Lactic acid (LA) and its derivatives are versatile chemicals used in food, pharmaceutical, leather, and polylactic acid (PLA) plastics industries. A homolactic fermenter, Lactobacillus pentosus 124-2, was used to produce lactic acid by our laboratory. For reducing the cost of purification L-(+) and D-(-) lactic acid isomers respectively, three approaches have being used in this study. The first, a regenerated resource, the wastewater sludge from a paper-manufacturer , was used as the only carbon source. After growing for 48 hours, 1.01 g/L of lactate could be retrieved from a 100 ml-batch culture. The second, L. pentosus was co-cultured with two water rating bacteria (Clostridium M1 and Bacillus I) to improve the converting efficiency of biomass in sludge. When L. pentosus was co-cultured with Clostridium M1, the production of lactic acid was increased to 1.35(g/L) after a growth of 34 hours and existed only as L-(+) isomer (0.56 g/L) after 108 hours. If L. pentosus was co-cultured with Clostridium M1 and Bacillus I simultaneously, still only L-(+) isomer, but a little more (0.837 g/L), could be detected after growing for 155 hours. The third, a molecular biological approach was used to knock out the L-lactate dehydrogenase (LDH) gene and D-lactate dehydrogenase (LDH) gene of L. pentosus, so that the resulting mutants will produce L-(+) and D-(-) isomers, respectively. Six recombinant plasmids have been constructed and some other works are in progress.

polylactic acid ,wastewater