Insights into the Biodiversity of salt sumps in the Asse II salt mine, Germany

The former salt mine (1908-1964) Asse II, Germany is a final disposal site of radioactive waste. It is composed of salt rocks, which are approximately 250 million years old. A number of salt sumps exist in the Asse II, which were so far not microbiologically characterized. In this study, cultivation-independent methods, e.g. pyrosequencing, were applied to identify the microbial diversity in these unique salt sump habitats.
In this study, a total of 3.168 sequences, divided in 314 operational taxonomic units (OTUs), representing bacterial and archaeal groups from the underground Asse II salt mine. The class halobacteria (Euryarchaeota) predominates the archaeal community, representing 99.5% of all sequences. The least abundant sequences were represented by Thermoprotei (Crenarchaeota) and Methanobacteria (Euryarchaeota).
In addition, halophilic bacteria have been detected in the salt sumps of the underground Asse II mine. A total of 8 phyla of bacteria were identified by 16S rRNA sequence analyzes. The dominating phylum are Firmicutes (e.g. Bacilli, Halocella, Filifactor, Veillonella) with ~51% of all detected bacterial sequences, followed by Proteobacteria (Marinobacter, Hyphomicrobium, Methylophilus, Pseudomonas, Sphingomonas) with ~19%.
This study identified for the first time extreme halophilic bacteria and archaea in the underground salt sumps of the Asse II environment. For generating a final disposal site, not only geological, chemical or physical, but also microbiological aspects are important to consider.