Abstract：
Riboflavin overproduction byCorynebacterium glutamicumwas achieved by screening synthetic operons, enabling fine-tuned expression of the riboflavin biosynthetic genesribGCAH.The synthetic operons were designed by means of predicted translational initiation rates of each open reading frame, with the best-performing selection enabling riboflavin overproduction without negatively affecting cell growth. Overexpression of the fructose-1,6-bisphosphatase (fbp) and 5-phosphoribosyl 1-pyrophosphate aminotransferase (purF) encoding genes was then done to redirect the metabolic flux towards the riboflavin precursors. The resulting strain produced 8.3 g l-1of riboflavin in glucose-based fed-batch fermentations, which is the highest reported riboflavin titer withC. glutamicum. Further genetic engineering enabled both xylose and mannitol utilization byC. glutamicum, and we demonstrated riboflavin overproduction with the xylose-rich feedstocks rice husk hydrolysate and spent sulfite liquor, and the mannitol-rich feedstock brown seaweed hydrolysate. Remarkably, rice husk hydrolysate provided 30% higher riboflavin yields compared to glucose in the bioreactors.
摘要：
谷氨酸棒杆菌核黄素的过量生产是通过筛选合成操纵子实现的，能够微调核黄素生物合成基因ribGCAH的表达。通过预测每个开放阅读框的翻译起始速率来设计合成操纵子，具有最佳性能的选择，使核黄素过度生产，而不会对细胞生长产生负面影响。然后进行果糖-1,6-双磷酸酶（fbp）和5-磷酸核糖1-焦磷酸氨基转移酶（purF）编码基因的过表达，以将代谢通量重定向到核黄素前体。所得菌株在基于葡萄糖的分批补料发酵中产生8.3g/L的核黄素，这是报道的最高的核黄素滴度与谷氨酸棒杆菌。进一步的基因工程使谷氨酸棒杆菌能够利用木糖和甘露醇，我们证明了富含木糖的原料稻壳水解物和亚硫酸盐废液中核黄素的过量生产，和富含甘露醇的原料褐藻水解物。值得注意的是,与生物反应器中的葡萄糖相比，稻壳水解产物的核黄素产量高30％。
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