Abstract
Soils contaminated with heavy metals present a major threat to nodule-forming rhizobia, legumes, and symbiosis formed by the interacting symbionts. The symbiotic relation, as it occurs generally in economically important legumes, has deep impact on human interest. However, in legume–Rhizobium symbiosis, maximum yield is possible only when there is suitable condition for both symbiotic partners. Thus, understanding the effects of heavy metals on rhizobia–legume symbiosis will be useful. Although mechanical and chemical processes have been used to clean up metal-contaminated soils, most traditional remediation technologies do not provide acceptable solutions for the removal of metal from soils. The use of metal tolerant/detoxifying microbes offers a viable and inexpensive alternative technology to clean up polluted soils. Metal-tolerant microbes not only help to remediate the contaminated soils, but also provide elements essential to the growing legumes. Given the importance of legumes in animal and human consumption and their role in maintaining soil fertility, attention is paid to understand how rhizobia develops resistance to various heavy metals. Possible role of symbiotic nitrogen fixers in the metal-contaminated soils and how these microbes influence the productivity of various legumes in metal-contaminated soils across different geographical regions are discussed.