Metabolic Engineering Of Pediococcus Acidilactici With High Tolerance To Inhibitors For D-Lactic Acid Production Using Corn Stover Feedstock

Pediococcus acidilactici DQ2, isolated from the lignocellulose fermentation system, is a wild lactic acid-producing strain with high resistance. Based on simultaneous saccharification and fermentation (SSF), P. acidilactici DQ2 could ferment the dry dilute acid pretreated corn stover and produce high titer D/L-lactic acid at high solids loading. A genetically modified strain, P. acidilactici ZP26 was constructed by the disruption of the gene Idh encoding L-lactate dehydrogenase in P. acidilactici DQ2 by homologous recombination method using the thermosensitive suicide plamid pSET4E. P. acidilactici ZP26 produced optically pure D-lactic acid and the optical purity reached 99.32%using glucose as feedstock. It showed that the disruption of Idh had no influence on the cell growth, lactic acid yield and the tolerance to different inhibitors generated from the pretreatment of lignocellulose, while the glucose consumption and lactic acid productivity decreased.The simultaneous saccharification and lactic acid fermentation by P. acidilactici ZP26 was carried out using the pretreated and detoxified com stover as feedstock at 25%(w/w) solids loading. The study showed that inhibitor degradation and lactic acid accumulation were closely related to the detoxification time. Therefore the decerase of inhibitors in com stover was the important factor which leaded to the promoted lactic acid fermentation. Optically pure D-lactic acid with extremely high fermentation parameters was produced by P. acidilactici ZP26 using the com stover which detoxified for 10 days. And the D-lactic acid titer, productivity and yield reached 77.78 g L-1,1.02 g L-1 h-1, and 66.06%.This works is much important for the production of optically pure D-lactic acid using com stover.