Examination of cobalt uptake in the R. rhodochrous or E. coli transformants. (A) Cobalt uptake of the R. rhodochrous ATCC 12674 transformants. The reaction mixture consisted of 10 nM 57CoCl2, 10 mM MgCl2, and the cells in a 50 mM Tris·HCl buffer (pH 7.5). ○, R. rhodochrous ATCC 12674/pLJK50; ⋄, R. rhodochrous ATCC 12674/pLJK60; □, R. rhodochrous ATCC 12674/pK4. (B) Effect of other transient metals on the cobalt uptake of the R. rhodochrous ATCC 12674/pLJK50. Each metal was added at the final concentration of 5 μM, 10 min before the addition of 57CoCl2 into the cell suspension. □, MnCl2; ▵, FeSO4; ○, NiCl2; ⊞, CuSO4. (C) Cobalt uptake by the E. coli JM109 transformants. The reaction mixture consisted of 10 nM 57CoCl2, 10 mM MgCl2 and the cells in a 50 mM Tris-hydrochloride buffer (pH 7.5). □, E. coli JM109/pLCO10; ○, E. coli JM109/pLCO20; ◊, E. coli JM109/pUC19.