Retrieval and Biodiversity of Biofilms of an Underground Uranium Mine

Acid mine drainages (AMD) result from in-situ leaching with sulfuric acids. These acidic waters in the underground of the former uranium mine Königstein (Saxony, Germany) are characterized by high concentrations of metals (U, Fe) and sulfate (low pH) and flow through the sandstone. Biofilms grow in this unique subsurface habitat (250 meters below ground) either as stalactite-like slime communities (snotites) or as acid streamers in the drainage channels. Previously conducted studies on the bacterial diversity in both biofilm communities showed that beta-proteobacterium affiliated with Ferrovum myxofaciens, also designated “Ferribacter polymyxa” were identified as dominating bacterial species.
Biofilms are not only composed of bacteria, but may also include eukaryotic organisms. The eukaryotic diversity of the Königstein biofilms was analysed by molecular methods, i.e. 18S rDNA PCR, cloning and sequencing, which were used to determine the DNA-fragments of the microorganism, and by microscopic investigations. It was found that the eukaryotic biofilm communities of the Königstein environment showed a limited number of different heterotrophic species and consist of a variety of lineages belonging to nine major taxa: Ciliates, Flagellates, Amoebae, Heterolobosea, Fungi, Apicomplexa, Stramenopiles, Rotifers and Arthropoda and in addition a large number of uncultured eukaryotes, denoted as acidophilic eukaryotic cluster (AEC). Since 2010 the Königstein mine was flooded, and the galleries are no longer accessible for sampling. Biofilm analyses are now possible by pumping the flooding water from underground to the surface, through biofilm sampling devices, e.g. biofilm reactors. The In-situ Biofilm reactor (165 cm in length and 39 cm in diameter) included biofilm carriers where water microorganisms are attached to the carrier surface, indicated by the brown and slimy appearance. Biofilms on the carriers were used for different investigations e.g. CARD-FISH and pyrosequencing for determine the biodiversity after flooding.