In situ TCE degradation mediated by complex dehalorespiring communities during biostimulation processes.
Bottom Line: 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.These species were not detected on sites where cis-dichloroethene 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 for surveying the efficiency of bioremediation strategies.
Affiliation: Clermont Université, Université Blaise Pascal, Laboratoire Microorganismes: Génome et Environnement, BP 10448, F63000, Clermont-Ferrand, France.Show MeSH
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Mentions: The RDA showed that variation in the detection of genes involved in dechlorination could be explained by different geochemical parameters (P ≥ 0.05). The first principal canonical axis (F1) accounted for 51.25% of the variation; together with the second canonical axis (F2), this value increased to 70.15% (Fig. 4). On the basis of the sample distribution on the F1 and F2 axis, three sectors were identified. In the first sector (Group A), high TCE concentrations were positively correlated with Sulfurospirillum and Dehalobacter/Desulfitobacterium pceA genes that encode enzymes responsible for the reduction of both PCE and TCE to cis‐DCE (Neumann et al., 1998; Maillard et al., 2003) and that were identified in all samples not perturbed by lactate injections collected at the source zone P2 (sampling periods C1, C3 and C5). In contrast, in the second sector (Group B), the three samples unaffected by lactate injections from the plume well P3 (sampling periods C1, C3 and C5), and those from the plume well P4 were associated with high VC, ethene and methane concentrations and showed positive correlation with the detection of VC‐reductase genes vcrA and bvcA. The genes encoding putative RDases (rdhA1a, rdhA1b and rdhA2a) with orthologues in several Dehalococcoides genomes (Table S1) were also associated with this group. Finally, this group showed a strong negative correlation with ORP, sulfate and nitrate concentrations. The sporadic detection of pceA from Geobacter species in well P4 could suggest its importance in the removal of traces of TCE remaining in this plume. The last section (Group C) grouped all samples for which no or few degradation abilities were detected: P1 samples and those from P2 and P3 affected by lactate injections (sampling periods C2 and C4). This last group was also positively correlated with high sulfate and nitrate concentrations. This highlights that environmental parameters, particularly electron acceptors (nitrate, sulphate, TCE, cis‐DCE or VC) and reductive conditions (ORP, methanogenesis), could control the spatial and temporal establishment of key microbial populations involved in the biodegradation process during the bioremediation treatment. In addition, functional gene patterns identified in each sample appeared to be closely related with the degradation reactions occurring in the nearby area, suggesting that these fingerprints could serve as indicator of site conditions and allow optimizing microbial activity for improved bioremediation processes.
Affiliation: Clermont Université, Université Blaise Pascal, Laboratoire Microorganismes: Génome et Environnement, BP 10448, F63000, Clermont-Ferrand, France.