Highly efficient production of l-lactic acid from xylose by newly isolated Bacillus coagulans C106

Cost-effective production of optically pure lactic acid from lignocellulose sugars is commercially attractive but challenging. Bacillus coagulans C106 was isolated from environment and used to produce l-lactic acid from xylose at 50 °C and pH 6.0 in mineral salts medium containing 1–2% (w/v) of yeast extract without sterilizing the medium before fermentation. In batch fermentation with 85 g/L of xylose, lactic acid titer and productivity reached 83.6 g/L and 7.5 g/L h, respectively. When fed-batch (120 + 80 + 60 g/L) fermentation was applied, they reached 215.7 g/L and 4.0 g/L h, respectively. In both cases, the lactic acid yield and optical purity reached 95% and 99.6%, respectively. The lactic acid titer and productivity on xylose are the highest among those ever reported. Ca(OH)2 was found to be a better neutralizing agent than NaOH in terms of its giving higher lactic acid titer (1.2-fold) and productivity (1.8-fold) under the same conditions.