Characterization of an H2-utilizing enrichment culture that reductively dechlorinates tetrachloroethene to vinyl chloride and ethene in the absence of methanogenesis and acetogenesis

Abstract

We have been studying an anaerobic enrichment culture which, by using methanol as an electron donor, dechlorinates tetrachloroethene (PCE) to vinyl chloride and ethene. Our previous results indicated that H 2 was the direct electron donor for reductive dechlorination of PCE by the methanol-PCE culture. Most-probablenumber counts performed on this culture indicated low numbers (<10 4 /ml) of methanogens and PCE dechlorinators using methanol and high numbers (>10 6 /ml) of sulfidogens, methanol-utilizing acetogens, fermentative heterotrophs, and PCE dechlorinators using H 2. An anaerobic H 2-PCE enrichment culture was derived from a 10 ؊6 dilution of the methanol-PCE culture. This H 2-PCE culture used PCE at increasing rates over time when transferred to fresh medium and could be transferred indefinitely with H 2 as the electron donor for the PCE dechlorination, indicating that H 2-PCE can serve as an electron donor-acceptor pair for energy conservation and growth. Sustained PCE dechlorination by this culture was supported by supplementation with 0.05 mg of vitamin B 12 per liter, 25% (vol/vol) anaerobic digestor sludge supernatant, and 2 mM acetate, which presumably served as a carbon source. Neither methanol nor acetate could serve as an electron donor for dechlorination by the H 2-PCE culture, and it did not produce CH 4 or acetate from H 2-CO 2 or methanol, indicating the absence of methanogenic and acetogenic bacteria. Microscopic observations of the purified H 2-PCE culture showed only two major morphotypes: irregular cocci and small rods.

Isolation and characterization of Dehalococcoides sp. strain FL2, a trichloroethene (TCE)‐ and 1,2‐dichloroethene‐respiring anaerobe

“…A recent study by Hölscher et al (2004) demonstrated that multiple, non-identical reductive dehalogenase genes are common in Dehalococcoides, but their findings also suggested that strain-specific reductive dehalogenase genes exist. Strain 195 requires undefined additions for growth, and we tested the effects of filter-sterilized anaerobic digester sludge supernatant (Maymó-Gatell et al, 1995) used to grow strain 195 on dechlorination activity of strain FL2. Amended cultures performed similarly compared with cultures without additions suggesting that strain FL2 does not require unknown growth factors.…”

“…Filter-sterilized, anoxic anaerobic digester sludge supernatant required for growing D. ethenogenes strain 195 (Maymó-Gatell et al, 1995 was added to a final volume of 10% (v/v) to acetate, hydrogen and TCE-amended medium. Trichloroethene dechlorination was monitored and compared with control cultures that did not receive sludge supernatant.…”

Transcription and mass‐spectroscopic proteomic studies of electron transport oxidoreductases in Dehalococcoides ethenogenes

“…Tetrachloroethene and other chemicals were purchased and utilized as previously described (Maymo-Gatell et al, 1995). In short, quantitative chloroethene analyses of headspace gases (100 µl) in batch-pure cultures were analysed on a temperature-programmed Perkin-Elmer model 8500 gas chromatograph (GC) equipped with a flame ionization detector and type RTX-502.2 capillary column (Restek, Bellefonte, PA).…”

Performance of Full‐Scale Enhanced Reductive Dechlorination in Clay Till

“…The redox conditions in the source and plume were nitrate to iron reducing and no Dhc were detected in the groundwater. The conditions for complete reductive dechlorination to nontoxic compounds were not met at the site before remediation as the preferred conditions for reductive dechlorination are iron reducing to methanogenic (e.g., Hoelen and Reinhard 2004;MaymoGatell et al 1995;Wei and Finneran 2011) and Dhc are needed to carry out degradation beyond cis-DCE and VC (MaymoGatell et al 1997).…”