Probiotic properties and whole genome information of Bacillus velezensis from Taihang chicken

Abstract:

[Background] Bacillus spp. are important sources of probiotic preparations for poultry. Recently, Bacillus spp. have attracted much attention because of their inhibitory activities against pathogens and survivability under stress. [Objective] To screen Bacillus with probiotic properties from Taihang chicken, providing potential candidates for developing probiotic preparations in poultry. [Methods] Fresh feces samples were collected from healthy Taihang chickens. Bacillus strains were isolated with the selection medium and identified by 16S rRNA gene sequencing and core single nucleotide polymorphism (SNP) analysis of the whole genome. The inhibitory activities of the strains against indicator pathogens were tested by the double-layer agar plate method. The tolerance of the strains was evaluated based on the survival rates after incubation at different conditions. The broth dilution method was employed to examine the antimicrobial susceptibility of the strains. Furthermore, bioinformatics tools and databases were used for sequence alignment and annotation of the genomes, and the safety of the strain and the synthesis of secondary metabolites associated with probiotic profiles were analyzed. [Results] Five strains of Bacillus velezensis were identified, and they inhibited the growth of pathogens. Additionally, the isolates posed high survival rates after incubation at harsh conditions. They were sensitive to 12 tested antimicrobial agents and did not carry mobile resistance genes or virulence genes. Finally, 16–20 biosynthetic gene clusters related to secondary metabolite synthesis were identified in the five strains by antiSMASH, which showed high similarity to the biosynthetic gene clusters of fengycin and surfactin with broad-spectrum antimicrobial properties. [Conclusion] We obtained five B. velezensis strains with broad-spectrum antimicrobial properties and safety in vitro, which served as candidates for developing Bacillus-based probiotic preparations used for poultry.

Key words:Taihang chicken;Bacillus velezensis;antimicrobial activity;secondary metabolites