Biotechnological Approaches for Enhancing Phytoremediation of Heavy Metals and Metalloids

Phytoremediation, the use of plants and their associated microbes to accumulate, detoxify and/or stabilise contaminants, is an environment‐friendly and sustainable means of remediating contaminated soil and water. Phytoremediation has been an important aspect of constructed wetlands, which have been used successfully to detoxify large volumes of wastewater with dilute concentrations of contaminants. The usefulness of phytoremediation appears to extend to a wide variety of contaminants, and a recent study demonstrated its possible application for selenocyanate. Genetic engineering approaches are currently being used to optimise the metabolic and physiological processes that enable plants to phytoremediate sites contaminated with heavy metals and metalloids. Over‐expressing enzymes catalysing rate‐limiting steps in the sulphate assimilation and phytochelatin synthesis pathways has been shown to confer increased tolerance to and the ability to accumulate higher concentrations of selenium and cadmium, respectively. Recent research in our laboratory is aimed at determining the regulatory genes involved in heavy metal accumulation and detoxification in hyperaccumulating plants that could then be transferred to fast‐growing, high biomass plant species for phytoremediation. Microbes isolated from highly contaminated environments represent another potentially huge reservoir of new genes and unique metabolic capabilities that could be transferred to plants to enhance their phytoremediation potential.