利用甜菜碱提升赖氨酸发酵及其代谢通量分析

The effect of betaine on lysine production and the corresponding metabolic flux analysis

赖氨酸发酵后期会产生很高的渗透压。甜菜碱可以有效提高大肠杆菌对渗透压的耐受性,大肠杆菌菌体自身对渗透压的耐受机制反而会受其抑制。激活菌体自身的渗透压耐受机制,可以提高发酵指标。实验结果表明:在菌体生长到OD562为19.5后添加甜菜碱,可以使赖氨酸的发酵强度从5.6 g/(L·h)提升至6.3 g/(L·h),转化率从65%提升至68.5%。提高初糖质量浓度也能激活菌体渗透压耐受性,可以进一步提高发酵强度至6.6 g/(L·h)。代谢通量分析结果表明:高转化率工艺条件下6-磷酸果糖的逆向转化进入磷酸戊糖途径的通量较对照提高43%,而TCA循环通量较对照降低18.6%。研究结果表明:除去发酵初期的甜菜碱并提高初糖质量浓度有利于提高赖氨酸发酵水平,要提高转化率需将更多6-磷酸果糖导入磷酸戊糖途径并降低TCA循环通量。

The osmotic pressure is very high at the end of the lysine fermentation process.Betaine is usually used as osmolyte to relieve the impact of the high osmotic pressure. However, the addition of betaine can inhibit the inner tolerance of E. coli to high osmotic pressure. In order to improve the titer of lysine fermentation, its inner tolerance against osmotic pressure should be activated. When betaine was added at OD 562 of 19.5, the productivity increased from 5.6 g/(L·h) to 6.3 g/(L·h), and yield increased from 65% to 68.5%. The increase of initial glucose concentration can also promote the productivity to 6.6 g/(L·h). The combination of inner tolerance and addition of osmolyte can further relieve higher osmotic pressure at the end of the fermentation process than the addition of osmolyte alone. The metabolic flux of high lysine yield process was analyzed. The flux of the reverse conversion of fructose-6P was 43% higher than the control and TCA cycle flux was 18.6% lower than the control. These results indicated that the removal of betaine from the initial medium and the increase of initial glucose concentration are beneficial to lysine fermentation.