Description:
<jats:title>Abstract</jats:title><jats:p>2,4,6‐Trichlorophenol (2,4,6‐TCP) was extensively used in the past as a component of various pesticide formulations as well as a wood preservative and, therefore, is ubiquitously present in the environment. It is also formed during the disinfection of drinking water sources or during wastewater treatment and is frequently detected in sewage sludges. Under anaerobic conditions, reductive dehalogenation is the most promising biological process for its detoxification. Here, an anaerobic, 2,4,6‐TCP <jats:italic>ortho</jats:italic>‐dehalogenating mixed culture is described, which was originally enriched from a Saale river sediment. In order to be able to analyze the capacity of this dechlorination process for the removal of 2,4,6‐TCP, a steady‐state continuous culture was grown over a period of 270 days under an N<jats:sub>2</jats:sub>‐CO<jats:sub>2</jats:sub> (80:20) gas atmosphere in a chemostat using formate as an electron donor and 2,4,6‐trichlorophenol (2,4,6‐TCP) as an electron acceptor. 2,4,6‐TCP was dechlorinated via 2,4‐dichlorophenol (2,4‐DCP) to 4‐chlorophenol (4‐CP) liberating two chlorine atoms per molecule of 2,4,6‐TCP as chloride. Per mol of chloride, 2.2 mol of formate were consumed and 0.17 mol of acetate formed. When yeast extract (0.01 %) was omitted from the cultivation medium, 2,4‐DCP accumulated in the chemostat, suggesting that the components in the yeast extract were essential for reductive dechlorination. A second fermentation was performed over a period of 130 days in the absence of CO<jats:sub>2</jats:sub> in the gas atmosphere and of carbonate in the cultivation medium, resulting in a slightly higher specific dechlorination rate, a higher requirement for formate, and a lower protein yield, indicating that formate was used as a sole carbon source for growth. The dilution rate (<jats:italic>D</jats:italic>) was continuously increased, leading to an increase of the dechlorination velocity up to 400 μmol Cl<jats:sup>–</jats:sup>/L h, a maximum specific dechlorination rate of 0.48 μmol Cl<jats:sup>–</jats:sup>/L min (mg protein) and a yield of 5.1 g protein/(mol Cl<jats:sup>–</jats:sup> released). The microbial community structure of the mixed culture was investigated by amplified ribosomal DNA restriction analysis (ARDRA), sequencing, and hybridization with species specific oligonucleotide probes. The dechlorinating bacterium <jats:italic>Desulfitobacterium hafniense</jats:italic> was found to be a dominant member of the mixed chemostat culture. Further members of the chemostat culture were detected by comparative analysis of the restriction patterns and sequencing and identified as bacteria most closely related to strains of <jats:italic>Sedimentibacter, Clostridium propionicum,</jats:italic> and <jats:italic>Pseudomonas aeruginosa</jats:italic>.</jats:p>