Metabolic engineering for production of lactic acid and polylactic acid in Lactobacilli

Abstract

Arabic date, which is overproduced in Saudi Arabia, is mostly composed of sugars (70 ~ 80 wt%) that can be easily converted to lactic acid by lactic acid bacteria without complicated pretreatments. However, most studies on lactic acid fermentation from Arabic date juice have been limited to batch fermentation with medium optimization, and have not focused on industrially-relevant fed-batch process. In this study, we report the development of fed-batch fermentation process by using kinetic model for the efficient production of lactic acid to a high concentration from Arabic date juice. First, batch fermentation of Lactobacillus rhamnosus on Arabic date juice was conducted, and its kinetic model was built to quantita-tively understand the fermentation characteristics. Also, we developed a quick and simple method for building a kinetic model in EXCEL spread sheet which does not require com-plicate computational languages. This method can solve a series of differential equation, and find the best fitting parameter set in short time. Thanks to this method, the kinetic models of batch fermentation and fed-batch fermentations were built. Finally, the fed-batch kinetic model allows feed-forward control of substrate concentration during the feeding, which resulted in the production of 171 g/L of lactic acid with the productivity and yield of 1.58 g/L h and 87%, respectively. After building a robust lactic acid system, production of lactic acid containing polymer in Lactobacillus was carried out. Although the results are not clear and impressive, it is good enough to report that Lactobacillus has great potential for one-step PLA producing strain, and the following strategies are helpful on further improving.