溶氧强制振荡对L-苏氨酸发酵产率及其代谢流迁移的影响

为有效降低L-苏氨酸发酵过程中副产物的积累,考察了发酵过程中的溶氧强制振荡对L-苏氨酸发酵产率及其多种副产物积累的影响,并深入探讨了振荡行为对L-苏氨酸生物合成代谢网络的代谢流分布的影响。结果表明:采用溶氧强制振荡工艺能够明显提高L-苏氨酸的发酵产率和降低多种抑制性产物的合成。与非振荡工艺相比,经过36h培养,细胞生物量达到29.5g·L-1,苏氨酸的质量浓度达到118.9g·L-1,而乙酸质量浓度下降到0.8g·L-1,副产的其他氨基酸也大大降低。通过代谢流分析表明,在发酵后期的一个振荡周期(30h至31h)内,与非振荡组相比,HMP途径的代谢流量由6.5提高至95.88,CO2固定反应代谢流量由45.1提高至86.1,TCA循环相对代谢流量从1.86提高至17.78,从而导致苏氨酸对葡萄糖的质量转化率从30.0%增加至57.0%。溶氧强制振荡条件下的苏氨酸发酵液中各种副产物更少,更适合今后的大规模工业化生产。

Effects of Dissolved Oxygen Forced Oscillation on the Biosynthesis of L-Threonine and Shift of Metabolic Flux in Escherichia Coli TRFC

In order to reduce the accumulation of byproducts significantly, the dissolved oxygen (DO) forced oscillation was designed and evaluated for enhancing biosynthesis of L-threonine with recombinant E.coli TRFC. The results show that this new DO control mode could improve the productivity of L-threonine and reduce the accumulation of the byproducts greatly. With this DO oscillation mode, the cell density and L-threonine concentration are improved up to 29.5 g·L~(-1) and 118.9 g·L~(-1), respectively; whereas, the acetate concentration is reduced to 0.8 g·L~(-1). Further analysis of metabolic flux distribution shows that, compared with the non-DO control mode, the carbon flux to HMP (Hexose Monophosphate Pathway) is increased from 6.5 to 95.88, the anaplerotic reaction from 45.1 to 86.1 and the TCA(Tricar boxylic acid) cycle relative flux from 1.86 to 17.78 during the oscillation period from 30 h to 31 h. The shift of these metabolic fluxes leads to the obvious increase of the glucose-to-L-threonine conversion ratio from 30.0% to 57.0%. Further analyses of both DO controlled and non-controlled fermentation broths show that the concentrations of different byproducts are greatly reduced with the dissolved oxygen forced oscillation. The present work is very helpful to improve the commercial production of L-threonine in the future.