Bacterial responses to uranyl and sodium nitrate treatments and fate of the added U(VI) in uranium mining waste piles


Bacterial responses to uranyl and sodium nitrate treatments and fate of the added U(VI) in uranium mining waste piles

Geissler, A.; Merroun, M.; Geipel, G.; Reuther, H.; Selenska-Pobell, S.

The responses of the bacterial community of a uranium mining waste pile to increased concentrations of uranyl or sodium nitrate were studied in microcosm experiments under conditions corresponding to the natural. For this study, the 16S rRNA (Fig. 1) and the narG-gene retrievals were applied. Both retrievals demonstrated that at the early stages of the treatments with sodium nitrate a strong activation of nitrate reducing and denitrifying populations, mainly of Firmicutes and Betaproteobacteria, occurred; they had overgrown the Acidobacteria, Alpha-, and Deltaproteobacteria which originally predominated in the untreated samples. Due to the U(VI) toxicity only a few populations of the mentioned Firmicutes and betaproteobacterial nitrate reducers proliferated in the samples treated with uranyl nitrate. More significant for these samples was the stimulation of the gammaproteobacterial denitrifyers, able to effectively interact with the added uranium. After longer incubations both treatments resulted in an establishment of betaproteobacterial populations and also of populations characteristic for the original, non-treated sample. As measured by using Mössbauer spectroscopy, at these stages a strong reduction of Fe(III) to Fe(II) occurred in the samples. Time-resolved laser fluorescence spectroscopic analyses demonstrated that most of the added U(VI) was bound in uranyl-hydro-phosphate phases or was complexed by organic phosphate groups (Fig. 2). The phosphate groups were liberated by different kinds of bacteria due to the activity of their intrinsic acidic phosphatases or were supplied by the lysed cells of the dead parts of the numerically reduced populations. The latter was confirmed by X-ray structural analyses of the formed bacteria - uranium complexes in the studied samples. Our results demonstrate that bacteria in uranium mining waste piles possess a high potential to deal with increased, toxic concentrations of U(VI) and nitrate, which usually co-contaminate these environments.

  • Lecture (Conference)
    9th Symposium on Bacterial Genetics and Ecology (BAGECO 9), 23.-27.06.2007, Wernigerode, Germany

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Publ.-Id: 9632