Assessing probiotic potential and safety of endophyte Paenibacillus polymyxa ZJNR2 isolated from Ardisia japonica
Probiotics represent a promising and environmentally sustainable alternative to antibiotic growth -promoters. The purpose of this study was to evaluate probiotic properties and safety of Paenibacillus polymyxa ZJNR2 (P. polymyxa ZJNR2), an endophytic bacterium isolated from Ardisia japonica (A. japonica). The results indicated that the isolate exhibited favorable tolerance to both simulated gastrointestinal fluid (SGF, pH 2.0, 3.0, and 6.8) and bile salts (0.10–0.40%). After 4 h of exposure, the survival rates remained above 85% in gastrointestinal fluids and >90% in bile salts. The strain also displayed considerable auto-aggregation capability and cell surface hydrophobicity. Furthermore, the strain showed good antioxidant activity, as both its suspension and cell-free fermentation supernatant (CFS) scavenged >65% of 2,2-diphenyl-1-picrylhydrazyl (DPPH) radicals. The antioxidant activity of CFS remained stable under varying pH values (6.0–8.0), temperatures (25–70°C), and exposure to ultraviolet light. The strain was susceptible to most tested antibiotics. Absence of virulent genes, such as nhe, cytK, ces, plc, and hbl, were observed in the strain. Acute toxicity assessment demonstrated no acute toxicity in mice. Summarily, P. polymyxa ZJNR2 emerges as a viable and promising probiotic candidate, meriting potential utilization within the aquaculture and feed sectors.