(436f) D-Lactic Acid Production By Indigenously Isolated Strains of Terrilactibacillus Laevilacticus from Soil Samples in Thailand

To date, the limitation of petroleum resources and the concerning consumption of oil-based plastics are being grown. Thus, the development of alternative bio-based raw materials is becoming interested. Lactic acid has long been recognized as a useful reagent that emerged in a wide range of industries. One of the most promising applications is a precursor for manufacturing polylactic acid (PLA) which can be biocompatible and biodegradable material. In order to synthesize PLA, the enantiomerically pure L- or D-lactic acid plays a crucial role to improve the stability, mechanical performance, and hydrolysis resistance of the polymer. Currently, lactic acid production is extensively commercialized via the biotechnological process to achieve high purity of lactic acid isomer. Industrially, L-lactic acid production is higher demand because of its applications in the food and pharmaceutical industries. In contrast, large scale production of D-lactic acid has not yet been commercialized; nevertheless, D-lactic acid production has been gained attention due to the demand for producing thermostable PLA. Therefore, it is interesting to develop a D-lactic acid production platform for economical and industrial aspects. Accordingly, a robust lactic acid-producing strain has been now considered as one of the most important criteria for large scale production of D-lactic acid. Wild-strain isolation strategy has long been employed to serve the industrial requirements, such as high yield, production rate, and optical purity. This study discovered two D-lactate producers from soil samples collected in Thailand by which they consequently identified as Terrilactibacillus laevilacticus SBK35-1 and T. laevilacticus SBK37-1, gram-staining positive, facultatively anaerobic, and endospore-forming rods with catalase-positive activity. In primary screening of lactic acid production, the results revealed that both strains were homofermentative D-lactic acid bacteria which produced lactic acid concentration of 86.90 g/L and 63.35 g/L, conversion yield of 75% and 60%, productivity of 1.81 g/L·h and 1.32 g/L·h for SBK35-1 and SBK37-1, respectively. Additionally, an optically pure D-isomer of lactic acid (100%) was obtained by these two strains when cultivated in glucose medium (120 g/L) under aerobic condition. Due to little information on this genus, the strain SBK35-1 could be considered as an alternative lactate producer for further study to achieve a suitable condition for effective D-lactic acid production by the genus Terrilactibacillus member.