Fig. 2: EmrE can confer either resistance or susceptibility in vivo.

a Biolog phenotype microarray results were sorted by hit score for all 240 compounds in the screen (see Methods). Scores above +3 or below −3 are considered resistance or susceptibility hits, respectively, based on the differential between functional (WT) and nonfunctional (E14Q-EmrE). The strongest resistance hits (red) and susceptibility hits (cyan) were tested in growth assays (C-F). b IC₅₀ curves of WT- (black) and E14Q-EmrE (red) are shown for ethidium bromide (dashed lines, resistance) and harmane (solid lines, susceptibility). N = 3 biologically independent bacterial colonies were examined over three independent experiments. Data were presented as mean value ± SD. Note that cells expressing WT-EmrE have a 40% lower IC₅₀ value than cells expressing E14Q-EmrE in the presence of harmane. MG1655 ∆emrE E. coli expressing WT-EmrE (black) or E14Q-EmrE (red) were grown in the presence of c 0.5 mM methyl viologen (MV²⁺), d 0.05 mM chelerythrine chloride (CC), e 0.1 mM 18-crown-6-ether, or f 0.13 mM harmane. As expected, E. coli expressing WT-EmrE survived in the presence of MV²⁺ and CC (c, d), but E. coli expressing E14Q-EmrE did not, consistent with a resistance phenotype. In contrast, E. coli expressing nonfunctional, E14Q-EmrE had a higher OD₆₀₀ at the stationary phase than E. coli expressing WT-EmrE in the presence of 18-crown-6-ether and harmane, (e, f), consistent with a susceptibility phenotype.