Bacterial Cultures Preferentially Removing Singly Flanked Chlorine Substituents from Chlorobenzenes

Abstract

The wide though not ubiquitous distribution of chlorobenzene-dechlorinating bacteria in anaerobic sludge from German sewage plants is demonstrated. The model substrates 1,2,3- and 1,2,4-trichlorobenzene (TCB) were dechlorinated to dichlorobenzenes (DCBs) and monochlorobenzene (MCB) via distinct pathways. For easy visualization and differentiation of the pathways, a novel plotting method was developed. While many of the cultures showed a dechlorination pattern similar to that previously found for Dehalococcoides species, removing doubly flanked rather than singly flanked chlorine substituents from TCBs, some cultures formed 1,2-DCB from 1,2,3-TCB and/or 1,3-DCB from 1,2,4-TCB. Stable cultures preferentially catalyzing the removal of singly flanked chlorines were obtained by repeated subcultivation in sediment-free synthetic medium. This dechlorination pattern is potentially of great benefit for remediation as the accumulation of persistent intermediates such as 1,3,5-TCB from highly chlorinated compounds can be avoided. In addition, the cultures dechlorinated 1,3,5-TCB, pentachlorobenzene (PeCB), and hexachlorobenzene (HCB). Nested PCR demonstrated the presence of low numbers of Dehalococcoides species. However, the observed insensitivity of the dechlorinating bacteria in our cultures to oxygen and sensitivity to vancomycin is not in accordance with the reported properties of Dehalococcoides species, suggesting that other bacteria than Dehalococcoides catalyzed the removal of singly flanked chlorines from TCB.

Dehalogenation of Chlorobenzenes, Dichlorotoluenes, and Tetrachloroethene by Three Dehalobacter spp.

“…1,3,5-TCB is the product of dehalogenation of HCB or QCB by organisms with a preference for doubly flanked chlorines, and has been detected as an end-product in several mixed cultures ,, and pure cultures containing Dehalococcoides spp. and relatives. ,, Dehalogenation of 1,3,5-TCB to 1,3-DCB and MCB has been observed before in mixed communities, − but a causative organism has not been identified. Dehalobacter sp.…”

“…strain 13DCB1 dehalogenated 1,3,5-TCB to MCB with little detectable buildup of 1,3-DCB, consistent with its ability to use meta-substituted chlorines, and qPCR studies indicated this dehalogenation supported its growth (Figure B). This pattern for 1,3,5-TCB utilization is different from that described for an enrichment culture in which there was significant buildup of 1,3-DCB and no MCB. More recently, enrichments from Vietnam sediments were shown to dechlorinate 1,3,5-TCB to MCB, but 1,3-DCB accumulated as an intermediate, suggesting mechanistic differences.…”

Reductive Dehalogenation of Oligocyclic Phenolic Bromoaromatics by Dehalococcoides mccartyi Strain CBDB1

“…Many studies have been carried out with Dehalococcoides strains on the transformation of simply structured organohalides such as chlorinated benzenes, , phenols, ethenes, − ethanes, and propanes, among others. Dehalococcoides strains were also able to dehalogenate di- and tricyclic aromatic compounds such as polychlorinated biphenyls, − chlorinated dioxins, − or brominated diphenyl ethers .…”

“…15−18 Reductive dehalogenase homologous genes (rdh genes) are particularly abundant in Dehalococcoides species with 10−36 copies in the known D. mccartyi genomes. 19 Many studies have been carried out with Dehalococcoides strains on the transformation of simply structured organohalides such as chlorinated benzenes, 20,21 phenols, 22 ethenes, 23−25 ethanes, 26 and propanes, 27 among others. Dehalococcoides strains were also able to dehalogenate di-and tricyclic aromatic compounds such as polychlorinated biphenyls, 28−30 chlorinated dioxins, 31−33 or brominated diphenyl ethers.…”

Changes of the Proteome and Acetylome during Transition into the Stationary Phase in the Organohalide-Respiring Dehalococcoides mccartyi Strain CBDB1

“…D. mccartyi strain CBDB1 [6] was shown to reductively dehalogenate an exceptionally broad spectrum of halogenated, mostly aromatic, electron acceptors ranging from polychlorinated to -brominated benzenes (e.g., [7,8], polychlorinated dibenzo-p-dioxins [9], biphenyls [10], phenols [11], including bromophenol blue [12], and the herbicide 2,4,5-T [13]). Despite its slow growth, with doubling times between 1 and 3 days [14], D. mccartyi is a key organism for the bioremediation of groundwater and soil contaminated with organohalides [15].…”