The antibacterial activity and metabolomic analysis of the recombinant lectin protein PFL-96 derived from Pinctada fucata against Streptococcus agalactiae isolated from tilapia (Oreochromis niloticus).

Tilapia, a nutritious fish that is rich in protein and low in fat, is vulnerable to bacterial infections caused by Streptococcus agalactiae. This study represents the first investigation into the antibacterial efficacy and underlying mechanisms of the recombinant lectin protein PFL-96, derived from Pinctada fucata, against S. agalactiae isolated from tilapia. PFL-96 demonstrated significant antibacterial activity, with an inhibition zone measuring 21.11 ± 0.41 mm, and minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values of 8 μg/mL and 16 μg/mL, respectively. PFL-96 significantly inhibited bacterial growth and eliminated most bacteria within 12 h at MBC. Furthermore, PFL-96 disrupted the cell structure of S. agalactiae, leading to the leakage of nucleic acids, proteins, and potassium ions, while also increasing the production of reactive oxygen species (ROS), which ultimately induces bacterial death. Additionally, PFL-96 proved effective in inhibiting early biofilm formation and in eliminating established biofilms. Metabolomics analysis revealed that PFL-96 significantly altered intracellular metabolic processes, affecting 258 metabolites, with 204 being significantly down-regulated and 54 significantly up-regulated. These alterations primarily impacted cell wall structure, membrane stability, energy metabolism, and the expression of genetic material. In conclusion, PFL-96 exhibits potent antibacterial activity against S. agalactiae, with a complex mechanism of action. This study provides valuable insights and a theoretical foundation for the application of PFL-96 in the prevention and treatment of S. agalactiae infections in tilapia.