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.Electronic supplementary materialThe online version of this article (doi:10.1007/s00253-016-8004-8) contains supplementary material, which is available to authorized users.

Organohalide respiration in pristine environments: implications for the natural halogen cycle

“…Five isolates were obtained from marine and estuary sediments (Table 2) not reported to be exposed to anthropogenic organohalogens. However, complete lack of encounter with anthropogenic organohalogens cannot be excluded, especially in coastal harbours commonly reported to be contaminated with organohalogens (Kengen et al, 1999;Lu et al, 2017). An exceptional example is Desulfoluna spongiiphila strain AA1 isolated from marine sponges known to produce a variety of organobromines (Ahn et al, 2009).…”

Organohalide-respiringDesulfolunaspecies isolated from marine environments

“…Such a natural and ancient presence of organohalogens in marine environments may have primed development of various microbial dehalogenation metabolisms [6]. Furthermore, marine environments and coastal regions in particular are also commonly reported to be contaminated with organohalogens from anthropogenic sources [7].…”

NG-Tax, a highly accurate and validated pipeline for analysis of 16S rRNA amplicons from complex biomes

“…Lowering the threshold will lead to the acceptance of low abundant OTUs, with an increased probability of these OTUs being artifacts due to sequencing and PCR errors. Abundance thresholds are commonly used to remove spurious OTUs generated by sequencing and PCR errors 8,36 , but previous studies applied a fraction threshold defined by the complete dataset under study, thereby ignoring sample size heterogeneity which may lead to under-representation of asymmetrically distributed OTUs.…”

“…using different approaches and drawing the same biological conclusions) cannot be attained. This is an alarming observation since studies are often used to identity biomarker organisms, associated with certain host phenotypes (often comparing a diseased state to a healthy state), yet the use of different primers might show different biomarkers 8,22,23,27,28,30 . So far, neither currently available pipelines nor taxonomic classifiers have been able to efficiently reduce the noise in this type of data.…”

“…Reproducibility can be evaluated by comparing separate sequencing runs and different primer pairs that cover distinct 16S rRNA gene regions. Although replicability is often achieved, accuracy has been shown to be challenging especially at higher taxonomic resolution such as at genus level 8,9 .…”