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Dehalococcoides is a genus of bacteria within the class Dehalococcoidetes that conserve metabolic energy by coupling the oxidation of hydrogen gas (H2) with the reduction of halogenated organic compounds through a process known as reductive dehalogenation. It should be noted that a formal description of the candidate genus Dehalococcoides has not been published in the taxonomic literature to date, and that Dehalococcoides is currently absent from the List of Bacterial names with Standing in Nomenclature. The first Dehalococcoides  enrichment was performed in the year 1995 (REF), and the first isolate, Dehalococcoides ethenogenes strain 195, was described in 1997 (REF). Strain 195 gained notoriety as the first known organism capable of complete reduction of the dry-cleaning solvent, tetrachloroethene, also referred to as PCE. This finding is especially important to the field of bioremediation and environmental protection because PCE and other chloroethenes comprise the most common groundwater contaminants in the United States of America ((REF)). They are similarly ubiquitous throughout the developed world ((REF)). The complete reduction of PCE to ethene by Dehalococcoides occurs in a step-wise manner.



Although there are other dechlorinating microbesresponsible for the environmental catalysis of PCE → TCE → 1,2-Dichloroethene (1,2-DCE), only Dehalococcoides are known to continue the degradation sequence from 1,2-DCE to vinyl chloride (VC), and finally, ethene (1,2-DCE → VC → ethene), which is environmentally benign. The presence of Dehalococcoides in groundwater may be necessary for proper bioremediation of contaminated sites. In addition to chloroethenes, members of Dehalococcoides are now known to be capable of the reductive dehalogenation of other priority pollutants, including polychlorinated biphenyls, dioxins, chlorobenzenes, chlorophenols, chloroethanes, etc. ((REFs))

Taxonomy / Phylogeny
Other strains of Dehalococcoides have since been identified and isolated, each having varying capabilities for the dechlorination of halogenated organic comounds. The following is a list of Dehalococcoides strains and enrichment cultures described in the primary scientific literature, in order of first description.

Reductive Dehalogenation
What is known about the process of reductive dehalogenation in Dehalococcoides to date.

Bioremediation
High Dehalococcoides population numbers and electron substrate concentrations are necessary for effective bioremediation of dense non-aqueous phase liquids (DNAPL) at contaminated sites. Addition of either fermentable organic compounds (e.g. lactate or propionate) to create H2 in situ, is typically required. Often contaminated sites lack a native population of Dehalococcoides that can effectively remediate the contaminants, in which case bioaugmentation of the site with a mixed culture containing specific Dehalococcoides strains is required.

Nutritional Requirements
A comparison of media uses and a list of known or suspected nutritional requirements.