He Xun, Chen Kequan, Li Yan, Wang Zhen, Zhang Hong, Qian Juan, Ouyang Pingkai
State Key Laboratory of Materials-Oriented Chemical Engineering, College of Biotechnology and Pharmaceutical, Nanjing Tech University, Nanjing, 211816, People's Republic of China.
Bioprocess Biosyst Eng. 2015 Aug;38(8):1615-22. doi: 10.1007/s00449-015-1403-x. Epub 2015 Apr 22.
Faster sugar consumption rate and low-cost nitrogen source are required for the chemical biosynthesis using molasses. Five pretreatment methods were applied to beet molasses prior to fermentation through engineered Escherichia coli, respectively, and corn steep liquid was used as an organic nitrogen source to replace expensive yeast extract. Furthermore, the effects of different feeding strategy in fed-batch fermentation on L-lysine production were investigated. The experimental results showed that combined tricalcium phosphate, sulfuric acid, and activated carbon pretreatment method (TPSA) pretreatment could improve the sugar consumption rate most greatly, and the initial total sugar concentration of 35 g/L from TPSA-pretreated beet molasses gave the best results with respect to L-lysine production, dry cell weight concentration, and L-lysine yield in batch fermentation. Moreover, a mixture of low-cost corn steep liquid and yeast extract containing equal amount of nitrogen could be used as the organic nitrogen source for effective L-lysine fermentation, and constant speed feeding strategy of TPSA-pretreated beet molasses promoted L-lysine production by engineered E. coli. The TPSA-pretreated beet molasses had a sugar consumption rate of 1.75 g/(L h), and a L-lysine yield of 27.81% was achieved, compared with the theoretical yield of 62% by glucose. It was clarified that the pretreatment significantly enhanced the conversion of sugars in beet molasses to L-lysine.
使用糖蜜进行化学生物合成需要更快的糖消耗速率和低成本的氮源。在通过工程化大肠杆菌进行发酵之前，分别对甜菜糖蜜应用了五种预处理方法，并使用玉米浆作为有机氮源来替代昂贵的酵母提取物。此外，还研究了分批补料发酵中不同补料策略对L-赖氨酸生产的影响。实验结果表明，磷酸三钙、硫酸和活性炭联合预处理方法（TPSA）预处理能最大程度地提高糖消耗速率，TPSA预处理的甜菜糖蜜初始总糖浓度为35 g/L时，在分批发酵中L-赖氨酸产量、干细胞重量浓度和L-赖氨酸产率方面取得了最佳结果。此外，含有等量氮的低成本玉米浆和酵母提取物的混合物可作为有效L-赖氨酸发酵的有机氮源，TPSA预处理的甜菜糖蜜的恒速补料策略促进了工程化大肠杆菌生产L-赖氨酸。TPSA预处理的甜菜糖蜜的糖消耗速率为1.75 g/(L·h)，L-赖氨酸产率达到27.81%，而葡萄糖的理论产率为62%。结果表明，预处理显著提高了甜菜糖蜜中糖向L-赖氨酸的转化。
