(448a) A Potential Sporolactobacillus Strian and Its Enhanced Production of an Optically Purified D-Lactic Acid for the Stereocomplex Polylactic Acid
Plastics that are widely used nowadays are from petroleum based resources. The petroleum based plastics are generally classified as non compostable or partial compostable with the help of some additives added while processing into the plastic products. Due to a large plastic consumption and a long term degradation profile, this eventually leads to the environmental pollution. As a result, research on the compostable plastic has become of interest. Polylactic acid (PLA) is a good example of compostable plastic made from the renewable resources such as plant biomass and agricultural commodities. During the initial phase of development, PLA was made from polymerization of the optically pure L-lactic acid since the L-form can be easily found in nature and has long been extensively used in food and pharmaceutical industries. Nonetheless, poly L-lactic acid (PLLA) still cannot be competitive with the petroleum based plastics due to the poor mechanical and thermal properties causing several problems in compounding and fabrication. The deficiency in such properties can be reduced by the stereocomplex structure of PLA. This structure can be tailored made by polymerizing the optically pure L-lactic acid with the optically pure D-lactic acid which is rarely found in nature due to its non – biocompatible property. Nevertheless, some bacteria can produce this stereoisomer of lactic acid as the protecting agent under stress conditions. We have isolated and screened the D-lactate producers from the natural resources and later identified as Sporolactobacillus laevolacticus SK5-2. Extensive fermentation optimization was conducted in a 5 L stirred fermentor. Compared to those commercial strains available, our SK5-2 gave the very high D-lactate yield of 0.92 g per g glucose and productivity of 3.83 g/L×h with the final titer of 115 g/L and the optical purity of 99.0% ee from the simple medium containing the initial glucose of 120 g/L.