Coprisin exerts antibacterial effects by inducing apoptosis-like death in Escherichia coli

Apoptosis commonly occurs in eukaryotes to eliminate unwanted cells. In this study, we demonstrated that coprisin-treated bacteria undergo cell death that is mechanistically and morphologically similar to apoptosis in eukaryotes. Time-kill kinetic assay against Escherichia coli indicated that coprisin exerted bactericidal activity. The bactericidal mechanism was studied by terminal deoxynucleotidyl transferase dUTP nick end labeling analysis, followed by Western blotting. We confirmed coprisin-induced DNA fragmentation and activation of the RecA protein as a SOS response. Furthermore, FITC-VAD-FMK, FITC-Annexin V, and bis-(1,3-dibutylbarbituric acid) trimethineoxonol [DiBAC₄(3)] staining showed that caspase-like protein(s), such as RecA, were activated, and membrane alterations such as phosphatidylserine externalization and cytoplasmic depolarization were induced. Finally, 3′-(p-hydroxyphenyl) fluorescein assay indicated that depolarization of membrane potential leads to hydroxyl radicals (^•OH) formation. Based on these results, we conclude that coprisin exerts bactericidal activity against E. coli by causing severe DNA damage, which induces apoptosis-like death.