Anaerobic transformation and toxicity of trichlorophenols in a stable enrichment culture

The transformation and toxicity of trichlorophenols (TCPs) were studied with a methanogenic enrichment culture derived from sewage sludge. Transformation of TCPs rapidly resumed after heating of the culture at 80°C for 1 h, suggesting that the dechlorinating bacteria are spore-forming anaerobes. 2,4,6-TCP was rapidly dechlorinated via 2,4-dichlorophenol to 4- chlorophenol. During the transformation of 2,4,6-TCP, the most probable number of dechlorinating bacteria increased by 4 orders of magnitude. The most extensive dechlorination was observed in media with complex carbon sources such as yeast extract, peptone, and Casamino Acids, but glucose, galactose, and lactose were also used by the consortium. Experiments using chloramphenicol indicated that the reductive dechlorination of 2,4,6-TCP was regulated by an inducible enzyme system. The highest initial concentration at which dechlorination of 2,4,6-TCP was observed was 400 μM. 2,4,5-TCP and 3,4,5-TCP were dechlorinated to, respectively, 3,4-dichlorophenol and 3- chlorophenol at initial concentrations of ≤40 μM. Toxicity for the acid- producing and methanogenic bacteria in the consortium was a function of chemical structure, as the inhibition of these activities increased from 2,4,6-TCP, via 2,4,5-TCP, to 3,4,5-TCP.