Genomic and phenotypic characterization of Bacillus velezensis AMB-y1; a potential probiotic to control pathogens in aquaculture

Authors: EMAM, ARAFAH - National Institute Of Oceanography And Fisheries; Dunlap, Christopher

Submitted to: Antonie Van Leeuwenhoek
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/1/2020
Publication Date: 10/23/2020
Citation: Emam, A.M., Dunlap, C.A. 2020. Genomic and phenotypic characterization of Bacillus velezensis AMB-y1; a potential probiotic to control pathogens in aquaculture. Antonie Van Leeuwenhoek. 113:2041–2052. https://doi.org/10.1007/s10482-020-01476-5.
DOI: https://doi.org/10.1007/s10482-020-01476-5

Interpretive Summary: An ARS researcher from Peoria, Illinois, collaborated with a scientist from Egypt to characterize a novel bacterial isolate of Bacillus from the intestine of a Tahitian stingray. Strains of Bacillus have been successfully commercialized as probiotics for use in poultry, livestock, and aquaculture feeds. The goal of this project was to isolate strains of Bacillus from the intestines of stingrays, which were antagonistic to a known fish pathogen (Vibrio sp.). One strain was identified and showed high activity to inhibit the pathogen while being able to tolerate the physiological stresses needed to be a probiotic. Future studies will explore the commercial potential of the strain as an aquaculture or poultry feed additive.

Technical Abstract: The aim of this investigation was to isolate and identify Bacillus species isolated from the internal microbiota of Red sea stingrays as potential probiotics. An initial assay on the ability of the isolates to control stingray pathogens of Vibrio species led to the selection of one highly antagonistic isolate. The most potent isolate was identified based on whole genome phylogeny as Bacillus velezensis AMB-y1. Genome mining for secondary metabolites identified five antibacterial biosynthetic clusters that produce, bacilysin, bacillaene, difficidin, macrolactin and mersacidin. Genome mining also identified two antifungal biosynthetic clusters which encode genes to produce bacillomycin D and fengycin. The genome mining also identified an unknown NRPS-transAT-PKS cluster that likely produced another compound with antibiotic activity. The strain was further characterized by the assessment of abiotic stress tolerances that are required in potential probiotic agents. The selected isolate had promising results in abiotic stress tolerance; pH tolerance within the range from 4.0 to 8.0, able to survive concentrations of bile salt up to 0.4% and sodium chloride from 0 to 6.5%. In addition, the strain showed a value of hydrophobicity (31%) along with a higher value of auto-aggregation (49.9%), which demonstrates its potential ability to adhere to the intestinal wall on the basis of its cell surface traits. The strain was evaluated for susceptibility to antimicrobials and the novel B. velezensis AMB-y1 has potential to be used as a probiotic in aquaculture to control marine fish and stingray pathogens.