Fabrication of biobeads expressing heavy metal-binding protein for removal of heavy metal from wastewater.

Heavy metals, being toxic in nature, are one of the most persistent problems in wastewater. Unabated discharge of large amount of heavy metals into water bodies are known to cause several environmental and health impacts. Biological remediation processes like microbial remediation and phytoremediation are proved to be very effective in the reduction of heavy metal pollutants in wastewater. To circumvent the issues involved several peptides and proteins are being explored. Metal-binding capacity, accumulation, and tolerance of heavy metals in bacteria can be upsurge by overexpressing the genes which code for metal-binding proteins. In the present study, an attempt has been made to bioremediate heavy metal toxicity by overexpressing metal-binding proteins. Two expression cassettes harboring top4 metal-binding protein (T4MBP) and human metallothionein 3 (HMP3) were designed under the control of constitutive CaMV 35S promoter and transformed into E.coli TBI cells. E.coli over expressing HMP3 and T4MBP were immobilized in biobeads which were explored for the detoxification of water contaminated with copper and cadmium. Effects on the concentration of heavy metal before and after treatment with beads were estimated with the help of ICP-OES. Noteworthy results were obtained in the case of copper with 87.2% decrease in its concentration after treatment with biobeads. Significant decrement of 32.8% and 27.3% was found in case of zinc and cadmium, respectively. Mechanisms of binding of proteins with heavy metals were further validated by molecular modeling and metal-binding analysis. HMP3 protein was found to be more efficient in metal accumulation as compared with T4MBP. The fabricated biobeads in this study definitely offer an easy and user-handy approach towards the treatment of toxic wastewater.