Microorganisms in saline environments

The long-term safety of nuclear waste in deep geological repositories is an important issue in the German society. The migration of actinides and long-lived fission products within the respective host rock and the transport behaviour after a possible release from the repository should be well known. Presence of microorganisms was shown in the subsurface geologic layers, including salt formations, which are considered as potential host rocks /1/. This is of interest because microbes can affect physical and geochemical conditions (e.g. pH, Eh, release of gases) on site and they can also interact with actinides. Important interaction processes are biosorption, bioaccumulation, biotransformation, biomineralization and microbial enhanced chemisorption /2/.
In this work microbial communities were investigated in two different saline environments - the Arava desert in Israel and the salt formation near Gorleben village in Germany.

DESCRIPTION OF THE WORK

Total DNA was recovered from the salt crust (7EY) and from 0 to 3cm depth (10EY) samples of the Arava desert and from one hydrocarbon rich sample C1 from the Gorleben site. Direct molecular analyses of prokaryotic communities were performed by using bacteria specific 16S rRNA gene primers 27F and 1513R /3/ and archaea specific 16S rRNA gene primers 21F and 968R /4/.
Modified R2A medium was used for cultivation of halophilic microbial isolates as described in /5/.

RESULTS

It was demonstrated that the archaeal communities in both 7EY and 10EY samples were predominated by Halobacteriaceae /4/. The recently actualized affiliation of the 16S rRNA gene sequences demonstrated presence of representatives of the genera Haloplanus, Natronomonas, Halobacterium and Halolamina. Several haloarchaeal isolates were cultivated from the salt crust sample 7EY and one of them was characterized as Halobacterium sp. UJ-EY-1 /5/.
On the bacterial phylum level, the samples 7EY and 10EY were predominated by Bacteroidetes, which were accompanied by Firmicutes, Gamma-, Alpha-, and Delta-proteobacteria occurring in a sample-specific way. In addition, differences were found on the species level.
Preliminary results demonstrate that Bacteroidetes are rather abundant in the Gorleben sample C1 where, in addition, Firmicutes are also predominant. Different Proteobacteria are identified in this sample as well. Further investigations of microbial diversity in this and other samples from the Gorleben site are in progress.

At this step of investigation characterization of microbial communities in salt formations representative for potential nuclear waste disposals is ongoing. The next step will be to understand the microbe-actinide interactions of the salt-specific microorganisms. This knowledge will be used to take the microbial activity into account in evaluating the long-term safety of the repositories hosted in salt formations.

REFERENCES

1. Vreeland, R.H., Pisseli A.F., McDonnough, S., Meyers, S. Distribution of halophilic bacteria in a subsurface salt formations. Extremophiles 2, 321-331 (1998).
2. Lloyd, J. R., Macaskie, L. E.: Biochemical basis of microbe-radionuclide interactions. Interactions of Microorganisms with Radionuclides, eds Keith-Roach, M. J., Livens, F. R. Elsevier Science Ltd., 313-342 (2002).
3. Geissler, A., Selenska-Pobell, S.: Addition of U(VI) to a uranium mining waste sample and resulting changes in the indigenous bacterial community. Geobiology 3, 275-285 (2005).
4. Buchvarova, V., Jankowski, U., Flemming, K., Selenska-Pobell S. Halophilic archaeal populations in Arava Desert (Israel) as examined by using direct molecular and cultivation methods FZR-Report 511, p. 34 (2009).
5. Jankowski, U., Flemming, K., Selenska-Pobell, S. Characterization of a Halobacterium sp. isolate cultivated from samples collected from Arava Desert. FZR-Report 511, p. 35 (2009).