An Oxygen-Responsive Metabolic Shift in Gut Bacterium Enterococcus faecalis Leads to Production of Imidazolium Antibiotics That Disrupt the Proton Motive Force

High Resolution Image Download MS PowerPoint Slide Elevated oxygen levels in the intestine during antibiotic exposure and disease perturb gut communities, yet the metabolites underlying bacterial adaptation remain unclear. Here, we show that oxygen stress is associated with increased production of a family of antibacterial imidazolium metabolites in the facultative anaerobe Enterococcus faecalis KCTC 5191 T . Comparative LC-MS profiling under aerobic versus anaerobic culture revealed increased accumulation of metabolites, including nine previously undescribed imidazoliums, enterozolium A–I. Uniform 13 C/ 15 N tracer feeding ( l -phenylalanine and l -tyrosine) established their origins as biogenic amines, and biomimetic syntheses corroborated the proposed structures and nonenzymatic steps. A tdc locus encoding tyrosine decarboxylase ( tyrDC ) was required for production of the amine precursors: a Δ tdc mutant of E. faecalis v583 showed markedly reduced metabolite levels and tyrDC transcripts increased ∼4-fold under aerobic conditions. Several metabolites were active against methicillin-resistant Staphylococcus aureus (MRSA); 10 and 17 displayed minimum inhibitory concentrations (MICs) of 5.2 and 3.1 μg/mL, respectively, and 17 showed efficacy in a Caenorhabditis elegans model of MRSA infection. Mechanistic assays indicate dissipation of the membrane proton motive force (PMF) as the antibacterial mode of action. These findings uncover an oxygen-responsive metabolic shift that yields PMF-targeting imidazolium antibiotics and highlight the imidazolium scaffold as a promising lead for antibacterial discovery.