FIG. 4.

Nickel transport of the E. coli HYD723 nik mutant as a function of HupE and HupE2 expression. Strain HYD723 derivatives harboring plasmid pBADE1 (hupE; ▴ in panel A) or pBADE2 (hupE2; ▪ in panel B) or control plasmid pBAD18-Kan (⧫ in both panels) were grown in Luria-Bertani medium under aerobic conditions at mid-log phase (OD₆₀₀, ≈0.5). Then, arabinose (final concentration, 200 μM) was added to induce PBAD expression. The uptake assay was performed in the presence of 150 nM ⁶³Ni²⁺ by using a cell density equal to that in the original culture for pBADE1 (A) or 10-fold higher for pBADE2 (B). Aliquots (100 μl) were filtered at the indicated times. The intracellular concentration of ⁶³Ni per milligram of bacteria (dry weight) (BDW) was determined. The values shown represent a typical experiment and are averages of results from two replicates, with error bars indicating standard deviations. Error bars smaller than the symbols are not shown.