{'fraction_non_alphanumeric': 0.050102951269732326, 'fraction_numerical': 0.027453671928620454, 'mean_word_length': 4.902834008097166, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Characterization of Cadmium Uptake in Lactobacillus plantarum and Isolation of Cadmium and Manganese Uptake Mutants

ABSTRACT Two different Cd2+ uptake systems were identified inLactobacillus plantarum. One is a high-affinity, high-velocity Mn2+ uptake system which also takes up Cd2+ and is induced by Mn2+ starvation. The calculated Km and Vmaxare 0.26 μM and 3.6 μmol g of dry cell−1min−1, respectively. Unlike Mn2+ uptake, which is facilitated by citrate and related tricarboxylic acids, Cd2+ uptake is weakly inhibited by citrate. Cd2+ and Mn2+ are competitive inhibitors of each other, and the affinity of the system for Cd2+ is higher than that for Mn2+. The other Cd2+uptake system is expressed in Mn2+-sufficient cells, and noKm can be calculated for it because uptake is nonsaturable. Mn2+ does not compete for transport through this system, nor does any other tested cation, i.e., Zn2+, Cu2+, Co2+, Mg2+, Ca2+, Fe2+, or Ni2+. Both systems require energy, since uncouplers completely inhibit their activities. Two Mn2+-dependent L. plantarum mutants were isolated by chemical mutagenesis and ampicillin enrichment. They required more than 5,000 times as much Mn2+ for growth as the parental strain. Mn2+ starvation-induced Cd2+ uptake in both mutants was less than 5% the wild-type rate. The low level of long-term Mn2+ or Cd2+accumulation by the mutant strains also shows that the mutations eliminate the high-affinity Mn2+ and Cd2+uptake system.