Riboflavin overproduction from diverse feedstocks with engineered Corynebacterium glutamicum

Abstract

Abstract 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.