FIG 1.

ECF transporter subunits and eetB are essential for provisioning flavins to the extracytosolic ApbE homolog FmnB in L. monocytogenes. (A) Reaction catalyzed by AbpE/FmnB flavin transferases. (B) Genomic organization of L. monocytogenes genes addressed in this study. (C) Ferric iron reductase activity of L. monocytogenes strains grown in chemically defined medium. The dotted lines separate flavin auxotroph (wild-type) strains (n = 4), flavin auxotroph strains supplemented with extracellular FAD (n = 2), and flavin prototroph (+ribDEAHT) strains (n = 3). For the noncomplemented strains, statistical significance was determined by one-way analysis of variance (ANOVA) and Dunnett’s posttest using the wild type as the control. For the FAD- and ribDEAHT-complemented conditions, statistical significance was determined by performing a t test compared to the parental noncomplemented condition. (D) Flavinylation levels (flavinylated peptide ion count/total peptide ion count) of the indicated PplA tryptic peptides in flavin prototroph (+ribDEAHT) L. monocytogenes strains as assessed by MS. The data are shown as the means and standard deviations (SDs) from three independent experiments. Statistical significance was determined by one-way ANOVA and Dunnett’s posttest using the wild type as the control. ****, P < 0.0001; ns, not significant (P > 0.05).