Heavy metal tolerance genes: prospective tools for bioremediation

Abstract

Unlike compounds that can be broken down, the remediation of most heavy metals and radionuclides requires removal from contaminated sources. Plants can extract inorganics, but effective phytoextraction requires plants that produce high biomass, grow rapidly and possess high capacity-uptake for the inorganic substrate. Either the existing hyperaccumulator plants must be bred for increased growth and biomass, or that hyperaccumulation traits must be engineered into fast growing, high biomass plants. The latter approach requires fundamental knowledge of the molecular mechanisms in the uptake and storage of inorganics. Much has been learned in recent years on how plants and certain fungi chelate and transport cadmium. This progress has been facilitated by the use of Schizosaccharomyces pombe as a model system. As target genes are identified in a model organism, their sequences can be modified for expression in a heterologous host or aid in the search of homologous genes in more complex organisms. Moreover, as plant nutrient uptake is intrinsically linked to the association with rhizospheric fungi, elucidating metal sequestration in this fungus permits additional opportunities for engineering rhizospheric microbes to assist in phytoextraction.