Techno-economical valorization of sugarcane bagasse for efficiently producing optically pure D-(−)-lactate approaching the theoretical maximum yield in low-cost salt medium by metabolically engineered Klebsiella oxytoca.

[Display omitted] • New study to expand the use of sugarcane bagasse (SCB) in the biorefinery concept. • Minimized cellulase at 15 U/g NaOH-pretreated SCB efficiently released sugars (70.8%). • K. oxytoca KIS004-91T produced D-lactate at 99.9 g/L with 0.97 g/g by fed-batch SSF. • D-lactate yield approached 97% theoretical maximum with 99.5% optical purity. Sugarcane bagasse (SCB) was utilized for efficiently producing optically pure D-(−)-lactate by Klebsiella oxytoca KIS004-91T strain. Cellulase (15 U/g NaOH-treated SCB) sufficiently liberated high sugars with saccharifications of 79.8 % cellulose and 52.5 % hemicellulose. For separated hydrolysis and fermentation, D-(−)-lactate was produced at 53.5 ± 2.1 g/L (0.98 ± 0.01 g/g sugar utilized or 0.71 ± 0.01 g/g total sugars) while D-(−)-lactate at 47.2 ± 1.8 g/L (0.78 ± 0.03 g/g sugar used or 0.69 ± 0.01 g/g total sugars) was obtained under simultaneous saccharification and fermentation (SSF). D-(−)-lactate at 99.9 ± 0.9 g/L (0.97 ± 0.01 g/g sugar utilized or 0.78 ± 0.01 g/g total sugars) was improved via fed-batch SSF. Based on mass balance, raw SCB of 7 kg is required to produce 1 kg D-(−)-lactate. Unlike others, D-(−)-lactate production was performed in low-cost salt medium without requirements of rich nutrients. Costs regarding medium, purification, and waste disposal may be reduced. This unlocks economic capability of SCB bioconversion or agricultural and agro-industrial wastes into high valuable D-(−)-lactate. [ABSTRACT FROM AUTHOR]