The research goal of this proposal is to understand and evaluate the potential of using the aerobic bacterium Caulobacter crescentus for the application of uranium bioremediation. Previous work by our group and others has shown that C. crescentus has great potential to be used in uranium (U) bioremediation. Caulobacter is not only known for its ubiquitous presence in every type of aquatic community and many soils, but also its extremely high tolerance to U(VI). Despite the high solubility and cellular toxicity of U(VI), C. crescentus is able to mediate U biomineralization through its phosphate metabolism forming uranium phosphate minerals. The focus of the proposed work is to better characterize the biogenic U phosphate minerals formed by C. crescentus and help better understand the environmental factors affecting the biomineralization process and stability of these minerals. Specifically, we will focus on characterizing biogenic mineral phase and structure, and investigating the function of cells and cell surface structures and biomolecules that facilitate U precipitation at U concentrations relevant to the contaminated sites. Our long-range goal is to use the knowledge gained in this work to aid the development of a widely applicable conceptual model of the role of microbes in regulating contaminant U cycling in oxidizing environments across the DOE complex, and ultimately provide DOE with the scientific basis to support decisions for the remediation of legacy sites.