Tuesday, May 3, 2011
Lactic acid is a platform chemical for production of polylactic acid (PLA) polymer, which as sustainable replacement to petroleum-based polymer like plastic and fiber. We have been developed a free D-(-)-lactic acid producing Zymomonas mobilis strain by introducing a heterologous D-lactate dehydrogenase (D-ldh) gene. It showed that D-(-)-lactic acid was produced close to the theoretical yield (almost 1.0 g lactic acid g-1 glucose) either under non-buffered condition of pH 3.0 (without pH control) or buffered condition of pH 5.0. The optical purity of D-(-)-lactic acid was extremely high of 99.9% or above in all conditions. The highest yield was reached to 99% with amount of 35.0 g l-1 D-(-)-lactic acid; meanwhile the productivity was slightly low within 1.5 g l-1 h-1. Moreover, non-buffered cultures were conducted to further purifications to develop a possible process for the production of free lactic acid and optically pure D-(-)-lactic acid. These are strongly expected to be a microbial alternative bringing the economic free D-(-)-lactic acid production from biomass.