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.