Characterization of cadmium uptake in Lactobacillus plantarum and isolation of cadmium and manganese uptake mutants.
Two different Cd(2+) uptake systems were identified in Lactobacillus plantarum. One is a high-affinity, high-velocity Mn(2+) uptake system which also takes up Cd(2+) and is induced by Mn(2+) starvation. The calculated K(m) and V(max) are 0.26 microM and 3.6 micromol g of dry cell(-1) min(-1), respectively. Unlike Mn(2+) uptake, which is facilitated by citrate and related tricarboxylic acids, Cd(2+) uptake is weakly inhibited by citrate. Cd(2+) and Mn(2+) are competitive inhibitors of each other, and the affinity of the system for Cd(2+) is higher than that for Mn(2+). The other Cd(2+) uptake system is expressed in Mn(2+)-sufficient cells, and no K(m) can be calculated for it because uptake is nonsaturable. Mn(2+) does not compete for transport through this system, nor does any other tested cation, i.e., Zn(2+), Cu(2+), Co(2+), Mg(2+), Ca(2+), Fe(2+), or Ni(2+). Both systems require energy, since uncouplers completely inhibit their activities. Two Mn(2+)-dependent L. plantarum mutants were isolated by chemical mutagenesis and ampicillin enrichment. They required more than 5,000 times as much Mn(2+) for growth as the parental strain. Mn(2+) starvation-induced Cd(2+) uptake in both mutants was less than 5% the wild-type rate. The low level of long-term Mn(2+) or Cd(2+) accumulation by the mutant strains also shows that the mutations eliminate the high-affinity Mn(2+) and Cd(2+) uptake system.
Hao
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Institute for Comparative and Environmental Toxicology, Cornell University, Ithaca, New York 14853, USA.
Reiske
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Wilson
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D001692:Biological Transport / Q000187:drug effects; D002104:Cadmium / Q000378:metabolism* / Q000494:pharmacology; D002413:Cations, Divalent / Q000378:metabolism / Q000494:pharmacology; D007700:Kinetics; D007778:Lactobacillus / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism*; D008345:Manganese / Q000378:metabolism* / Q000494:pharmacology; D009154:Mutation
D002413:Cations, Divalent; D002104:Cadmium; D008345:Manganese