Selective Enrichment Yields Robust Ethene-Producing Dechlorinating Cultures from Microcosms Stalled at cis-Dichloroethene

Abstract

Dehalococcoides mccartyi strains are of particular importance for bioremediation due to their unique capability of transforming perchloroethene (PCE) and trichloroethene (TCE) to non-toxic ethene, through the intermediates cis-dichloroethene (cis-DCE) and vinyl chloride (VC). Despite the widespread environmental distribution of Dehalococcoides, biostimulation sometimes fails to promote dechlorination beyond cis-DCE. In our study, microcosms established with garden soil and mangrove sediment also stalled at cis-DCE, albeit Dehalococcoides mccartyi containing the reductive dehalogenase genes tceA, vcrA and bvcA were detected in the soil/sediment inocula. Reductive dechlorination was not promoted beyond cis-DCE, even after multiple biostimulation events with fermentable substrates and a lengthy incubation. However, transfers from microcosms stalled at cis-DCE yielded dechlorination to ethene with subsequent enrichment cultures containing up to 109 Dehalococcoides mccartyi cells mL−1. Proteobacterial classes which dominated the soil/sediment communities became undetectable in the enrichments, and methanogenic activity drastically decreased after the transfers. We hypothesized that biostimulation of Dehalococcoides in the cis-DCE-stalled microcosms was impeded by other microbes present at higher abundances than Dehalococcoides and utilizing terminal electron acceptors from the soil/sediment, hence, outcompeting Dehalococcoides for H2. In support of this hypothesis, we show that garden soil and mangrove sediment microcosms bioaugmented with their respective cultures containing Dehalococcoides in high abundance were able to compete for H2 for reductive dechlorination from one biostimulation event and produced ethene with no obvious stall. Overall, our results provide an alternate explanation to consolidate conflicting observations on the ubiquity of Dehalococcoides mccartyi and occasional stalling of dechlorination at cis-DCE; thus, bringing a new perspective to better assess biological potential of different environments and to understand microbial interactions governing bioremediation.

Ozone enhances biodegradability of heavy hydrocarbons in soil

“…The soil used in this test had been treated with ozone for 2·5 h. Amplicon sequencing of the V4 region of the 16S ribosomal ribonucleic acid (rRNA) gene was performed using the barcoded primer set 515F/806R by Caporaso et al (Edgar, 2010). Singletons were removed and the OTU table was rarefied to the minimum number of sequences obtained among the samples (25 485 sequences) as previously described (Delgado et al, 2014b). Table 2.…”

Electron‐acceptor loadings affect chloroform dechlorination in a hydrogen‐based membrane biofilm reactor

“…The fibers were pressurized on both ends with H 2 (ultrahigh purity) at a pressure of 4 psig (1.27 atm total pressure). The inoculum was 30 ml of the Zara‐10 enrichment culture (Delgado et al, ). The anaerobic medium was adapted from Delgado, Parameswaran, Fajardo‐Williams, Halden, and Krajmalnik‐Brown () and included a buffer of 30 mM bicarbonate (HCO 3 − ).…”

“…The Zara‐10 enrichment culture (Delgado et al, ), which contains Dehalococcoides sp. and exhibits a high rate of trichloroethene (TCE) dechlorination (2.76 ± 0.34 mmol Cl − released per L per day), is a promising anaerobic culture for reductively dechlorinating TCE to ethene.…”

Ecophysiology and environmental distribution of organohalide-respiring bacteria

“…Triclosan addition to agricultural soil from Fairfax, Minnesota, USA, without previous exposure to this substrate increased abundance of Dehalococcoides-like Chloroflexi in soil microcosms [230]. Furthermore, recently the enrichment of a TCE respiring consortium from garden soil collected from Cuzdrioara, Cluj County, Romania, was reported [231]. In spite of the presence of D.…”

“…The authors hypothesized that this might be a consequence of the intrinsic competition for electron donor (H2) in soils and sediments, driven by a variety of electron acceptors such as nitrate, Fe (III), sulfate, and bicarbonate [231].…”