在谷氨酸棒杆菌发酵产L-异亮氨酸的过程中,发酵后期菌体活力变弱,副产物增多,是限制L-异亮氨酸产业化的主要因素。研究通过3个阶段全营养流加策略探究最适发酵条件。首先,为解决L-异亮氨酸发酵中后期菌种活力下降的问题,实验通过利用发酵中后期全营养培养基流加策略,使得L-异亮氨酸达到了33.0 g/L。其次,为了解决初始发酵培养基高营养抑制问题,采用低浓度初始发酵培养基偶联发酵过程流加全营养控制策略,L-异亮氨酸达到了36.8 g/L。最后,由于玉米浆的高用量造成发酵染菌、起泡过多及后提取困难等产生的问题,通过清洁氮源丝肽粉等比例替换玉米浆全营养流加实验,使得副产物缬氨酸(valine,Val),亮氨酸(leucine,Leu),丙氨酸(alanine,Ala)分别降低到1.4、0.8、0.5 g/L,比初始降低了82.5%、86.7%和88.9%。通过上述3个阶段全营养流加策略,使得L-异亮氨酸产量提升的同时,副产物生成也得到有效的抑制。
During the fermentation process of L-isoleucine production by Corynebacterium glutamicum, the decrease of cell vitality and the increase of by-product in the last stages are the main factors limiting the industrialization of L-isoleucine production. Three-stage total nutrient fed-batch strategy was used to investigate optimal fermentation conditions. Firstly, to tackle the decrease in cell vitality in the mid-to-late stages of L-isoleucine fermentation, we adopted fed-batch method using complete medium with total nutrients, which resulted in an L-isoleucine concentration of 33.0 g/L. Secondly, to address the inhibition caused by high nutrient concentration at the initial stage of fermentation, we started with low-nutrient medium coupled with the total nutrient fed-batch method during the rest of the fermentation process, yielding an L-isoleucine concentration of 36.8 g/L. Finally, a high dose of corn steep liquor would create issues such as microbial contamination during fermentation, excessive foaming, and difficulty in the subsequent extraction. Therefore, we replaced corn steep liquor with silk peptide powder, which served as a clean nitrogen source. In this case, the concentrations of Val, Leu, and Ala by-products were reduced to 1.4, 0.8, and 0.5 g/L, respectively, which were 82.5%, 86.7%, and 88.9% lower than those of the original. Employing the above three-stage total nutrient fed-batch strategy increased the L-isoleucine yield, while effectively inhibiting the generation of by-products.
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