Evaluation of fresh water lactic acid bacteria for production of optically pure L-(+)-lactic acid

Background and objective Lactic acid bacteria (LAB) are generous producers of many industrially important products. Of these products, optically pure lactic acid is of great value as it is essential for production of highly crystalline poly-lactic acid, which is the most widely used biodegradable synthetic polymer. Hence, this study aimed to screen for thermotolerant LAB from a new source, which is fresh water samples collected from the coast of the Nile River, Egypt, and then evaluate their ability to produce optically pure L-lactic acid. Materials and methods LAB strains were isolated at 50°C and evaluated for producing optically pure L-lactic acid using high-performance liquid chromatography and BF-5. Effects of medium containing different sugar sources, incubation temperature, and initial pH of the medium on the purity and productivity of L-lactic acid were also studied. Results and discussion All obtained isolates were capable of producing optically pure L-lactic acid on different sugar sources. Changing the incubation temperature to 30°C positively affected both productivity and optical purity, which reached 5.0 g/l of 100% optically pure L-lactic acid. On the contrary, pH of the medium was confirmed to be also one of the major factors affecting productivity and optical purity of obtained L-lactic acid. For our isolates, pH 7.0 was the optimum one for the production process. The four promising producers of 100% optically pure L-lactic acid were molecularly identified as Lactiplantibacillus sp. Conclusion This is the first study describing the evaluation of the ability of fresh water LAB isolated from the Nile River to produce optically pure L-lactic acid.