Production of d-lactate from sugarcane bagasse and corn stover hydrolysates using metabolic engineered Escherichia coli strains

In this study, the lactogenic Escherichia coli strain JU15 was used and modified to produce d-lactate (d-LA) from plant hydrolysates with a minimal nutrient addition in pH controlled fermenters. Results showed that strain JU15 produces d-LA with high yield and productivity in laboratory simulated hydrolysate media and actual sugar cane bagasse hemicellulosic hydrolysate. Strain JU15 showed sequential carbon source utilization and acetic acid production. The l-lactic and acetic acid production pathways were deleted in JU15, resulting strain AV03 (JU15 ΔpoxB, ΔackA-pta, ΔmgsA), which showed simultaneous consumption of glucose and xylose and no acetic acid production in the simulated hydrolysate. The d-LA yield from hydrolysate sugars was close to 0.95 gD-LA/gsugars in all cases. Our results show that d-LA can be produced from plant hydrolysates in simple batch fermentation processes with a high productivity using engineered E. coli strains at fermenter scales from 0.2 up to 10 L.