title: Dechlorination of three tetrachlorobenzene isomers by contaminated harbor sludge-derived enrichment cultures follows thermodynamically favorable reactions.
abstract: Dechlorination patterns of three tetrachlorobenzene isomers, 1,2,3,4-, 1,2,3,5-, and 1,2,4,5-TeCB, were studied in anoxic microcosms derived from contaminated harbor sludge. The removal of doubly, singly, and un-flanked chlorine atoms was noted in 1,2,3,4- and 1,2,3,5-TeCB fed microcosms, whereas only singly flanked chlorine was removed in 1,2,4,5-TeCB microcosms. The thermodynamically more favorable reactions were selectively followed by the enriched cultures with di- and/or mono-chlorobenzene as the main end products of the reductive dechlorination of all three isomers. Based on quantitative PCR analysis targeting 16S rRNA genes of known organohalide-respiring bacteria, the growth of Dehalococcoides was found to be associated with the reductive dechlorination of all three isomers, while growth of Dehalobacter, another known TeCB dechlorinator, was only observed in one 1,2,3,5-TeCB enriched microcosm among biological triplicates. Numbers of Desulfitobacterium and Geobacter as facultative dechlorinators were rather stable suggesting that they were not (directly) involved in the observed TeCB dechlorination. Bacterial community profiling suggested bacteria belonging to the phylum Bacteroidetes and the order Clostridiales as well as sulfate-reducing members of the class Deltaproteobacteria as putative stimulating guilds that provide electron donor and/or organic cofactors to fastidious dechlorinators. Our results provide a better understanding of thermodynamically preferred TeCB dechlorinating pathways in harbor environments and microbial guilds enriched and active in anoxic TeCB dechlorinating microcosms.
authors.affiliation: Laboratory of Microbiology, Wageningen University, Wageningen, The Netherlands.|College of Environmental Science and Engineering, Hunan University, Changsha, People's Republic of China.
authors.forename: Yue
authors.initials: Y
authors.lastname: Lu
authors.affiliation: Laboratory of Microbiology, Wageningen University, Wageningen, The Netherlands.|Laboratory of Systems and Synthetic Biology, Wageningen University, Wageningen, The Netherlands.
authors.forename: Javier
authors.initials: J
authors.lastname: Ramiro-Garcia
authors.affiliation: Division of Soil and Water Management, KU Leuven, Leuven, Belgium.
authors.forename: Pieter
authors.initials: P
authors.lastname: Vandermeeren
authors.affiliation: Division of Soil and Water Management, KU Leuven, Leuven, Belgium.
authors.forename: Steffi
authors.initials: S
authors.lastname: Herrmann
authors.affiliation: Division of Soil and Water Management, KU Leuven, Leuven, Belgium.
authors.forename: Danuta
authors.initials: D
authors.lastname: Cichocka
authors.affiliation: Division of Soil and Water Management, KU Leuven, Leuven, Belgium.
authors.forename: Dirk
authors.initials: D
authors.lastname: Springael
authors.affiliation: Laboratory of Microbiology, Wageningen University, Wageningen, The Netherlands.
authors.forename: Siavash
authors.initials: S
authors.lastname: Atashgahi
authors.affiliation: Laboratory of Microbiology, Wageningen University, Wageningen, The Netherlands. hauke.smidt@wur.nl.
authors.forename: Hauke
authors.initials: H
authors.lastname: Smidt
mesh_terms: D001673:Biodegradation, Environmental; D002713:Chlorine / Q000302:isolation & purification / Q000378:metabolism*; D002722:Chlorobenzenes / Q000302:isolation & purification / Q000378:metabolism*; D041862:Chloroflexi / Q000235:genetics / Q000378:metabolism; D004269:DNA, Bacterial / Q000235:genetics*; D045858:Desulfitobacterium / Q000235:genetics / Q000378:metabolism; D045302:Geobacter / Q000235:genetics / Q000378:metabolism; D006801:Humans; D059013:Microbial Consortia / Q000235:genetics*; D010459:Peptococcaceae / Q000235:genetics / Q000378:metabolism; D012722:Sewage / Q000737:chemistry / Q000382:microbiology*; D013237:Stereoisomerism; D013816:Thermodynamics; D014874:Water Pollutants, Chemical / Q000302:isolation & purification / Q000378:metabolism*
chemical_list: D002722:Chlorobenzenes; D004269:DNA, Bacterial; D012722:Sewage; D014874:Water Pollutants, Chemical; D002713:Chlorine; C030386:1,2,3,4-tetrachlorobenzene
keywords: Dehalobacter; Dehalococcoides mccartyi; Organohalide respiration; Tetrachlorobenzenes; Thermodynamically favorable reactions