Sequential coupling of enzymatic hydrolysis and fermentation platform for high yield and economical production of 2,3-butanediol from cassava by metabolically engineered Klebsiella oxytoca

BACKGROUND 2,3-butanediol (2,3-BD) is one of the important platform chemicals used for biofuels and biochemicals. To make an economically feasible production of 2,3-BD, an optimization process with a cheap substrate is required. The best conditions for enzymatic hydrolysis and fermentation were investigated to achieve high concentration and yield of 2,3-BD from cassava starch while reducing the production cost regarding enzyme usage, energy input and medium preparation. RESULTS A 2.5 L bioreactor containing 1 L working volume of sterilized and gelatinized starch (130 g L-1) was placed at room temperature (25 degrees C). When the temperature of the starch solution reached 85 degrees C, alpha-amylase (200 U g(-1) starch) was added to the solution. The enzymatic reaction was allowed to proceed while the temperature of the solution was simultaneously dampened to 45 degrees C within 1 h. The reaction was further maintained at 45 degrees C for another 2 h. After hydrolysis, 64.8 g L-1 2,3-BD was produced with a yield of 0.46 g g(-1), productivity of 1.25 g L-1 h(-1) and few by-products by Klebsiella oxytoca KMS006. Further improvements of 2,3-BD (92.5 g L-1) and yield (0.49 g g(-1)) were observed in fed-batch mode under a constant feeding rate of 3.5 g starch h(-1). CONCLUSION With our developed strategy, costs related to energy consumption and medium preparation were reduced by using heat generated by autoclave as well as by neglecting the use of glucoamylase for hydrolysis of cassava starch. The highest yield of 2,3-BD (0.49 g g(-1)) was achieved, which is 98% of theoretical maximum. The process may be applied to the economical production of 2,3-BD. (c) 2020 Society of Chemical Industry