Xylonic Acid Production from Sugarcane Bagasse Hydrolysate Using an Engineered Komagataella phaffii Strain

Xylonic acid is an oxidized derivative of xylose that is used by the food, pharmaceutical, and chemical industries. It can be produced either microbially or chemically. Biological production is advantageous because of its safety, eco-friendliness, and mild process conditions. This study used a recombinant Komagataella phaffii strain modified to produce xylonic acid from xylose. Glucose and glycerol were evaluated as co-substrates in batch and fed-batch fermentations in flasks and in bioreactor cultures. Glycerol was an effective carbon source for improving growth and product production. Batch fermentations with glycerol produced 24.88 ± 1.64 g.L^-1 of xylonic acid, with a yield of 0.55 ± 0.03 g_{xylonic acid}.g_xylose^-1 and a productivity of 0.26 ± 0.02 g_{xylonic acid}.L^-1.h^-1, while those with glucose yielded 20.30 ± 0.31 g.L^-1, with a conversion factor of 0.50 ± 0.01 g_{xylonic acid}.g_xylose^-1 and a productivity of 0.21 g_{xylonic acid}.L^-1.h^-1. Further, flask fermentations were run where glucose or glycerol was pulse fed. Glycerol-fed cultures produced 20.87 ± 0.30 g.L^-1 of xylonic acid, with a productivity of 0.11 g_{xylonic acid}.L^-1.h^-1. Xylonic production was further improved in computer-controlled bioreactor cultures. Pulse batch fermentation (240 h, pH 5.5, 0.8 L.min^-1 airflow) achieved a xylonic acid titer of 55.11 ± 2.36 g.L^-1 with a productivity of 0.19 ± 0.01 g_{xylonic acid}.L^-1.h^-1. Finally, xylonic acid was produced from xylose using hydrolysate produced from sugarcane bagasse. The final concentration and productivity were 42.30 g.L^-1 of xylonic acid and 0.44 g.L^-1.h^-1, respectively.