Isolation and characterization of Bacillus stratosphericus K as a sustainable probiotic for biocontrol of Edwardsiella ictaluri in Pelteobagrus fulvidraco aquaculture.

AIM: The yellow catfish, Pelteobagrus fulvidraco, is a major aquaculture species in China, but its intensive farming is threatened by bacterial diseases, particularly those caused by Edwardsiella ictaluri. The overuse of antibiotics to control these infections has led to concerns about resistance and environmental safety. This study aimed to isolate and characterize a novel antagonistic bacterial strain as a potential probiotic for sustainable disease management in P. fulvidraco aquaculture. METHODS AND RESULTS: In this study, a novel antagonistic bacterial strain, designated K, was isolated from soil samples collected on the East Lake Campus of Zhejiang A & F University. Through a polyphasic taxonomic approach, including morphological observation, physiological and biochemical assays, and 16S rDNA gene phylogenetic analysis, strain K was identified as Bacillus stratosphericus. The strain exhibited significant antagonistic activity against E. ictaluri, Citrobacter freundii, and Photobacterium damselae subsp. damselae. Optimal growth was observed at pH 6.4, 28°C, and 1.2% NaCl, indicating good adaptation to typical aquaculture conditions. Moreover, the strain showed broad susceptibility to commonly used antibiotics, supporting its potential safety as a probiotic candidate. Antagonistic substances extracted from the culture supernatant remained stable under various pH and temperature conditions, though their activity was affected by metal ions. In a challenge experiment, immersion in a suspension of B. stratosphericus K significantly enhanced the survival rate of P. fulvidraco following challenge with E. ictaluri. CONCLUSIONS: B. stratosphericus K was found to be a promising probiotic candidate with significant protective effects against E. ictaluri infection in P. fulvidraco aquaculture, highlighting its potential for sustainable disease management.