Figure 7. Effects of Ni²⁺ on growth of E. coli and Ni²⁺ accumulation in E. coli and in H. pylori.

(A) Growth curves of freshly inoculated cultures of E. coli BL21(DE3) both with and without the hpn gene (pET-hpn) in LB medium containing Ni²⁺ (as NiSO₄, 500 μM). (B) The influence of Hpn expression on the growth of E. coli BL21(DE3) cells cultured in LB medium supplemented with NiSO₄ at 0, 50, 100, 200, 500 or 800 μM. ▼, +pET-hpn, with IPTG induction (0.5 mM); ▲, +pET-hpn, no IPTG induction; ●, −pET-hpn, with IPTG induction (0.5 mM); ■, −pET-hpn, no IPTG induction. (C) E. coli BL21(DE3) cells were cultured in LB medium supplemented with 500 μM NiSO₄, with or without the plasmid pET-Hpn, and with or without IPTG induction of Hpn expression. (D) The wild-type and Hpn-deleted H. pylori 26695 cells were cultured in fresh Brucella broth supplemented with 5% foetal bovine serum and 200 μM NiSO₄. The Ni²⁺ content associated with the cell pellet was determined using ICP-MS.