Production of optically pure l-lactic acid from lignocellulosic hydrolysate by using a newly isolated and d-lactate dehydrogenase gene-deficient Lactobacillus paracasei strain

• L. paracasei 7B could produce lactic acid with excellent production efficiency.
• L. paracasei 7B could tolerate to inhibitors produced from pretreated lignocellulose.
• ldhD deficient strain 7BL could produce optically pure l-lactic acid.
• L. paracasei 7BL could produce l-lactic acid from lignocellulosic hydrolysate.
• L. paracasei 7BL represents a potential for large-scale industrial application.

The use of lignocellulosic feedstock for lactic acid production with a difficulty is that the release of inhibitory compounds during the pretreatment process which inhibit the growth of microorganism. Thus we report a novel lactic acid bacterium, Lactobacillus paracasei 7BL, that has a high tolerance to inhibitors and produced optically pure l-lactic acid after the interruption of ldhD gene. The strain 7BL fermented glucose efficiently and showed high titer of l-lactic acid (215 g/l) by fed-batch strategy. In addition, 99 g/l of l-lactic acid with high yield (0.96 g/g) and productivity (2.25–3.23 g/l/h) was obtained by using non-detoxified wood hydrolysate. Rice straw hydrolysate without detoxification was also tested and yielded a productivity rate as high as 5.27 g/l/h. Therefore, L. paracasei 7BL represents a potential method of l-lactic acid production from lignocellulosic biomass and has attractive application for industries.