ABSTRACT
Heavy metals (HMs) are significant environmental pollutants, and their toxicity is a problem of increasing significance for ecological, evolutionary, nutritional, and environmental reasons. Phytoremediation is an emerging cleanup technology for contaminated soils, groundwater, and wastewater that requires minimal site disturbance and maintenance. Restoration of habitats and in situ cleanup of HM contaminants from a waste-polluted site can be achieved with this technology. Research is in progress to enhance the efficacy of this plant-based technology. In this context, rhizobacteria and endophytes seem promising to increase plant growth and biomass and assist phytoremediation of HMs in contaminated soil. Diazotrophs have the ability to affect HM mobility and availability to the plant through the release of chelating agents, acidification, phosphate solubilization, and redox changes. In addition, diazotrophs improve plant growth by atmospheric nitrogen fixation, phytohormone production, and plant protection from phytopathogens by the production of antibiotics or other pathogen-suppressing substances such as siderophores and chelating agents. In addition, some diazotrophs have the ability to decrease the level of ethylene in plants through the production of 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase, consequently increasing plant growth and biomass. The aim of the present chapter is to highlight the recent developments in phytoremediation of HM-contaminated soils, with particular reference to diazotrophs in the rhizosphere and endosphere of plants growing on such soils and their significance in phytoremediation.
