Editing Reductive dechlorination (section)

===Bioremediation using reductive dechlorination===

Reductive dechlorination of chlorinated organic molecules is relevant to [[bioremediation]] of polluted groundwater.<ref>{{Cite journal|date=2015-10-01|title=Reductive Dehalogenases Come of Age in Biological Destruction of Organohalides|journal=Trends in Biotechnology|language=en|volume=33|issue=10|pages=595–610|doi=10.1016/j.tibtech.2015.07.004|pmid=26409778|issn=0167-7799|last1=Jugder|first1=Bat-Erdene|last2=Ertan|first2=Haluk|last3=Lee|first3=Matthew|last4=Manefield|first4=Michael|last5=Marquis|first5=Christopher P.}}</ref><ref>{{Cite journal|last1=Jugder|first1=Bat-Erdene|last2=Ertan|first2=Haluk|last3=Bohl|first3=Susanne|last4=Lee|first4=Matthew|last5=Marquis|first5=Christopher P.|last6=Manefield|first6=Michael|date=2016|title=Organohalide Respiring Bacteria and Reductive Dehalogenases: Key Tools in Organohalide Bioremediation|journal=Frontiers in Microbiology|language=en|volume=7|page=249|doi=10.3389/fmicb.2016.00249|pmid=26973626|pmc=4771760|issn=1664-302X|doi-access=free}}</ref> One example<ref>{{cite journal | display-authors = etal | year = 2000 | title = still a cause for concern | journal = Environ Health Perspect | volume = 108 | issue = 7| pages = 579–88 | pmid = 10905993 | pmc = 1638183  | last1 = Kielhorn | first1 = J | last2 = Melber | first2 = C | last3 = Wahnschaffe | first3 = U | last4 = Aitio | first4 = A | last5 = Mangelsdorf | first5 = I | doi = 10.1289/ehp.00108579}}</ref> is the organochloride respiration of the dry-cleaning solvent, [[tetrachloroethylene]], and the engine degreasing solvent [[trichloroethylene]] by [[anaerobic bacteria]], often members of the candidate genera ''Dehalococcoides''. Bioremediation of these [[chloroethene]]s can occur when other microorganisms at the contaminated site provide H<sub>2</sub> as a natural byproduct of various [[Fermentation (biochemistry)|fermentation]] reactions. The dechlorinating bacteria use this H<sub>2</sub> as their electron donor, ultimately replacing [[chlorine]] atoms in the chloroethenes with hydrogen atoms via hydrogenolytic reductive dechlorination. This process can proceed in the soil provided the availability of organic electron donors and the appropriate strains of ''Dehalococcoides''. Trichloroethylene is dechlorinated via [[dichloroethene]] and [[vinyl chloride]] to [[ethylene]].<ref>{{cite journal | year = 1997 | title = Breathing with chlorinated solvents | journal = Science | volume = 276 | issue = 5318| pages = 1521–2 | pmid = 9190688  | last1 = McCarty | first1 = PL | doi = 10.1126/science.276.5318.1521| s2cid = 29183906 }}</ref>

A [[chloroform]]-degrading reductive dehalogenase enzyme has been reported in a ''[[Dehalobacter]]'' member. The chloroform reductive dehalogenase, termed TmrA, was found to be transcriptional up-regulated in response to chloroform respiration<ref>{{Cite journal|last1=Jugder|first1=Bat-Erdene|last2=Ertan|first2=Haluk|last3=Wong|first3=Yie Kuan|last4=Braidy|first4=Nady|last5=Manefield|first5=Michael|last6=Marquis|first6=Christopher P.|last7=Lee|first7=Matthew|date=2016-08-10|title=Genomic, transcriptomic and proteomic analyses ofDehalobacterUNSWDHB in response to chloroform|journal=Environmental Microbiology Reports|language=en|volume=8|issue=5|pages=814–824|doi=10.1111/1758-2229.12444|pmid=27452500|bibcode=2016EnvMR...8..814J |issn=1758-2229}}</ref> and the enzyme can be obtained both in native<ref>{{Cite journal|last1=Jugder|first1=Bat-Erdene|last2=Bohl|first2=Susanne|last3=Lebhar|first3=Helene|last4=Healey|first4=Robert D.|last5=Manefield|first5=Mike|last6=Marquis|first6=Christopher P.|last7=Lee|first7=Matthew|date=2017-06-20|title=A bacterial chloroform reductive dehalogenase: purification and biochemical characterization|journal=Microbial Biotechnology|language=en|volume=10|issue=6|pages=1640–1648|doi=10.1111/1751-7915.12745|issn=1751-7915|pmc=5658581|pmid=28631300}}</ref> and [[Recombinant protein production|recombinant]] forms.<ref>{{Cite journal|last1=Jugder|first1=Bat-Erdene|last2=Payne|first2=Karl A. P.|last3=Fisher|first3=Karl|last4=Bohl|first4=Susanne|last5=Lebhar|first5=Helene|last6=Manefield|first6=Mike|last7=Lee|first7=Matthew|last8=Leys|first8=David|last9=Marquis|first9=Christopher P.|date=2018-01-24|title=Heterologous Production and Purification of a Functional Chloroform Reductive Dehalogenase|journal=ACS Chemical Biology|language=en|volume=13|issue=3|pages=548–552|doi=10.1021/acschembio.7b00846|pmid=29363941|issn=1554-8929}}</ref>

Reductive dechlorination has been investigated for bioremediation of [[Polychlorinated biphenyl|polychlorinated biphenyls]] (PCB) and  [[Chlorofluorocarbon|chlorofluorocarbons]] (CFC). The reductive dechlorination of PCBs is performed by anaerobic microorganisms that utilize the PCB as an electron sink. The result of this is the reduction of the "meta" site, followed by the "para" site, and finally the "ortho" site, leading to a dechlorinated product.<ref name=":7">{{Cite journal|last1=Payne|first1=Rayford B.|last2=May|first2=Harold D.|last3=Sowers|first3=Kevin R.|date=2011-10-15|title=Enhanced Reductive Dechlorination of Polychlorinated Biphenyl Impacted Sediment by Bioaugmentation with a Dehalorespiring Bacterium|journal=Environmental Science & Technology|volume=45|issue=20|pages=8772–8779|doi=10.1021/es201553c|pmid=21902247|issn=0013-936X|pmc=3210572|bibcode=2011EnST...45.8772P}}</ref><ref name=":6">{{cite journal|last1=Tiedje|first1=James M.|last2=Quensen|first2=John F.|last3=Chee-Sanford|first3=Joann|last4=Schimel|first4=Joshua P.|last5=Boyd|first5=Stephen A.|title=Microbial reductive dechlorination of PCBs|journal=Biodegradation|date=1994|volume=4|issue=4|pages=231–240|doi=10.1007/BF00695971|pmid=7764920|s2cid=2596703}}</ref><ref name=":5">{{cite journal|last1=Quensen|first1=J. F.|last2=Tiedje|first2=J. M.|last3=Boyd|first3=S. A.|title=Reductive Dechlorination of Polychlorinated Biphenyls by Anaerobic Microorganisms from Sediments|journal=Science|date=4 November 1988|volume=242|issue=4879|pages=752–754|doi=10.1126/science.242.4879.752|pmid=17751997|bibcode=1988Sci...242..752Q|s2cid=35371230}}</ref> In the Hudson River, microorganisms effect dechlorination over the course of weeks. The resulting monochlorobiphenyls and dichlorobiphenyls are less toxic and more easily degradable by [[aerobic organism]]s compared to their chlorinated counterparts.<ref name=":5" /> The prominent drawback that has prevented the widespread use of reductive dechlorination for PCB detoxification and has decreased its feasibility is the issue of the slower than desired dechlorination rates.<ref name=":6" /> It has been suggested that [[bioaugmentation]] with DF-1 can lead to enhanced reductive dechlorination rates of PCBs through stimulation of dechlorination. Additionally, high inorganic carbon levels do not affect dechlorination rates in low PCB concentration environments.<ref name=":7" />

The reductive dechlorination applies to CFCs.<ref>{{Cite journal|last1=Lovley|first1=Derek R.|last2=Woodward|first2=Joan C.|date=1992-05-01|title=Consumption of Freons CFC-11 and CFC-12 by anaerobic sediments and soils|journal=Environmental Science & Technology|volume=26|issue=5|pages=925–929|doi=10.1021/es00029a009|issn=0013-936X|bibcode=1992EnST...26..925L}}</ref> Reductive dechlorination of CFCs including CFC-11, CFC-113, chlorotrifluoroethene, CFC-12, HCFC-141b, and tetrachloroethene occur through [[hydrogenolysis]]. Reduction rates of CFC mirror theoretical rates calculated based on the [[Marcus theory]] of electron transfer rate.<ref>{{Cite journal|last1=Balsiger|first1=Christian|last2=Holliger|first2=Christof|last3=Höhener|first3=Patrick|title=Reductive dechlorination of chlorofluorocarbons and hydrochlorofluorocarbons in sewage sludge and aquifer sediment microcosms|journal=Chemosphere|volume=61|issue=3|pages=361–373|doi=10.1016/j.chemosphere.2005.02.087|pmid=16182853|bibcode=2005Chmsp..61..361B|year=2005}}</ref>