Halorespiration

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Organohalide respiration (OHR) (previously named halorespiration or dehalorespiration) is the use of halogenated compounds as terminal electron acceptors in anaerobic respiration. [1] [2] [3] Organohalide respiration can play a part in microbial biodegradation. The most common substrates are chlorinated aliphatics (PCE, TCE, chloroform) and chlorinated phenols. Organohalide-respiring bacteria are highly diverse. This trait is found in some Campylobacterota, Thermodesulfobacteriota, Chloroflexota (green nonsulfur bacteria), low G+C gram positive Clostridia, [4] and ultramicrobacteria. [5]

Contents

Process of organohalide respiration

The process of organohalide respiration, uses reductive dehalogenation to produce energy that can be used by the respiring microorganism to carry out its growth and metabolism. [6] Halogenated organic compounds are used as the terminal electron acceptor, which results in their dehalogenation. [6] Reductive dehalogenation is the process by which this occurs. [6] It involves the reduction of halogenated compounds by removing the halogen substituents, while simultaneously adding electrons to the compound. [7] Hydrogenolysis and vicinal reduction are the two known processes of this mechanism that have been identified. [7] In both processes, the removed halogen substituents are released as anions. [7] Reductive dehalogenation is catalyzed by reductive dehalogenases, which are membrane-associated enzymes. [6] [8] [3] A number of not only membrane-associated but also cytoplasmic hydrogenases, in some cases as part of the protein complexes, are predicted to play roles in the organohalide respiration process. [9] Most of these enzymes contain iron-sulfur (Fe-S) clusters, and a corrinoid cofactor at their active sites. [6] Although the exact mechanism is unknown, research suggests that these two components of the enzyme may be involved in the reduction. [6]

Substrates Used and Environmental Significance

Common substrates that are used as terminal electron acceptors in organohalide respiration are organochloride pesticides, aryl halides and alkyl solvents. [7] Many of these are persistent and toxic pollutants that can only be degraded anaerobically by organohalide respiration, either partially or completely. [6] [7] Trichloroethylene (TCE) and tetrachloroethylene (PCE) are two examples of such pollutants, and their degradation has been a focus of research. [6] [7] [10] PCE is an alkyl solvent that was previously used in dry cleaning, degreasing machinery and other applications. [6] [7] It remains a common contaminant of groundwater. [6] [7] Bacteria that are capable of completely degrading PCE to ethene, a nontoxic chemical, have been isolated. [10] They have been found to belong to the genus Dehalococcoides and to use H2 as their electron donor. [10] The process of organohalide respiration has been applied to in situ bioremediation of PCE and TCE in the past. [6] [8] For example, enhanced reductive dechlorination has been used to treat contaminated groundwater by introducing electron donors and dehalorespiring bacteria into the contaminated site, to create conditions that stimulate bacterial growth and organohalide respiration. [8] In enhanced reductive dechlorination, the pollutants act as the electron acceptors and are completely reduced to ultimately produce ethene in a series of reactions. [8]

Uses in Bioremediation

An ecologically significant aspect of bacterial organohalide respiration is the reduction of tetrachloroethene (PCE) and Trichloroethene (TCE); anthropogenic pollutants with high neuro and hepatotoxicity. [11] Their presence as environmental pollutants arose from their common industrial use as metal-degreasing agents from the 1920s - 1970. [12] These xenobiotic compounds tend to form partially insoluble layers called dense non-aqueous phase liquids (DNAPLs) at the bottom of groundwater aquifers, which solubilize in a slow, reservoir-like manner, making TCE and PCE among the most common groundwater pollutants. [13]

A commonly used strategy for the removal of TCE and PCE from groundwater is the use of bioremediation via enhanced reductive dechlorination (ERD). [14] ERD involves in-situ injections of dehalorespiring bacteria, among fermentable organic substrates serving as electron donors, while the two pollutants, TCE and PCE, act as the electron acceptors. [14] This facilitates the sequential dechlorination of PCE and TCE into noxious cis- dichloroethene (DCE) and Vinyl chloride (VC), which then suit as electron acceptors for the full dechlorination into innocuous ethene. [14]

A wide array of bacteria across different genera have the capacity to partially dechlorinate PCE and TCE into cis-DCE and VC. [14] One such example of this is the Magnetospirillum bacterium, strain MS-1, which can reduce PCE into cis-DCE under aerobic conditions. [15] However, these daughter substrates have higher toxicity profiles than their parent compounds. [14] As such, effective dechlorination of cis-DCE and VC into innocuous ethene is crucial for bioremediation of PCE and TCE-contaminated aquifers. [14] Currently, bacteria of the Dehalococcoides genera are the only known organisms that can fully dechlorinate PCE into ethene. This is due to their specific transmembrane reductive dehalogenases (RDases) that metabolize the chlorine atoms on the xenobiotic pollutants for cellular energy. [16] In particular, Dehalococcoides isolates VS and BAV1 encode Vinyl Chloride RDases, which metabolize VC into innocuous ethene, making them required species in ERD systems used in bioremediation of PCE and TCE. [16]

See also

Related Research Articles

<span class="mw-page-title-main">Bioremediation</span> Process used to treat contaminated media such as water and soil

Bioremediation broadly refers to any process wherein a biological system, living or dead, is employed for removing environmental pollutants from air, water, soil, flue gasses, industrial effluents etc., in natural or artificial settings. The natural ability of organisms to adsorb, accumulate, and degrade common and emerging pollutants has attracted the use of biological resources in treatment of contaminated environment. In comparison to conventional physicochemical treatment methods bioremediation may offer advantages as it aims to be sustainable, eco-friendly, cheap, and scalable.

Anaerobic respiration is respiration using electron acceptors other than molecular oxygen (O2). Although oxygen is not the final electron acceptor, the process still uses a respiratory electron transport chain.

In organochlorine chemistry, reductive dechlorination describes any chemical reaction which cleaves the covalent bond between carbon and chlorine via reductants, to release chloride ions. Many modalities have been implemented, depending on the application. Reductive dechlorination is often applied to remediation of chlorinated pesticides or dry cleaning solvents. It is also used occasionally in the synthesis of organic compounds, e.g. as pharmaceuticals.

Biological augmentation is the addition of archaea or bacterial cultures required to speed up the rate of degradation of a contaminant. Organisms that originate from contaminated areas may already be able to break down waste, but perhaps inefficiently and slowly.

Cometabolism is defined as the simultaneous degradation of two compounds, in which the degradation of the second compound depends on the presence of the first compound. This is in contrast to simultaneous catabolism, where each substrate is catabolized concomitantly by different enzymes. Cometabolism occurs when an enzyme produced by an organism to catalyze the degradation of its growth-substrate to derive energy and carbon from it is also capable of degrading additional compounds. The fortuitous degradation of these additional compounds does not support the growth of the bacteria, and some of these compounds can even be toxic in certain concentrations to the bacteria.

Dehalococcoides is a genus of bacteria within class Dehalococcoidia that obtain energy via the oxidation of hydrogen and subsequent reductive dehalogenation of halogenated organic compounds in a mode of anaerobic respiration called organohalide respiration. They are well known for their great potential to remediate halogenated ethenes and aromatics. They are the only bacteria known to transform highly chlorinated dioxins, PCBs. In addition, they are the only known bacteria to transform tetrachloroethene to ethene.

Microbial biodegradation is the use of bioremediation and biotransformation methods to harness the naturally occurring ability of microbial xenobiotic metabolism to degrade, transform or accumulate environmental pollutants, including hydrocarbons, polychlorinated biphenyls (PCBs), polyaromatic hydrocarbons (PAHs), heterocyclic compounds, pharmaceutical substances, radionuclides and metals.

In enzymology, a tetrachloroethene reductive dehalogenase is an enzyme that catalyzes the chemical reaction. This is a member of reductive dehalogenase enzyme family.

A dehalogenase is a type of enzyme that catalyzes the removal of a halogen atom from a substrate.

Dehalococcoidia is a class of Chloroflexota, a phylum of Bacteria. It is also known as the DHC group.

Dehalobacter restrictus is a species of bacteria in the phylum Bacillota. It is strictly anaerobic and reductively dechlorinates tetra- and trichloroethene. It does not form spores; it is a small, gram-positive rod with one lateral flagellum. PER-K23 is its type strain.

Desulfitobacterium dehalogenans is a species of bacteria. They are facultative organohalide respiring bacteria capable of reductively dechlorinating chlorophenolic compounds and tetrachloroethene. They are anaerobic, motile, Gram-positive and rod-shaped bacteria capable of utilizing a wide range of electron donors and acceptors. The type strain JW/IU-DCT, DSM 9161, NCBi taxonomy ID 756499.

Desulfitobacterium hafniense is a species of gram positive bacteria, its type strain is DCB-2T..

Desulfuromonas michiganensis is a species of tetrachloroethene-reducing, acetate-oxidizing anaerobic bacteria.

Geobacter lovleyi is a gram-negative metal-reducing and tetrachloroethene-dechlorinating proteobacterium. It has potential as a bioremediation organism, and is actively researched as such.

Dehalogenimonas lykanthroporepellens is an anaerobic, Gram-negative bacteria in the phylum Chloroflexota isolated from a Superfund site in Baton Rouge, Louisiana. It is useful in bioremediation for its ability to reductively dehalogenate chlorinated alkanes.

Adsorbable organic halides (AOX) is a measure of the organic halogen load at a sampling site such as soil from a land fill, water, or sewage waste. The procedure measures chlorine, bromine, and iodine as equivalent halogens, but does not measure fluorine levels in the sample.

Desulfuromonas is a Gram negative bacterial genus from the family of Desulfuromonadaceae. Desulfuromonas can reduce elemental sulfur to H2S. Desulfuromonas occur in anoxic sediments and saline lakes.

Polychorinated biphenyls, or PCBs, are a type of chemical that was widely used in the 1960s and 1970s, and which are a contamination source of soil and water. They are fairly stable and therefore persistent in the environment. Bioremediation of PCBs is the use of microorganisms to degrade PCBs from contaminated sites, relying on multiple microorganisms' co-metabolism. Anaerobic microorganisms dechlorinate PCBs first, and other microorganisms that are capable of doing BH pathway can break down the dechlorinated PCBs to usable intermediates like acyl-CoA or carbon dioxide. If no BH pathway-capable microorganisms are present, dechlorinated PCBs can be mineralized with help of fungi and plants. However, there are multiple limiting factors for this co-metabolism.

Reductive dehaholagenses (EC 1.97.1.8) are a group of enzymes utilized in organohalide respiring bacteria. These enzymes are mostly attached to the periplasmic side of the cytoplasmic membrane and play a central role in energy-conserving respiratory process for organohalide respiring bacteria by reducing organohalides. During such reductive dehalogenation reaction, organohalides are used as terminal electron acceptors. They catalyze the following general reactions:

References

  1. ↑ Holliger, C.; Wohlfarth, G.; Diekert, G. (1998). "Reductive dechlorination in the energy metabolism of anaerobic bacteria" (PDF). FEMS Microbiology Reviews. 22 (5): 383. doi:10.1111/j.1574-6976.1998.tb00377.x.
  2. ↑ Jugder, Bat-Erdene; Ertan, Haluk; Bohl, Susanne; Lee, Matthew; Marquis, Christopher P.; Manefield, Michael (2016). "Organohalide Respiring Bacteria and Reductive Dehalogenases: Key Tools in Organohalide Bioremediation". Frontiers in Microbiology. 7: 249. doi: 10.3389/fmicb.2016.00249 . ISSN   1664-302X. PMC   4771760 . PMID   26973626.
  3. 1 2 Jugder, Bat-Erdene; Ertan, Haluk; Lee, Matthew; Manefield, Michael; Marquis, Christopher P. (2015-10-01). "Reductive Dehalogenases Come of Age in Biological Destruction of Organohalides". Trends in Biotechnology. 33 (10): 595–610. doi:10.1016/j.tibtech.2015.07.004. ISSN   0167-7799. PMID   26409778.
  4. ↑ Hiraishi, A. (2008). "Biodiversity of Dehalorespiring Bacteria with Special Emphasis on Polychlorinated Biphenyl/Dioxin Dechlorinators". Microbes and Environments. 23 (1): 1–12. doi: 10.1264/jsme2.23.1 . PMID   21558680.
  5. ↑ Duda, V. I.; Suzina, N. E.; Polivtseva, V. N.; Boronin, A. M. (2012). "Ultramicrobacteria: Formation of the concept and contribution of ultramicrobacteria to biology". Microbiology. 81 (4): 379–390. doi:10.1134/S0026261712040054. PMID   23156684. S2CID   6391715.
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  7. 1 2 3 4 5 6 7 8 Mohn, W. W.; Tiedje, J. M. (September 1992). "Microbial reductive dehalogenation". Microbiological Reviews. 56 (3): 482–507. doi:10.1128/mmbr.56.3.482-507.1992. ISSN   0146-0749. PMC   372880 . PMID   1406492.
  8. 1 2 3 4 Scheutz, Charlotte; Durant, Neal d.; Dennis, Philip; Hansen, Maria Heisterberg; Jørgensen, Torben; Jakobsen, Rasmus; Cox, Evan e.; Bjerg, Poul L. (2008). "Concurrent Ethene Generation and Growth of Dehalococcoides Containing Vinyl Chloride Reductive Dehalogenase Genes During an Enhanced Reductive Dechlorination Field Demonstration". Environmental Science & Technology. 42 (24): 9302–9309. Bibcode:2008EnST...42.9302S. doi:10.1021/es800764t. PMID   19174908.
  9. ↑ Jugder, Bat-Erdene; Ertan, Haluk; Wong, Yie Kuan; Braidy, Nady; Manefield, Michael; Marquis, Christopher P.; Lee, Matthew (2016-08-10). "Genomic, transcriptomic and proteomic analyses of Dehalobacter UNSWDHB in response to chloroform". Environmental Microbiology Reports. 8 (5): 814–824. Bibcode:2016EnvMR...8..814J. doi:10.1111/1758-2229.12444. ISSN   1758-2229. PMID   27452500.
  10. 1 2 3 Maymó-Gatell, X.; Chien, Y.; Gossett, J. M.; Zinder, S. H. (1997-06-06). "Isolation of a bacterium that reductively dechlorinates tetrachloroethene to ethene". Science. 276 (5318): 1568–1571. doi:10.1126/science.276.5318.1568. ISSN   0036-8075. PMID   9171062.
  11. ↑ Ruder, AM (September 2006). "Potential health effects of occupational chlorinated solvent exposure". Annals of the New York Academy of Sciences. 1076 (1): 207–227. Bibcode:2006NYASA1076..207R. doi:10.1196/annals.1371.050. PMID   17119204. S2CID   43678533.
  12. ↑ Bakke, Berit; Stewart, Patricia A.; Waters, Martha A. (November 2007). "Uses of an Exposure to Trichloroethylene in U.S Industry: A Systematic Literature Review". Journal of Occupational and Environmental Hygiene. 4 (5): 375–390. doi:10.1080/15459620701301763. PMID   17454505. S2CID   32801149.
  13. ↑ Dugat-Bony, Eric (March 2012). "In situ TCE degradation mediated by complex dehalorespiring communities during biostimulation processes". Microbial Biotechnology. 5 (5): 642–653. doi:10.1111/j.1751-7915.2012.00339.x. PMC   3815876 . PMID   22432919.
  14. 1 2 3 4 5 6 Scheutz, Charlotte (November 2008). "Concurrent ethene generation and growth of Dehalococcoides containing vinyl chloride reductive dehalogenase genes during an enhanced reductive dechlorination field demonstration". Environmental Science & Technology. 42 (24): 9302–9309. Bibcode:2008EnST...42.9302S. doi:10.1021/es800764t. PMID   19174908.
  15. ↑ Sharma, Pramod K (March 1996). "Isolation and Characterization of a Facultatively Aerobic Bacterium That Reductively Dehalogenates Tetrachloroethene to cis-1,2-Dichloroethene". Applied and Environmental Microbiology. 62 (3): 761–765. Bibcode:1996ApEnM..62..761S. doi:10.1128/aem.62.3.761-765.1996. PMC   1388792 . PMID   16535267.
  16. 1 2 Khoshnood, Behrang (August 2015). "Genome Closing and Transcription Kinetics for RDase Genes in Dehalococcoides and Their Prevalence in a Wastewater Treatment Plant". National University of Singapore Libraries. Archived from the original on 2017-12-01. Retrieved 2017-11-19– via Proquest.

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