Diversity of dechlorination pathways and organohalide respiring bacteria in chlorobenzene dechlorinating enrichment cultures originating from river sludge

Abstract

Anaerobic reductive dechlorination of hexachlorobenzene (HCB) and three isomers of tetrachlorobenzene (TeCB) (1,2,3,4-, 1,2,3,5- and 1,2,4,5-TeCB) was investigated in microcosms containing chloroaromatic contaminated river sediment. All chlorobenzenes were dechlorinated to dichlorobenzene (DCB) or monochlorobenzene. From the sediment, a methanogenic sediment-free culture was obtained which dechlorinated HCB, pentachlorobenzene, three TeCB isomers, three trichlorobenzene (TCB) isomers (1,2,3-, 1,2,4- and 1,3,5-TCB) and 1,2-DCB. Dechlorination involved multiple pathways including the removal of doubly flanked, singly flanked and isolated chlorine substituents. 454-pyrosequencing of partial bacterial 16S rRNA genes amplified from selected chlorobenzene dechlorinating sediment-free enrichment cultures revealed the presence of a variety of bacterial species, including Dehalobacter and Dehalococcoides mccartyi, that were previously documented as organohalide respiring bacteria. A genus with apparent close relationship to Desulfitobacterium that also has been associated with organohalide respiration, composed the major fraction of the operational taxonomic units (OTUs). Another major OTU was linked with Sedimentibacter sp., a genus that was previously identified in strict co-cultures of consortia reductively dehalogenating chlorinated compounds. Our data point towards the existence of multiple interactions within highly chlorinated benzene dechlorinating communities.

Characterization of a Highly Enriched Microbial Consortium Reductively Dechlorinating 2,3-Dichlorophenol and 2,4,6-Trichlorophenol and the Corresponding cprA Genes from River Sediment

“…These investigations were made possible using laboratory microcosms. Anaerobic reductive dechlorination of chlorinated benzenes for example was investigated in microcosms containing chloroaromatic-contaminated river sediment (Vandermeeren et al, 2014). Dechlorination activity in enrichment cultures showed at least three different dechlorination reactions.…”

“…The dechlorination of pentachlorophenols was detected in the sludge from a pulp and paper mill (Karn et al, 2011). Reductive dechlorination of CPs, biphenyls, and benzenes has been reported in a number of sedimentary environments (Wu et al, 1998;Fagervold et al, 2005;Zanaroli et al, 2010;Kjellerup et al, 2014;Kuokkaa et al, 2014;Vandermeeren et al, 2014).…”

Ecophysiology and environmental distribution of organohalide-respiring bacteria

“…All samples were collected in September 2008, and stored for three months at 4°C until they were used in this study. The microcosms were set up as described elsewhere [340] with 10 g of sludge and 40 ml of an anoxic medium [52], and 20 mM lactate as electron To study the dynamics of degradation pathways and microbial communities, and to obtain sediment-free TeCB-enriched cultures, serial transfers were performed. A 5% inoculum from the original TeCB-fed microcosms was transferred into fresh anoxic bottles containing growth medium, fed with 50 µM of the same TeCB isomer as the initial inoculum and cultivated for 66 days (Figure 5.1, step 4).…”

“…TeCBs can be anaerobically biotransformated following diverse pathways [8,338]. Preference for thermodynamically more favorable CB dechlorination pathways was shown before in an anaerobic microbial consortium originating from lake sediment [339], but this selectivity was not observed in other microcosms derived from contaminated freshwater sediments [336,340]. Currently known bacterial isolates able to dechlorinate TeCB isomers belong to Dehalococcoides mccartyi in the phylum Chloroflexi [159,335] and Dehalobacter in the phylum Firmicutes [57].…”

“…Bacteria of the genus Geobacter were found associated with HCB dechlorination in an anaerobic consortium originating from contaminated river sediment as determined by genus-specific quantitative PCR (qPCR), suggesting they also may serve as CB dechlorinators [336]. Furthermore, a recently reported bacterial community analysis with 454 pyrosequencing of 16S ribosomal RNA (rRNA) gene fragments conducted on a range of anaerobic CB-dechlorinating enrichments from contaminated river sludge revealed a high relative abundance (21.38 % -55.07%) of populations closely related to Desulfitobacterium, while Dehalococcoides and Dehalobacter together represented less than 0.53% of the bacterial community [340].…”