Dehalococcoides ethenogenes (DE), the only bacteria able to completely dechlorinate PCE to ethene, can be cultured for use in bioaugmentation of chlorinated solvent sites which lack the organism. Understanding the role of associated anaerobic microorganisms in providing critical metabolites for the healthy functioning of DE is important in culturing as well as assurring their survival in the subsurface. When DE was first isolated in pure culture in Zinder’s laboratory at Cornell University in 1995, it was determined that this organism can use only H2 as its source of energy, can utilize acetate as a carbon source, but requires vitamin B12 plus unidentified factors which are normally provided to the DE by other types of microorganisms which must be present with the DE under natural field conditions.
We describe the role of each critical organism in a DE mixed culture, and present results to support their role in maintaining the dechlorinating ability of DE. For example, since oxygen is toxic to DE, a very low redox is required, on the order of –200 mv. To achieve this redox potential, sulfate-reducing bacteria or methanogens must be stimulated to grow by addition of selected electron donors. In addition to lowering the redox potential, some strains of SRB and methanogens produce microbial growth factors such as vitamins B12. Other important members of the supporting consortium are acetogens and fermenting bacteria which produce the H2 needed by DE.
BCI’s bioaugmentation culture is a natural consortium containing DE as well as acetogens, methanogens, and sulfate-reducers, and can be maintained indefinitely in most groundwaters when amended with sodium lactate, ammonia, phosphate, sulfate, vitamin B12 and yeast extract. For some groundwaters, trace elements or additional trace organics are needed. We will provide results from microcosm and field projects demonstrating the importance of DE’s supporting bacteria.