Plasmid Mediated Tolerance and Removal of Heavy Metals by Enterobacter sp

Abstract

Problem statement: The role of plasmid in the heavy metal resistance and accumulation by endophytic bacteria was investigated. Approach: The experimental results showed that high level plasmid mediated Cd²⁺ and Zn²⁺ resistance in this strain is due to decreased Cd²⁺ and/or Zn²⁺ uptake/accumulation by resistance strain. Results: Based on the fact that subsequent plasmid curing experiments demonstrated that the ability to grow in presence of Cd²⁺and Zn²⁺ was encoded by the 98 kb plasmid, whereas the ability to grow in presence of Pb²⁺ appeared to be encoded by the chromosome. The Cd²⁺ and Zn²⁺ removal capacity of the respective metal resistant strain (pBN4) were about 36 and 45 µg g^-1 DW respectively, while the removal capacity of the both metal by sensitive variant showed a significant high Cd²⁺ and Zn²⁺ removal capacity of 153 and 228 µg g^-1 DW respectively. Conclusion: The isolated endophytic Enterobacter was not only tolerant to heavy metals, but also bound considerable amount of heavy metals from the growth medium. The biosorbed order of the metals by parental strain and its cured derivatives strain based on the cell dry weight was found to be in the order of Pb²⁺> Zn²⁺>Cd²⁺.