Characterization Studies of an Anaerobic, Pentachlorophenol-Dechlorinating Enrichment Culture

Abstract

Dechlorination studies were conducted using microbial cultures developed in a fluidized-bed reactor (FBR) that dechlorinates pentachlorophenol (PCP) to 3,4-dichlorophenol (3,4-DCP) and 4-monochlorophenol (4-MCP). Electron donor experiments demonstrated that lactate, propionate, and H2 can serve as electron donors for chlorophenol (CP) dechlorination in mixed, anaerobic, PCP-enriched cultures. Dechlorination did not proceed in the absence of an electron donor. Acetate, which resulted in little H2 production, was a poor electron donor. The results of inhibition studies using vancomycin and 2-bromoethanesulfonic acid implicate members of the domain bacteria in the dechlorination of CPs, whereas methanogens do not appear to be involved in dechlorination. Brief heat treatment (80°C for 90 min) of the FBR enrichment cultures implicated endospore formers in the dechlorination of CPs, primarily at the ortho position, where PCP was dechlorinated to 3,4,5-trichlorophenol (3,4,5-TCP) (the sole TCP detected) and subsequently to 3,4-DCP. Both lactate and H2 served as electron donors in the heat-and oxygen-treated cultures. In contrast, a lactate-fed anaerobic spread-plate enrichment culture exhibited solely meta-dechlorination, where PCP dechlorinated solely to 2,4,6-TCP. The separation of ortho- and meta-specific dechlorination reactions provides evidence that PCP dechlorination in the FBR enrichment culture was catalyzed by at least the following two separate groups of CP-dechlorinating bacteria: one meta-dechlorinating group and one primarily ortho-dechlorinating group.