FIGURE 1.

FetMP stimulates growth of an E. coli strain devoid of iron and manganese uptake systems. The fetMP operon or an antibiotic cassette control was inserted into the chromosome of strain ECA458 (ΔentC ΔfecABCDE ΔfeoABC ΔmntH ΔzupT), resulting in strains ECA612 (glmS-fetMP) (black bars) and ECA611 (glmS-Gm) (white bars). Iron-limited cultures of both strains were diluted 400-fold into Tris-buffered (A and C) or MES-buffered (B) mineral salts medium at pH 7 (A), pH 5 (B), or pH 9 (C) without added iron or containing the chelator CDTA without further additives or containing CDTA plus the indicated metal salts (FeCl₃, FeSO₄ with 1 mm ascorbate, MnCl₂, or ZnCl₂). The cultures were cultivated at 37 °C with shaking. Turbidity was determined at 600 nm after 16 h (A) or 20 h (B and C). Averages of three independent experiments with S.D. values (error bars) are shown.