Microbial metal-binding mechanisms and their relation to nuclear waste disposal

The cell surface polymers of microorganisms readily bind a variety of metal ions, which enables the organisms to immobilize potentially toxic metal ions before they encounter the plasma membrane. Under appropriate chemical conditions, bound metal ions can form a variety of minerals that may be of major geological importance. Many studies have shown the occurrence of metal binding and biomineralization in nature, but detailed knowledge of the underlying mechanisms is lacking. The microbial influence of this binding may be indirect, such as physicochemical influences on the solution chemistry, E(h), and pH; or direct, when it is determined by the type of organisms present, their energy metabolism, and the structural and chemical characteristics of the cell surface and extracellular polymers. Metal binding by bacterial cell surfaces has several implications in nuclear waste disposal including adsorption of soluble radionuclides. A detailed knowledge of the chemical mechanisms of metal interactions with the microbial cell surface will enhance our understanding of the geochemical environment within a nuclear waste disposal vault.