Characterization of lactic acid-producing bacillus coagulans strains with their antibacterial activity and l-lactic acid production

Abstract

Objectives: The objective is to study the screening of antibacterial activity, identification, and L-lactic acid production of spore-forming Bacillus isolates. Materials and Methods: Fourteen Bacillus isolates were characterized based on their phenotypic characteristics and 16S rRNA gene sequence analyses. The antibacterial activity was determined by agar diffusion method, and lactic acid production was analyzed using a high-performance liquid chromatography. Four isolates that produced above 85.0 g/L of lactic acid were selected for lactic acid fermentation using mid-log seed culture. Results: All isolates were identified as Bacillus coagulans based on the phenotypic characteristics and 16S rRNA gene sequence similarity (99.02–99.78 %). Strain JC-15 and JC-16 exhibited antibacterial activity against Kocuria rhizophila ATCC 9341. All isolates produced L-lactic acid ranged from 56.7 ± 0.54 to 92.05 ± 0.23 g/L at 37°C under microaerophilic conditions with 99.12 ± 0.10–100 ± 0.00% optical purity of lactic acid. B. coagulans PP-16 showed highest L-lactic acid concentration at 92.05 ± 0.23 g/L, yield of 0.77 ± 0.00 g/g, and productivity of 0.96 ± 0.00 g/L.h. After controlled seed preparation conditions, the four selected strains produced L-lactic acid in the range of 93.25 ± 0.07–103.25 ± 0.21 g/L and 102.85 ± 0.49–111.85 ± 0.21 g/L at 37°C with 98.75 ± 0.00–99.70 ± 0.01 and 88.66 ± 0.02–99.60 ± 0.01% optical purity of lactic acid under microaerophilic and anaerobic conditions, respectively. Yield and productivity were also increased. Fermentation under anaerobic conditions showed higher L-lactic acid titers and yield, whereas microaerophilic conditions gave higher productivity. Strain PP-16 gave the highest optical purity in both conditions.