Isolation and functional characterization of a bacteriophage targeting pathogenic Bacillus cereus in Trionyx sinensis

Trionyx sinensis suffers from severe disease caused by pathogenic Bacillus cereus, necessitating the exploration of novel biocontrol technology. In this study, a new phage targeting B. cereus from T. sinensis, designated PSYJ-YH, was isolated and characterized. The phage particles feature an oval, polyhedral head and flexible tail fibers, classifying them as siphoviruses. At the multiplicity of infection (MOI) of 0.001, the phage titer reached the highest value of 1.39 × 10⁹ PFU/mL. PSYJ-YH exhibited moderate adsorption rate, with 86.3% of particles adsorbing within 21 min. The one-step growth curve revealed a latent period of 20 min and a burst size of 256.6 PFU/cell. The phage demonstrated stability across temperatures of 30-60 °C and pH values of 4-11. Its complete genome comprises a circular double-stranded DNA molecule of 46,577 bp, with a G + C content of 38.11%, encoding 79 putative open reading frames (ORFs). Genome analysis revealed low similarity to known phages, indicating that PSYJ-YH represents a novel species within an unclassified genus of the class Caudoviricetes. Phage administration reduced mortality, tissue and organ lesions, bacterial loads in organs, and inflammatory responses in B. cereus-infected T. sinensis. This study enhances our understanding of virulent phages for controlling bacterial infection in T. sinensis.