Completely dechlorinating of trichloroethene by a Dehalococcoides mccartyi-containing microbial consortium in the absence of cobalamin

Completely dechlorinating of trichloroethene (TCE) by Dehalococcoides mccartyi (D.mccartyi) is catalyzed by reductive dehalogenases (RDases) which possess cobalamin as the crucial cofactor, whereas virtually all pure D.mccartyi strains isolated thus far are corrinoid auxotrophs. Exogenous addition of commercially available cobalamin for real TCE-contaminated site decontamination is deemed to be unrealistic. In this study, TCE reduction by a D.mccartyi-containing microbial consortium utilizing biosynthetic cobalamin generated by interior corrinoid-producing organisms within this mixed consortia was studied. The results confirmed that subcultures with exogenous cobalamin omitting from the medium apparently were impervious and enabled to successively metabolize TCE to non-chlorinated ethene. The 2-bromoethanesulfonate and ampicillin resistance tests results suggested that bacteria (particularly certain ampicillin-sensitive ones) rather than methanogenic archaea within this microbial consortium were responsible for biosynthesizing cobalamin. Moreover, relative stable Ɛ-carbon values of TCE among treatments in disregard of whether exogenous cobalamin or selective inhibitors were existed in the medium also speculated that cobalamin biosynthesized by these organisms was enable to uptake and utilize by D.mccartyi for RDases synthesis and eventually participated in TCE reduction. Finally, the Illumina MiSeq sequencing analysis indicated that Desulfitobacterium and Acetobacterium in this microbial consortium probably both were in charge of de novo cobalamin biosynthesis to fulfillment the requirements of D.mccartyi for TCE metabolism.

In situ pilot application of nZVI embedded in activated carbon for remediation of chlorinated ethene-contaminated groundwater: effect on microbial communities

Background Nanoscale zero-valent iron (nZVI) is commonly used for remediation of groundwater contaminated by chlorinated ethenes (CEs); however, its long-term reactivity and subsurface transport are limited. A novel nZVI–AC material, consisting of colloidal activated carbon (AC) with embedded nZVI clusters, was developed with the aim of overcoming the limitations of nZVI alone. Results Application of a limited amount of nZVI–AC to an oxic, nitrate-rich, highly permeable quaternary aquifer triggered time-limited transformation of CEs, with noticeable involvement of reductive dechlorination. Reductive dechlorination of CEs was dominantly abiotic, as an increase in the concentration of vinyl chloride (VC) and ethene did not coincide with an increase in the abundance of reductive biomarkers for complete dechlorination of CEs (Dehalococcoides, Dehalogenimonas, VC reductase genes vcrA and bvcA). Application of nZVI–AC under unfavourable hydrochemical conditions resulted in no dramatic change in the microbial community, the reducing effect resulting in temporal proliferation of nitrate and iron reducers only. At a later stage, generation of reduced iron induced an increase in iron-oxidizing bacteria. High concentrations and a continuous mass influx of competing electron acceptors (nitrate and dissolved oxygen) created unfavourable conditions for sulphate-reducers and organohalide-respiring bacteria, though it allowed the survival of aerobic microorganisms of the genera Pseudomonas, Polaromonas and Rhodoferax, known for their ability to assimilate VC or cis-1,2-dichloroethene. A potential for aerobic oxidative degradation of CE metabolites was also indicated by detection of the ethenotroph functional gene etnE. Conclusions This pilot study, based on the application of nZVI–AC, failed to provide a sustainable effect on CE contamination; however, it provided valuable insights into induced hydrogeochemical and microbial processes that could help in designing full-scale applications.