Cadmium-resistant mutant of Bacillus subtilis 168 with reduced cadmium transport

Cd2+ and Mn2+ accumulation was studied with wild-type Bacillus subtilis 168 and a Cd2+-resistant mutant. After 5 min of incubation in the presence of 0.1 μM 109Cd2+ or 54Mn2+, both strains accumulated comparable amounts of 54Mn2+, while the sensitive cells accumulated three times more 109Cd2+ than the Cd2+ -resistant cells did. Both 54Mn2+ and 109Cd2+ uptake, which apparently occur by the same transport system, demonstrated cation specificity; 20 μM Mn2+ or Cd2+ (but not Zn2+) inhibited the uptake of 0.1 μM 109Cd2+ or 54Mn2+. 54Mn2+ and 109Cd2+ uptake was energy dependent and temperature sensitive, but 109Cd2+ uptake in the Cd2+-resistant strain was only partially inhibited by an uncoupler or by a decrease in temperature. 109Cd2+ uptake in the sensitive strain followed Michaelis-Menten kinetics. 109Cd2+ uptake in the Cd2+ -resistant strain was not saturable. The K/sub m/ and V/sub max/s for 54Mn2+ uptake by both strains were very similar. Cd2+ inhibition of 54Mn2+ uptake had an apparent K/sub i/ of 3.4 and 21.5 μM Cd2+ for the sensitive and Cd2+ -resistant strains, respectively. Mn2+ had an apparent K/sub i/ of 1.2 μM Mn2+ for inhibition of 109Cd2+ uptake by the sensitive strain, but the Cd2+ -resistant straian had no defined K/sub i/ value for inhibition of Cd2+ uptake by Mn2+