Honglian Tan

Pathogenic Vibrio species are a major cause of disease outbreaks in aquaculture, leading to substantial economic losses and posing risks to food safety. The increasing prevalence of antibiotic resistance among these pathogens has created an urgent need for alternative antimicrobial strategies. Phage-derived endolysins, which specifically degrade bacterial peptidoglycan, have emerged as promising candidates to replace or supplement conventional antibiotics. In this study, we systematically characterized the endolysin LysV039C from the Vibrio alginolyticus phage phiV039C. Whole-genome analysis identified a 462 bp endolysin gene, which was cloned into the pET-28a vector, expressed in E. coli BL21, and purified. The lytic activity of the recombinant enzyme was evaluated using a turbidity reduction assay. LysV039C showed the strongest activity (58.9%) against host bacteria in the logarithmic phase, with peak activity (60.7–64.1%) achieved at 53 μg/mL, 35 °C, and neutral pH. The addition of 2.5 mM EDTA enhanced activity to 63.8%, whereas 10 mM divalent metal ions strongly inhibited the enzyme (Vibrio species than its parent phage phiV039C. Overall, LysV039C combines high environmental adaptability (alkaline tolerance, suitability for aquaculture temperature ranges) with efficient and broadened lytic activity against multiple Vibrio species. These findings provide a foundation for developing eco-friendly agents for the prevention and control of pathogenic Vibrio and offer a valuable reference for the mining of other phage-derived antibacterials against aquatic pathogens.

The escalating problem of copper (Cu) and cadmium (Cd) pollution in aquatic environments poses a significant threat to the ovarian tissue and reproductive capacity of fish, hindering the development of the aquaculture industry. However, the combined effects of Cu and Cd on fish gonadal development remain unclear. In this study, the fish species Nile tilapia was stressed with rearing water containing 300 μg/L Cu²⁺ and 100 μg/L Cd²⁺ for 30 days, followed by an intraperitoneal injection of luteinizing hormone-releasing hormone (LHRH-α) and human chorionic gonadotropin (HCG) at various concentrations. We investigated the ovarian transcriptome profiles before and after injection. Prior to injection, combined treatment with Cu and Cd resulted in reproductive dysfunction and metal ion imbalance in tilapia. Transcriptomic profiling revealed differential gene annotation concentrated in the MAPK signaling pathway and regulation of GTPase activity. Post-injection, all concentrations of LHRH-α and HCG groups showed an upregulated gonadosomatic index (G.S.I) and higher levels of vitellogenin (VTG), gonadotropin-releasing hormone (GnRH), gonadotropin (GTH), and estrogen (E2) in serum compared to the negative control group. Transcriptomic analysis revealed alterations in various ovarian signaling pathways, preliminarily revealing the in vivo molecular mechanisms and differences in LHRH-α and HCG. The findings from this study could help us better understand how to counteract the effects of combined Cu and Cd exposure on tilapia ovarian development, which has significant implications for the Nile tilapia aquaculture industry.