Affiliation:
1. Institute for Comparative and Environmental Toxicology1 and
2. Department of Molecular Biology and Genetics,2 Cornell University, Ithaca, New York 14853
Abstract
ABSTRACT
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 μM and 3.6 μmol 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.
Publisher
American Society for Microbiology
Subject
Ecology,Applied Microbiology and Biotechnology,Food Science,Biotechnology
Cited by
36 articles.
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