Genome-based identification and purification of bacteriocin Q13 against methicillin-resistant Staphylococcus aureus from Lactococcus lactis Q13

Methicillin-resistant Staphylococcus aureus (MRSA) is widely acknowledged as a significant threat to food safety and human health. This research focused on the characteristics of bacteriocin Q13 produced by Lactococcus lactis Q13 isolated from the traditional Chinese fermented food hairy tofu. The gene clusters involved in the biosynthesis of bacteriocins were identified via whole genome sequencing of L. lactis Q13, indicating its ability to produce bacteriocins. The cell-free supernatant of L. lactis Q13 exhibited a significant bacteriostatic effect against MRSA, as well as the ability to combat a wide range of Gram-positive bacteria. Subsequently, bacteriocin Q13 was purified through ammonium sulfate precipitation, Sephadex G-50 gel filtration chromatography, and reversed-phase high-performance liquid chromatography (RP-HPLC). Its molecular weight was determined to be 19367.97 Da by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). Structural characterization using Fourier-transform infrared spectroscopy (FT-IR) indicated that the major secondary structures of bacteriocin Q13 were β-turn and β-sheet. Additionally, bacteriocin Q13 demonstrated remarkable stability under various environmental conditions, including enzymes, organic solvents, surfactants, metal ions, UV exposure, NaCl concentration, and storage time and temperature. Scanning electron microscopy (SEM) analysis showed that bacteriocin Q13 was able to induce significant morphological changes in MRSA, including disruption of cellular morphology, impairment of membrane integrity, and leakage of cytoplasmic contents, revealing the bacteriostatic mechanism of bacteriocin Q13 against MRSA. These results lay a scientific foundation for the application of L. lactis Q13 and its bacteriocin in the food industry as potential probiotics and preservatives.