CHARACTERIZATION OF AN H-2-UTILIZING ENRICHMENT CULTURE THAT REDUCTIVELY DECHLORINATES TETRACHLOROETHENE TO VINYL-CHLORIDE AND ETHENE IN THE ABSENCE OF METHANOGENESIS AND ACETOGENESIS

We have been studying an anaerobic enrichment culture which, by using methanol as an electron donor, dechlorinates tetrachloroethene (PCE) t o vinyl chloride and ethene. Our previous results indicated that H-2 w as the direct electron donor for reductive dechlorination of PCE by th e methanol-PCE culture. Most-probable number counts performed on this culture indicated low numbers (less than or equal to 10(4)/ml) of meth anogens and PCE dechlorinators using methanol and high numbers (greate r than or equal to 10(6)/ml) of sulfidogens, methanol-utilizing acetog ens, fermentative heterotrophs, and PCE dechlorinators using H-2. An a naerobic 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 increas ing rates over time when transferred to fresh medium and could be tran sferred indefinitely with H-2 as the electron donor for the PCE dechlo rination, indicating that H-2-PCE can serve as an electron donor-accep tor pair for energy conservation and growth. Sustained PCE dechlorinat ion by this culture was supported by supplementation with 0.05 mg of v itamin B-12 per liter, 25% (vol/vol) anaerobic digestor sludge superna tant, and 2 mM acetate, which presumably served as a carbon source. Ne ither methanol nor acetate could serve as an electron donor for dechlo rination by the H-2-PCE culture, and it did not produce CH4 or acetate from H-2-CO2 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 r ods.