. coli, the growth and glucose uptake rates decreased and biomass yield was improved. Alteration of intracellular metabolism caused by the mutations was investigated with transcriptome analysis and C metabolic flux analysis (C MFA). Various transcriptional and metabolic perturbations were identified in the sugar transporter mutants. Transcription of genes related to glycolysis, chemotaxis, and flagella synthesis was downregulated, and that of gluconeogenesis, Krebs cycle, alternative transporters, quorum sensing, and stress induced proteins was upregulated in the sugar transporter mutants. The specific production yields of value-added compounds (enhanced green fluorescent protein, γ-aminobutyrate, lycopene) were improved significantly in the sugar transporter mutants.
The elimination of sugar transporter resulted in alteration of global gene expression and redirection of carbon flux distribution, which was purposed to increase energy yield and recycle carbon sources. When the pathways for several valuable compounds were introduced to mutant strains, specific yield of them were highly improved. These results showed that controlling the sugar uptake rate is a good strategy for ameliorating metabolite production.
大多数微生物已经进化到最大限度地提高增长率，快速消耗周围的碳源。然而，快速生长的表型通常伴随着有机化合物的分泌。例如，大肠杆菌主要在富含葡萄糖和需氧条件下产生乙酸盐，这对代谢工程来说很麻烦，因为乙酸盐会导致周围环境酸化、生长抑制和产物产量下降。通过降低葡萄糖摄取率可以缓解这种溢出代谢。
当大肠杆菌中的葡萄糖转运蛋白或其亚基被敲除时，生长和葡萄糖摄取率降低，生物量产量提高。通过转录组分析和 C 代谢通量分析 (C MFA) 研究了突变引起的细胞内代谢变化。在糖转运突变体中鉴定出各种转录和代谢扰动。糖酵解、趋化作用和鞭毛合成相关基因的转录下调，而糖异生、克雷布斯循环、替代转运蛋白、群体感应和应激诱导蛋白的转录上调。在糖转运突变体中，有价值化合物（增强型绿色荧光蛋白、γ-氨基丁酸、番茄红素）的特定生产产量显著提高。
糖转运蛋白的消除导致了全局基因表达的改变和碳通量分布的重定向，这旨在提高能量产量并回收碳源。当将几种有价值化合物的途径引入突变株时，它们的特定产量得到了极大的提高。这些结果表明，控制糖摄取率是改善代谢产物生产的一种好策略。
