| The ways in which microorganisms impact the form, distribution and fate of uranium near the Earth's surface were investigated. Uranium contamination of water, soil, and sediments is a major problem, commonly associated with uranium mines and sites where uranium was processed for manufacture of weapons or for energy generation. Research presented here focused on uranium transformations that occur in anaerobic, microaerobic, and aerobic sediments and soils.; This research has demonstrated biological uranium reduction in the natural environment for the first time. Enzymatic uranium reduction by the Gram-positive Desulfosporisinus sp. was established, expanding the number of taxa known to carry out this important transformation. The size and size-dependent morphology, structure, and crystal growth pathways of biogenic uraninite were determined, yielding new understanding of the form and reactivity of this material in the environment. Our results clarify the importance of enzymatic rather than indirect uranium reduction and provide insights into the makeup of microbial communities in zones of active uranium cycling in shallow sediments. Uranium resistance of high G+C Gram-positive Arthrobacter ilicis was determined and the detoxification mechanism with poly phosphate granules was revealed. Deinococcus radiodurans, the most radiation-resistant organism known, was sensitive to chemical toxicity of uranium. These findings enhance our understanding of the geomicrobiology of uranium in the natural environment. The data have relevance to understanding of biogeochemical uranium cycles in the past, as well as the present, and provide important insights relevant to environmental cleanup of uranium-contaminated sites. |
