Biological properties and functions of five strains of lactic acid bacteria and three strains of Bacillus

Abstract:

[Background] Lactic acid bacteria (LAB) and Bacillus are commonly used probiotics in production, with different growth characteristics. It is essential to understand the biological characteristics of different strains. [Objective] To study the biological characteristics of the strains, develop and utilize the strains in a reasonable way, and ensure the safety of strain application in production. [Methods] After activation, five strains of LAB and three strains of Bacillus were identified. Their morphology was observed, and the growth curve, acid production, and optimal growth conditions of the strains were investigated. Furthermore, the antimicrobial activity, enzyme production, probiotic properties, and safety of the strains were measured. [Results] The strains R1-R5 of LAB were identified as Lactobacillus casei, L. paracasei, L. farcimini, L. futsaii, and L. salivarius, respectively. The strains Y1-Y3 of Bacillus were identified as B. velezensis, B. subtilis, and B. licheniformis, respectively. The eight strains presented different morphological structures but all were rod-shaped and entered the logarithmic growth stage and platform stage after being cultured for 2-10 h and 18-24 h, respectively. After incubation for 24 h, LAB and Bacillus maintained the viable counts at 10⁹ and 10⁸ CFU/mL, respectively, and the optimal growth at 37.0℃. LAB had strong acid-producing ability and antimicrobial activity, and Bacillus had strong enzyme production. All the strains demonstrated strong tolerance in artificial gastric juice, no hemolytic activity, no virulence gene, and moderate sensitivity to antibiotics. Among them, L. salivarius carried tetracycline resistance genes, while it was moderately sensitive to tetracycline. [Conclusion] The eight strains of bacteria have fast growth and reproduction. LAB have strong acid-producing ability and antimicrobial activity, and Bacillus has strong enzyme-producing performance. With good probiotic properties and safety in vitro, the 8 strains can be applied in production.

Key words:lactic acid bacteria;Bacillus;growth characteristics;biological function;probiotics