Anaerobic biodegradation of chloroform and dichloromethane with a Dehalobacter enrichment culture

Chloroform (CF) and dichloromethane (DCM) are among the more commonly identified chlorinated aliphatic compounds found in contaminated soil and groundwater. Complete dechlorination of CF has been reported under anaerobic conditions by microbes that respire CF to DCM and others that biodegrade DCM. The objectives of this study were to ascertain if a commercially available bioaugmentation enrichment culture (KB-1® Plus) uses an oxidative or fermentative pathway for biodegradation of DCM; and to determine if the products from DCM biodegradation can support organohalide respiration of CF to DCM in the absence of an exogenous electron donor. In various treatments with the KB-1® Plus culture to which 14C-CF was added, the predominant product was 14CO2, indicating that oxidation is the predominant pathway for DCM. Recovery of 14C-DCM when biodegradation was still in progress confirmed that CF first undergoes reductive dechlorination to DCM. 14C-labeled organic acids, including acetate and propionate, were also recovered, suggesting that synthesis of organic acids provides a sink for the electron equivalents from oxidation of DCM. When the culture was washed to remove organic acids from prior additions of exogenous electron donor and only CF and DCM were added, the culture completely dechlorinated CF. The total amount of DCM added was not sufficient to provide the electron equivalents needed to reduce CF to DCM. Thus, the additional reducing power came via the DCM generated from CF reduction. Nevertheless, the rate of CF consumption was considerably slower in comparison to treatments that received an exogenous electron donor.

Identification of a fully dechlorinated product of chlordecone in soil microcosms and enrichment cultures

ABSTRACTAnaerobic microcosms constructed with soil from Guadeloupe, amended with electron donor (ethanol and acetone) and incubated for more than a decade, transformed chlordecone (CLD) into a suite of progressively more dechlorinated products, including a fully dechlorinated carboxylated indene product. This fully dechlorinated transformation product has never before been observed and indicates that complete dechlorination of CLD is possible. The carboxylated indene was detected by LC-MS and structure was confirmed by LC-MS/MS using a Q-Exactive Orbitrap mass spectrometer.

Reduction of 1,2,3-trichloropropane (TCP): pathways and mechanisms from computational chemistry calculations

Lesser halogenated halocarbons such as 1,2,3-trichloropropane (TCP) are persistent under most conditions, but reductive beta-elimination favors complete dechlorination by hydrogenolysis of the allyl chloride intermediate.

Identification of Multiple Dehalogenase Genes Involved in Tetrachloroethene-to-Ethene Dechlorination in aDehalococcoides-Dominated Enrichment Culture

Chloroethenes (CEs) are widespread groundwater toxicants that are reductively dechlorinated to nontoxic ethene (ETH) by members ofDehalococcoides. This study established aDehalococcoides-dominated enrichment culture (designated “YN3”) that dechlorinates tetrachloroethene (PCE) to ETH with high dechlorination activity, that is, complete dechlorination of 800 μM PCE to ETH within 14 days in the presence ofDehalococcoidesspecies at5.7±1.9×107 copies of 16S rRNA gene/mL. The metagenome of YN3 harbored 18rdhAgenes (designatedYN3rdhA1–18) encoding the catalytic subunit of reductive dehalogenase (RdhA), four of which were suggested to be involved in PCE-to-ETH dechlorination based on significant increases in their transcription in response to CE addition. The predicted proteins for two of these four genes, YN3RdhA8 and YN3RdhA16,showed 94% and 97% of amino acid similarity with PceA and VcrA, which are well known to dechlorinate PCE to trichloroethene (TCE) and TCE to ETH, respectively. The other twordhAs,YN3rdhA6andYN3rdhA12,which were never proved asrdhAfor CEs, showed particularly high transcription upon addition of vinyl chloride (VC), with75±38and16±8.6mRNA copies per gene, respectively, suggesting their possible functions as novel VC-reductive dehalogenases. Moreover, metagenome data indicated the presence of three coexisting bacterial species, including novel species of the genusBacteroides, which might promote CE dechlorination byDehalococcoides.