Plasmid Mediated Tolerance and Removal of Heavy Metals by Enterobacter sp

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 Cd and Zn resistance in this strain is due to decreased Cd and/or Zn uptake/accumulation by resistance strain. Results: Based on the fact that subsequent plasmid curing experiments demonstrated that the ability to grow in presence of Cdand Zn was encoded by the 98 kb plasmid, whereas the ability to grow in presence of Pb appeared to be encoded by the chromosome. The Cd and Zn removal capacity of the respective metal resistant strain (pBN4) were about 36 and 45 μg g DW respectively, while the removal capacity of the both metal by sensitive variant showed a significant high Cd and Zn removal capacity of 153 and 228 μg g 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 Pb> Zn>Cd.