Genetically Modified Microbe Mediated Metal Bioaccumulation: A Sustainable Effluent Treatment Strategy

Abstract

Consistent increase in living standards of humans has resulted in a concomitant rise in demand for heavy metals that have become an indispensable component of electronics and are also extensively used as raw materials for infrastructure as well as advance material formulations. In order to supply such enormous demands, mining and metal-refinery industries often disregard environmental safety and carry out economically feasible but hazardous mining operations which include improper treatment of effluents. Hence, eco-friendly and sustainable mining practices are primarily essential with regards to wastewater effluents containing hazardous heavy metals that may pollute water bodies if discharged without any treatment. Conventional methods of heavy metal removal include chemical precipitation, coagulation/ flocculation, membrane filtration, photocatalysis and adsorption. However, these techniques often produce harmful by-products that require tedious disposal processes that in turn, increase energy requirements. Thus, genetically modified microbe mediated bioaccumulation is one of the alternative approaches for removal of heavy metals from industrial effluents that is cost-effective, eco-friendly and easy to operate. This chapter elaborates in detail application of such genetically modified bacteria for carrying out sustainable removal of heavy metals from effluents. Microbial bioaccumulation is a metabolically active process wherein several bacteria assimilate toxic elements such as arsenic, cadmium, mercury, copper, cobalt and zinc. Several studies have reported improvement of such uptake of heavy metals using genetic recombination and expression of channel proteins, secondary carriers and primary active membrane transporters in bacteria such as Escherichia coli, Corynebacterium glutamicum and Mesorhizobium huakuii. Additionally, some metal-binding proteins and polymers were also genetically encoded for facilitating improved bioaccumulation. Hence, development of bioaccumulation carried out by genetically engineered microorganisms (GEMs) for removal of heavy metals from industrial effluents could be a useful technology in order to alleviate environmental pollution.