Genetic engineering in Bioremediation

4. Heavy metal detoxification

Heavy metals like mercury (Hg), lead (Pb), cadmium (Cd), arsenic (As), and chromium (Cr) are toxic, persistent in the environment, and bioaccumulative. They contaminate soil, groundwater, and ecosystems due to mining, industrial discharge, and improper waste disposal.

Unlike organic pollutants, heavy metals cannot be degraded — they must be immobilized, transformed into less toxic forms, or extracted. Genetic engineering enhances the efficiency of microbes and plants in achieving this.

Genetic Engineering Strategies

1.Metal Resistance Gene Transfer

Introducing genes that allow microbes to tolerate or transform metals. Example: merA and merB genes for mercury resistance and volatilization ;arsC gene for arsenate reduction.

2.Metal Transporter Engineering

Enhancing or introducing transporter proteins that pump metals into or out of cells. Example: Overexpression of ATP-binding cassette (ABC) transporters to sequester heavy metals in vacuoles or vesicles.

3. Phytoremediation Enhancement

Engineering plants to absorb and store heavy metals in tissues. Example: Transgenic Indian mustard with bacterial metal transporter genes (AtPCS1) for lead and cadmium uptake.

4.Metallothionein and Phytochelatin Gene Insertion

Metallothioneins (MTs) and phytochelatins (PCs) are metal-binding proteins/peptides. Example: Bacteria or plants modified to overproduce MTs and PCs show enhanced metal tolerance and accumulation.

5. Redox Transformation Genes

Engineering microbes to change the oxidation state of metals to less toxic or less mobile forms. Example: Reduction of Cr(VI) to Cr(III) by engineered Pseudomonas species. Arsenate (As⁵⁺) to arsenite (As³⁺) transformation by genetically modified E. coli.

 Engineered Microbial Examples