Chloroethenes are hazardous environmental pollutants frequently detected in groundwater and soil. Natural occurring microbial degradation processes of chloroethenes are known to be limited by the availability of electron donors (e.g. H₂) and acceptors (e.g. O₂). In recent years, electrode applications were increasingly considered to stimulate microbial remediation processes. The aim of the project at the TZW is to use electrodes to enhance microbial degradation of chloroethenes via water electrolysis. The electrochemical formation of hydrogen and oxygen will be used to generate zones favourable for microbial dechlorination.

In general, understanding the effects of electric currents and electrochemical reactions on microorganisms is a pre-requisite for successful electro-bio-processes development. Therefore, the dynamic changes in a VC dechlorinating enrichment culture were investigated during exposure to an electric field and subsequent incubation, applying DNA analysis by denaturating gradient gel electrophoresis (DGGE).

A vinylchloride (VC) dechlorinating enrichment culture was exposed to an electric field and samples were taken for activity and DGGE analysis. After DGGE analysis, a major distinctive DNA band could be seen in all samples which presumably represents the VC dechlorinating organism. Dechlorination activity could be correlated to band thickness. In samples showing microbial dechlorinating activity the bands were more dominant indicating that more DNA was present in these samples due to microbial growth.

In summary no shift in bands could be detected in the enrichment culture throughout the incubation period and along the electrolysis. The dechlorinating activity correlated with DNA band thickness and decreased with increasing exposure to the electric field. Inhibiting effects were only observed at very high current intensities (I = 350mA, Electrode area = 20 cm², Volume: 900 mL) and additional chemical analysis revealed that these effects were due to the electrochemical formation of toxic by-products rather than directly related to the electric field. Furthermore, at electric field intensities required for field conditions no effects on microorganism activity could be observed.

The same experimental procedure can be applied to study the sensitivity of different bacteria to electric fields and electrochemical reactions. The bands of interest have been cut out from the DGGE gels and the DNA was amplified using PCR in preparation for sequencing. This will allow the identification of relevant bacterial species present in the enrichment cultures.

Acknowlegdment: The authors gratefully acknowledge financial support by the COST office, AIF Otto von Guericke, EPSRC, BUCKINGHAM Group Contracting and FIRST FARADAY.

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