In situ TCE degradation mediated by complex dehalorespiring communities during biostimulation processes

The bioremediation of chloroethenes contaminants in groundwater polluted systems is always today a serious environmental challenge. Many previous studies have shown that cooperation of several dechlorinators is crucial for complete dechlorination of TCE (trichloroethene) to ethene. In the present study, we used an explorative functional DNA microarray (DechloArray) to examine the composition of specific functional gene in groundwater samples in which the chloroethene bioremediation was enhanced by delivery of hydrogen-releasing compounds. Our results demonstrate for the first time that complete biodegradation occurs through spatial and temporal variations of a wide diversity of dehalorespiring populations involving both Sulfurospirillum, Dehalobacter, Desulfitobacterium, Geobacter and Dehalococcoides genera. Sulfurospirillum appears the most active in the highly contaminated source zone, while Geobacter was only detected in the slightly contaminated downstream zone. The concomitant detection of both bvcA and vcrA genes suggests that at least two different Dehalococcoides species are probably responsible for the dechlorination of DCE and VC to ethene. These species were not detected on sites where cis-DCE accumulation was observed. These results support the notion that monitoring dechlorinators by the presence of specific functional biomarkers using a powerful tool such as DechloArray will be useful to survey the efficiency of bioremediation strategies.