Radiometric determination of uranium accumulated in bacterial cells

A method for the radiometric determination of uranium accumulated in bacterial cells was investigated. Pseudomonas putida ATCC 33015 was grown in a medium containing uranium in the form of UO2(NO3)2. The cells were harvested by centrifugation, washed, resuspended in a buffer solution, ultrasonically disrupted and then suspended in Unisolve-1. The radiation emitted by natural uranium isotopes (mainly 238U and 234U) was measured by liquid scintillation counting with natural uranium as an internal standard. Mineralization of the samples was not required. Determination of the uranium content of bacterial cells was done either by comparing the radioactivity of the sample with that of standard samples or by using a calibration graph. The method was also used for determination of uranium in isolated subcellular fractions. Most of the uranium was associated with components of the cell membrane (lipids and polysaccharides), but part was bound to nucleic acids and microsomes. The relative standard deviation of the radiometric measurements did not exceed 5%. (author)