Effect of Metal-Binding Antimicrobial Peptide SIF₄ on Topoisomerases Activity and Intracellular Nucleic Acid Biosynthesis in Escherichia coli

To systematically elucidate how metal-binding antimicrobial peptide SIF₄ exerts its antimicrobial activity by targeting DNA topoisomerase without destroying the cytoplasmic membrane, Escherichia coli was used as a model strain to investigate the binding mode of SIF₄ with its genomic DNA and the impact of SIF₄ on DNA topoisomerase Ⅰ and Ⅱ activities and intracellular nucleic acid biosynthesis. Results showed that SIF₄ could bind to genomic DNA in a manner similar to ethidium bromide (EB) intercalation with strong inhibitory effect on topoisomerase Ⅰ but weak effect on topoisomerase Ⅱ, and catalyzed RNA transcription to exert antimicrobial activity by interfering with the unwinding of negative DNA supercoils and RNA polymerase binding. It was also found that the biosynthesis of intracellular DNA and RNA was inhibited to different degrees after 12 h treatment with SIF₄, which exhibited a good dose-effect relationship. There was no significant difference in the amounts of intracellular DNA and RNA between the 1/2 minimum inhibitory concentration (MIC) group and the control group (P > 0.05), but there was a significant difference between the MIC and 2 MIC groups and the control group (P < 0.05). Our results may provide theoretical support for the application of SIF₄ in the biocontrol of foodborne E. coli.