ABSTRACT
This chapter discusses the potential impact of soil bacteria on heavy metal extraction by plants. Rhizosphere bacteria, including those which carry plasmid-borne resistances to heavy metals, may be expected to play an important role in the bioavailability of metals to the plant. Siderophores produced by plant growth-promoting rhizobacteria and bacterial biological control agents are associated with improved plant growth, either through a direct effect on the plant, through control of noxious organisms in the soil, or via some other route. Some plants utilize microbial ferric iron-siderophore complexes. Microbial hydroxamate type siderophores were used by plants, such as sunflower and sorghum, for the uptake of iron. Siderophore production can be stimulated by the presence of heavy metals. Metal-tolerant bacteria are isolated from many metal-rich biotopes, of either manmade or natural origins. The bacteria isolated from natural metal-rich biotopes belonged to various genera.
