User:A hashimi/sandbox

Activities
Dehalococcoides are obligately organohalide-respiring bacteria, which means that they can only grow by using halogenated compounds as electron acceptor. They use hydrogen as an electron donor. Energy is generated by transferring electrons from hydrogen to the halogenated electron acceptor. To synthesize cell material Dehalococcoides strains additionally need actate.

Dehalococcoides can transform many highly toxic and/or persistent compounds that are not transformed by any other known bacteria. This included tetrachloroethene (PCE) and trichloroethene (TCE) which is transformed to the non-toxic ethene, chlorinated dioxins, benzenes, PCBs, phenols and many other aromatic substrates.

Application
By transforming all these halogenated compounds they are seen as an important helper to treat contaminated ground water sites. Their capacity to grow by using the contaminants as energy source allows them to distribute in a contaminated soil or groundwater and offers great promises for the in situ use. Several companies worldwide now use Dehalococcoides-containing mixed cultures for commercial remediation efforts.

The presence of bacteria of the genus Dehalococcoides is a prerequisite to induce complete detoxification of halogenated ethenes (often described as dense non-aqueous phase liquids (DNAPL)) to the non-toxic ethene. For treatment of contaminated sites apart from an active culture also electron acceptors have to be added. Most often, these are oxidizable substrates (e.g. lactate) to form hydrogen in situ.

Activities
Dehalococcoides are obligately organohalide-respiring bacteria, meaning that they can only grow by using halogenated compounds as electron acceptors. They use hydrogen as an electron donor and acetate as a carbon source. Energy is generated by transferring electrons from hydrogen to the halogenated electron acceptor, thus dehalogenating the compound in the process.

Dehalococcoides can transform many highly toxic and/or persistent compounds. This includes tetrachloroethene (PCE) and trichloroethene (TCE) which are transformed to non-toxic ethene, and chlorinated dioxins, vinyl chloride, benzenes, polychlorinated biphenyls (PCBs), phenols and many other aromatic contaminants.

Application
Dehalococcoides are seen as important helpers in treating contaminated sites because of their ability to transform halogenated compounds. Their capacity to grow by using contaminants allows them to proliferate in contaminated soil or groundwater, offering promise for in situ decontamination efforts.

The process of transforming halogenated pollutants to non-toxic compounds involves different reductive enzymes. D. mccartyi strain BAV1 is able to reduce vinyl chloride, a toxic contaminant that usually originates from landfills, to ethene by using a special vinyl chloride reductase thought to be coded for by the bvcA gene. A chlorobenzene reductive dehalogenase has also been identified in the strain CBDB1.

Several companies worldwide now use Dehalococcoides-containing mixed cultures in commercial remediation efforts. In mixed cultures, other bacteria present can augment the dehalogenation process by producing metabolic products that can be used by Dehalococcoides and others involved in the degradation process. [4][7] For example, Dehalococcoides sp. strain WL can work alongside Dehalobacter in a step-wise manner to degrade vinyl chloride: Dehalobacter converts 1,1,2-TCA to vinyl chloride, which is subsequently degraded by Dehalococcoides. Also, the addition of electron acceptors is needed - they are converted to hydrogen in situ by other bacteria present, which can then be used as an electron source by Dehalococcoides. MEAL (a methanol, ethanol, acetate, and lactate mixture) is documented to have been used as substrate. In the US, BAV1 was patented for the in situ reductive dechlorination of vinyl chlorides and dichloroethenes in 2007. D. mccartyi in high-density dechlorinating bioflocs have also been used in ex situ bioremediation.

However, not all members of Dehalococcoides can reduce all halogenated contaminants. Certain strains cannot use PCE or TCE as electron acceptors (e.g. CBDB1) and some cannot use vinyl chloride as an electron acceptor (e.g. FL2). D. mccartyi strains 195 and SFB93 are inhibited by high concentrations of acetylene (which builds up in contaminated groundwater sites as a result of TCE degradation) via changes in gene expression that likely disrupt normal electron transport chain function. When selecting Dehalococcoides strains for bioremediation use, it is important to consider their metabolic capabilities and their sensitivities to different chemicals.