Interaction of uranium (VI) with bacteria: potential applications in bioremediation of U contaminated oxic environments

Uranium and other metallic wastes released due to geochemical and several anthropogenic activities cause enormous damage to the environment. The fate and mobility of uranium (U) in the environment is affected by diverse microorganisms which interact through different mechanisms. Uranium at contaminated sites exists predominantly in two most common and stable valence states forms-the most oxidized valence state U(VI) exists as the highly soluble and toxic uranyl species (UO2 (2+)) while the reduced insoluble and less mobile, U(IV) is stable in the form of the mineral uraninite (UO2) under anoxic conditions. Reduced U(IV) species is less toxic and poorly soluble but it is liable to reoxidation and subsequent remobilization to soluble and more toxic U(VI) under oxic conditions. Fundamental understanding of nonreductive bacterial interaction mechanisms affecting the mobility and solubility of U(VI) in the environment is useful for developing suitable remediation and long-term management plan for U-contaminated sites. The present study gives an overview of various nonreductive bacterial interaction processes which affects the mobility and solubility of U(VI) in oxygenic environments.