Resistance to, and accumulation of, uranium by bacteria from a uranium-contaminated site

Heterothrophic bacteria were isolated from an acidic uranium-contaminated site. Five isolates and one reference strain, Deinococcus radiodurans, were studied for uranium accumulation and resistance to uranium. Cells were incubated in a pH 4 solution containing 80 ppm of U(VI) in the form of (UO₂)²⁺ for 1 hr. Three isolates closely related to high G+C gram-positive bacteria were resistant to (UO₂)²⁺. One of the high G+C Gram-positive isolates, closely related to Arthrobacter ilicis, accumulated uranium intracellularly as precipitates closely associated with polyphosphate granules. It is interpreted that sequestration of uranium into polyphosphate is a detoxification mechanism. Deinococcus radiodurans, the most radiation resistant organism known, was vulnerable to chemical toxicity of (UO₂)²⁺. D. radiodurans precipitated nanocrystals of a uranyl phosphate mineral extracellularly, probably as the result of phosphate release during cell lysis. It is possible that Arthrobacter spp. play important roles in natural attennuation and stimulated bioremediation of sites contaminated with radionuclides and toxic organic compounds.