Cold War Geomicrobiology

Microbial impacts on the fate of metals and radionuclides

The former mining site near Ronneburg immediately after remediation completed for the 2007 German national garden show (BUGA).

Tsing Bo Hu (doctoral student) sampling a core from the Gessenwiese test field site during a sampling trip in November 2011.

Uranium mining near Ronneburg, Germany during the Cold War Era resulted in significant, widespread environmental impacts at the mining site. Extensive remediation efforts began soon after the closing of the mines and, by focusing on massive physical remediation, i.e., the removal and stabilization of tons of impacted topsoil, the environmental legacy of mining in this area has mostly been erased. Nonetheless, groundwater is still contaminated with acid mine drainage (AMD) and heavy metals and poses a threat to nearby ecosystems. Microbial activity may limit the mobility of such contaminants through natural attenuation or bioremediation. Natural attenuation is any natural process that results in the reduction of contaminant concentrations in the environment through biological processes, physical phenomena, and chemical reactions. Bioremediation is the use of living organisms, e.g., plants, microbes, and fungi, to remove pollutants and typically aims to increase the activity of organisms via the addition of nutrients to an environment. In both cases, naturally occurring microorganisms, can immobilize contaminants via direct biological reduction (e.g., reduction of soluble U(VI) to insoluble U(IV)) or by indirect pathways (e.g., biogenic mineral precipitation). In addition, the conditions in some areas of our Ronneburg research site provide a unique opportunity for the study of microorganisms that can survive under atypically acidic, heavy-metal enriched, “extreme” conditions. The kinds of conditions we find at our research site have been shown at other locations to select for a community of microorganisms that can not only live, but even thrive in an environment that makes survival for most microorganisms exceedingly difficult.

Map of the Ronneburg area >>

Consequently, the Ronneburg area provides a unique opportunity within Germany to investigate microbe-mineral interactions by both extreme and “normal” microbial communities. It also allows us to look at shifts of microbial communities in relation to the changes in both the physical landscape and groundwater chemistry and at the potential for microbial activity to minimize contaminants migration. In our research program we are investigating microbe-metal interactions at two field sites in this area: (1) the Gessenwiese test field and (2) the Gessen Creek. The Gessenwiese test field is located on top of the former leaching heap, whereas the Gessen Creek is located downhill from the former mining site.

We are particularly interested in determining the structure and function of microbial communities at these sites and determining what impacts these microbial populations have on mineral formation (biomineralization). Iron- (Fe), sulfur-, and manganese- (Mn) bearing minerals are important sorbents for heavy metals and can impact dynamics of such contaminants. In the past our group focused on evaluating the role of reductive processes, catalyzed by Fe(III)-reducing bacteria (Dr. Eva-Maria Burkhardt’s Ph.D. thesis) and sulfate-reducing bacteria (Dr. Jana Sitte’s Ph.D. thesis) on mineral formation and metal mobility. Our work has now shifted to looking at the role of oxidative mineral formation processes on metal dynamics. Maria Fabisch’s Ph.D. thesis investigates how Fe(II)-oxidizing bacteria from the Gessen Creek impact metal dynamics, whereas, Tsing Bo Hu's Ph.D. thesis investigates the role of Mn(II)-oxidizing bacteria in mineral formation at the Gessenwiese test field. Carol Johnson (visting Ph.D. student) and Gina Freyer (master's student) are investigating transport of metals and nanoparticulate Fe oxides from upcoming mine water that is draining into the Gessen Creek via Fe seeps. We use a combination of microscopy, geochemical, and microbial community analytical techniques for our research. Microbial community analysis is performed by combining cultivation-dependent (i.e. anaerobic and microaerophilic) and cultivation-independent molecular techniques targeting SSU rRNA (i.e. PCR, cloning and sequencing, stable isotope probing (SIP), denaturing gradient gel electrophoresis (DGGE) and quantitative PCR). We use microscopy methods, such as Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) combined with energy-dispersive X-ray spectroscopy (EDS).