Genome-wide screen of Escherichia coli Keio mutant line identifies genes related to propolis effect

Propolis, a natural bee product and functional food, exhibits potent antimicrobial properties. This study investigates the effect of propolis on Escherichia coli K-12 using the Keio genome-wide knockout mutant line, which contains single deletions of 3985 non-essential genes. 54 mutants showed sensitivity to propolis at sub-lethal concentrations for the wild type strain. The most sensitive mutants lacked the genes related to iron uptake by ferric enterobactin (FepD, FepA), glutamine transport (GlnP) and peptidoglycan recycling (LdcA). Complementation of these mutants with the corresponding genes restored resistance, suggesting that FepD, FepA, GlnP and LdcA play critical roles in providing intrinsic resistance to the antimicrobial effect of propolis. All 54 sensitive mutants were also classified into highly sensitive (HS, n = 4), moderately sensitive (MS, n = 14) and low sensitive (LS, n = 36) based on the level of growth inhibition. EcoCyc and Omics Dashboard analyses showed that the systems most affected by propolis were regulation, cell exterior, central dogma and other pathways. Enrichment of propolis sensitive gene hits using DAVID pathway analysis revealed the importance of ferric-enterobactin transport and metalloaminopeptidase activities. As a result of testing 3985 mutants, this study sheds light on the antimicrobial effect of propolis and the cellular adaptation of E. coli by providing molecular targets and pathways.