Figure 4.

⁵⁵Iron uptake rate of the Synechocystis 6803 exbBD double-mutant strains cultured in standard BG11 medium. (a, b) Cells were grown in BG11 medium to logarithmic phase, harvested, washed and re-suspended in iron-free BG11 medium lacking citric acid and ferric ammonium citrate. For free iron uptake rate measurement, ⁵⁵FeCl₃ was added to the cell solutions at 100 nM (3.7 kBq ml⁻¹) complexed with 2.6 μM EDTA (a). For measurement of iron-siderophores uptake rate, 100 nM ⁵⁵FeCl₃ and 133 nM DFB were added (b). (c, d) Cells were grown in BG11 medium to logarithmic phase, and iron uptake experiments were conducted using the trace metal clean technique. The ⁵⁵iron was precomplexed with EDTA over 24 h, as described in Kranzler et al. (2011). (c) Uptake rates of Synechocystis wild-type and Mut13 supplied with the same total iron concentration (0.993 μM) but varying free Fe′ concentrations. (d) Uptake rates of cells supplied with the same free Fe′ concentrations (0.13 nM) but different total iron concentration. (e) Uptake rates of Synechocystis wild-type and Mut13 supplied with different iron concentrations. Note the two additional measurements. The data marked with asterisk ‘*' were obtained using the same experimental procedure as the data of panels (c) and (d), but the medium lacked EDTA and all organic compounds.