Riboflavin overproduction from diverse feedstocks with engineered Corynebacterium glutamicum .

Riboflavin overproduction by Corynebacterium glutamicum was achieved by screening synthetic operons, enabling fine-tuned expression of the riboflavin biosynthetic genes ribGCAH. 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 ^-1 of riboflavin in glucose-based fed-batch fermentations, which is the highest reported riboflavin titer with C. glutamicum . Further genetic engineering enabled both xylose and mannitol utilization by C. 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.
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