Isolation and characterization of Bacillus altitudinis JSHY-074: A potential probiotic candidate with antagonistic activity against highly lethal Vibrio parahaemolyticus.

Abstract

Objective: The highly lethal Vibrio disease (HLVD) caused by highly lethal Vibrio parahaemolyticus (VpHLVD) represents a significant threat to Pacific white shrimp Litopenaeus vannamei aquaculture. The existing disease control approaches often rely on antibiotics, leading to drug resistance and environmental pollution, thereby limiting the sustainable development of shrimp farming. Probiotics are recognized for their ability to enhance host disease resistance and to inhibit pathogenic bacteria with high safety and environmental friendliness.

Methods: We evaluated the potential of a probiotic bacterial dietary supplement for HLVD prevention. Bacillus altitudinis strain JSHY-074, isolated from coastal aquaculture environments in Jiangsu, China, was identified based on morphological characterization, 16S ribosomal DNA sequencing, and whole-genome analysis. Its antagonistic activity against V. parahaemolyticus strain SHY1669 was determined by co-culture inhibition tests, and the probiotic effect was verified through a VpHLVD challenge experiment on Pacific white shrimp fed with JSHY-074.

Results: The strain JSHY-074 exhibited potent antagonistic activity against V. parahaemolyticus strain SHY1669, with inhibition zones expanding from 12 ± 0.31 mm (mean ± SD) at 6 h of co-culture to 30 ± 0.84 mm at 96 h of co-culture. At an inoculum density of 1.0 × 108 CFU/mL, the inhibition rate reached 88.58% at 72 h. Whole--genome analysis revealed nine gene clusters associated with secondary metabolite production, with lichenysin preliminarily identified as the primary active compound. The VpHLVD challenge experiment demonstrated that feeding Pacific white shrimp with strain JSHY-074 achieved a 70% survival rate within 5 d and a 5,942-fold reduction in hepatopancreas pathogen load (from 6.12 × 107 to 1.03 × 104 copies/ng).

Conclusions: This is the first report of B. altitudinis exhibiting antagonistic activity against VpHLVD. The high technological readiness level of B. altitudinis JSHY-074 makes it a versatile probiotic feed additive, and its safety and effectiveness make it well suited for fast deployment and use in shrimp farming, offering a nutritional approach to reducing antibiotic dependency and promoting sustainable aquaculture practices.