Microbial diversity in uranium contaminated soils

Contamination of soils with heavy metals and radionuclides is a severe environmental problem. Bacteria are involved in migration and detoxification of a large number of toxic metals due to their ability to interact with and to biotransform them. Total DNA was extracted from soils of one uranium mining waste pile near the town of Johanngeorgenstadt (Germany) and of one uranium mill tailings near Shiprock, NM in the USA. Universal bacterial, archael and also Geobacter-specific primers were used to construct 16S rDNA libraries. We found that natural microbial communities at the two uranium wastes differed significantly. Alpha-Proteobacteria and representatives of the Holophaga/Acidobacterium phylum were predominant in the U mining waste pile, whereas the Shiprock U mill tailings was occupied mainly by Bacillales, Gamma-Proteobacteria and Green non-sulfur bacteria. The most related sequences to ours in the GenBank were those of not yet cultured bacteria or archaea. Representatives of the genus Geobacter were identified in the U waste pile by using Geobacter-specific primers and in the U mill tailings by both Geobacter-specific and universal primers. Because these bacteria are able to reduce and immobilize a large number of heavy metals, we are performing a quantification of them via Real time PCR. Efforts to cultivate some bacterial isolates from the U wastes are in progress in our laboratory.

VAAM-2004 vom 28.03-31.03.04 in Braunschweig