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.

本研究的目的是分离和鉴定从红海黄貂鱼的内部微生物群中分离出来的芽孢杆菌属作为潜在的益生菌。对分离株控制弧菌属黄貂鱼病原体能力的初步分析导致选择了一种高度拮抗的分离株。基于全基因组系统发育鉴定出最有效的分离株为Bacillus velezensisAMB-y1。次生代谢物的基因组挖掘确定了五个抗菌生物合成簇，它们产生芽孢杆菌素、芽孢杆菌烯、艰难梭菌素、大环内酯素和美沙西丁。基因组挖掘还鉴定了两个抗真菌生物合成簇，它们编码产生杆菌霉素 D 和芬霉素的基因。基因组挖掘还确定了一个未知的 NRPS-transAT-PKS 簇，它可能产生另一种具有抗生素活性的化合物。该菌株的进一步特征是评估潜在益生菌剂所需的非生物胁迫耐受性。选定的分离株在非生物胁迫耐受性方面取得了可喜的成果；pH 耐受范围为 4.0 至 8.0，能够耐受高达 0.4% 的胆汁盐和 0 至 6.5% 的氯化钠浓度。此外，该菌株显示出疏水性值 (31%) 以及更高的自动聚集值 (49.9%)，这表明其根据细胞表面特征粘附在肠壁上的潜在能力。评估了该菌株对抗菌素的敏感性和新型B. velezensis AMB-y1 有可能用作水产养殖中的益生菌，以控制海洋鱼类和黄貂鱼病原体。