Microbial communities in flooded underground uranium mines of East Germany

After the German reunification the Wismut GmbH, formerly the 3rd largest U producer of the world, started to remediate the legacies of their U mining activities. As a part of the remediation strategy, the pit body was flooded to induce reductive processes. Although flooding of the mines Pöhla and Schlema-Alberoda was already finished about ten years ago, the mine water still contains elevated concentrations of toxic metals such as U, As and Ra. Thus, expensive and long-lasting monitoring and waste water treatment is required. Since microorganisms can influence the toxicity of metals directly or indirectly, one alternative approach is to use them for bioremediation (Anderson and Lovley, 1997). To remediate U contaminated sites recent studies mainly focused on the applicaton of dissimilatory Fe(III) and sulfate-reducing microorganisms, which are capable to reduce U(VI) to U(IV) thus resulting in a decreased U mobility (Lovley and Philips, 1992; Lovley et al., 1993). Here, the diversity of the indigenous microbial community of the mine water from Pöhla, Schlema-Alberoda and an older uranium mine site, Zobes, is reported. Bacteria as well as Archaea were analyzed by state-of-the-art pyrosequencing of the 16S rRNA gene. Mine water samples were either filtrated (10 l) or harvested from an in situ flow cell. For the Zobes site natural biofilms grown on activated carbon were also collected. The analysis of the bacterial diversity of the Pöhla mine water resulted in 1196 sequences which represent members of the Proteobacteria, Verrumicrobia, Bacteriodetes, WS3, Chloroflexi, Firmicutes, Acidobacteria, SR1, Actinobacteria, Spirochaetes and OD1. For the Schlema-Alberoda mine water 1915 sequences were analysed which were divided into the nine following phyla Proteobacteria, Acidobacteria, WS3, Bacteriodetes, Chloroflexi, SR1, Chlorobi, TM7 and Actinobacteria. In comparison to the mine water of Pöhla and Schlema-Alberoda the bacterial composition of the Zobes mine water is very similar. The dominant bacterial phylum in all samples is the Proteobacteria. Interestingly, the analysis of biofilm samples of Zobes revealed a different bacterial community compared to the respective mine water. Geobacter, a known Fe(III)-reducing and U(VI)-reducing bacterium, was found to be the dominating genus in the bacterial biofilm community. For the investigation of the archaeal diversity of the mine water a dataset of 33658 (Pöhla), 19184 (Schlema-Alberoda) and 11401 (Zobes) sequences was analysed. In all samples the archaeal sequences mainly represent the three classes of Methanobacteria, Thermoprotei and Methanomicrobia.