Characterization of pyrazinone
metabolites differentially regulated
by ribosomal inhibitory stress in E. coli. (A) Dose-dependent
production of 1–7 in E. coli Nissle 1917 by erythromycin, as established by LC-MS. Compounds 6 and 7 are indistinguishable by the standard
LC-MS method. ERM, erythromycin. (B) Half-maximal inhibitory concentration
(IC50) analysis of E. coli Nissle 1917
in response to erythromycin. Gray area represents sublethal antibiotic
range examined for metabolite production. (C) Key NMR correlations
for representative pyrazinone 1. NMR spectra and analysis
for all metabolites can be found in the Supporting Information. COSY, blue bold. HMBC, red arrows. (D) Keto-form
is favored versus enol-form. (E) Structures of characterized bacterial
metabolites (1–7) and human-derived
epinephrine and norepinephrine. Revised pyrazinone tautomeric structure
of DPO (7) is shown. n = 3 biological
replicates. Data are mean ± SD; *P < 0.05,
**P < 0.01, ***P < 0.001,
****P < 0.0001. Two-tailed t-test.
ns, not significant.