水产源枯草芽孢杆菌的分离鉴定及其潜在益生特性分析OA

To screen for bacteria with potential probiotic effects on fish,this study performed isolation and identification of Bacillus strains from the intestinal contents of healthy fish and from aquaculture water samples.The obtained Bacillus isolates were subjected to in vitro probiotic characterization,including assessments of antibacterial activity,enzyme-producing potential,hemolytic activity,antibiotic susceptibility,growth curve,tolerance to simulated gastrointestinal fluids,adhesion capacity,and whole-genome sequencing analysis.The results showed that a total of 16 Bacillus strains were isolated,among which one strain,Bacillus subtilis GDGF26 3-1-1,was successfully selected.This strain exhibited strong antibacterial potential against two aquatic pathogens,Aeromonas hydrophila and Vibrio parahaemolyticus,with inhibition zone diameters≥15 mm.The strain also demonstrated strong enzyme-producing potential(hydrolysis zone diameters≥16 mm),displayed α-hemolytic activity,was susceptible to all eight tested antibiotics,grew well,and achieved a survival rate of 140.34%in simulated small intestinal fluid,along with notable auto-aggregation capacity and cell-surface hydrophobicity in vitro.Whole-genome sequencing revealed that the strain harbored genes associated with broad-spectrum antibacterial activity,antifungal activity,anti-biofilm formation,and environmental tolerance.It did not contain the unequivocally pathogenic core virulence genes,including those encoding cereulide,the hemolytic enterotoxin nhe gene complex(nheA,nheB,and nheC),and the enterotoxin FM gene(entFM).Moreover,the strain lacked acquired antimicrobial resistance genes with potential for horizontal transfer,while possessing the genetic basis for synthesizing multiple lipopeptide and polyketide antimicrobial compounds.Collectively,these findings indicate that B.subtilis GDGF26 3-1-1 exhibits considerable in vitro probiotic potential in terms of antibacterial activity,enzyme production,simulated intestinal fluid adaptability,and genetic safety,thereby representing a candidate strain for aquatic probiotics and providing a strain reference for subsequent evaluations of sporulation characteristics,formulation stability,and in vivo efficacy in aquatic animals.