Preparation of High-Optical-Purity _L-Lactic Acid from _DL-Lactate using Optical Isomer Preferential Lactic Acid Assimilating Microorganisms

Abstract

　We have screened lactic acid assimilating microorganisms (LAAMs), which selectively assimilate either of the lactic acid optical isomers, to obtain l-lactic acid with high optical purity from dl-lactic acid. Eighty-nine strains of LAAMs were isolated from soil and plants. Six strains of LAAMs preferentially assimilate d-lactic acid on l-LAB medium, as evidenced by the increase in the ratio of l-lactic acid in culture broths. One such strain, LAAM055, prepared a high ratio of l-lactic acid (99.14%) and had high L-lactic acid yield (77.7%) ; this isolate may be suitable for the preparation of lactic acid with high optical purity. LAAM055 was identified as the ascomycetous anamorph yeast Geotrichum sp., with close relation to the species Geotrichum vulgare, as indicated by the morphological observations, physiological analysis, and sequence analysis of the 26S rDNA-D1/D2 region. Optimal temperature for d-lactic acid assimilation was 30℃, and optimal initial pH of the medium was 3.0. l-LAB medium prepared using GYP medium containing 2% glucose was more efficient for the production of lactic acid of high optical purity than that with 3% glucose. The most efficient initial inoculum concentration was obtained at OD _660nm 16.300.