Biodegradation - Cometabolic - Revision history

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‎Cometabolic Degradation of Emerging Contaminants and Other Trace Organics

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 *[[Bioremediation - Anaerobic]]
 *[[Biodegradation - Hydrocarbons]]
 '''Contributor(s):''' [[Dr. Kung-Hui (Bella) Chu]]
 '''Key Resource(s):'''

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 The cometabolic degradation phenomenon was first reported in 1958, observing that methane-utilizing bacterium Pseudomonas methanica (renamed as [[wikipedia:Methylomonas methanica | ''Methylomonas methanica'']]) could oxidize ethane and propane, but was unable to use these compounds as a carbon and energy source<ref name= "Hazen2010" />. [[wikipedia::Methane | Methane]] is a growth substrate for the methane-oxidizing bacterium, while ethane and propane are co-metabolic substrates. Subsequent studies have found that [[wikipedia:Methanotroph | methanotrophs]] can cometabolically transform [[Polycyclic Aromatic Hydrocarbons (PAHs) | polycyclic aromatic hydrocarbons (PAHs)]], explosives, dioxane, polychlorinated biphenyls (PCBs), pesticides, and [[wikipedia: Methyl tert-butyl ether | methyl tertiary-butyl ether]] (MTBE)<ref name= "Dalton1982" />. In addition to methane-oxidizing bacteria, many other microorganisms, particularly oxygenase-expressing cultures, could cometabolically degrade persistent man-made compounds like chlorinated pesticides, halogenated aliphatic, and aromatic compounds<ref name= "Janke1985">Janke, D. and Fritsche, W., 1985. Nature and significance of microbial cometabolism of xenobiotics. Journal of Basic Microbiology, 25(9), 603-619. [https://doi.org/10.1002/jobm.3620250910 doi: 10.1002/jobm.3620250910]</ref><ref name= "Hanson1996">Hanson, R.S. and Hanson, T.E., 1996. Methanotrophic bacteria. Microbiology and Molecular Biology Reviews, 60(2), 439-471.
-[https://doi.org/10.1128/mr.60.2.439-471.1996 doi:10.1128/mr.60.2.439-471.1996] [[Media:Hanson1996.pdf | Article.pdf]]</ref>.
+[https://doi.org/10.1128/mr.60.2.439-471.1996 doi:10.1128/mr.60.2.439-471.1996] [[Media:Hanson1996.pdf | Article pdf]]</ref>.
 ==Mechanisms of Cometabolism==
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 ==Application of Cometabolic Biodegradation for Environmental Pollutants==
-Aerobic and anaerobic cometabolic bioremediation have been applied under different environmental conditions to remove contaminants including chlorinated solvents, MTBE, TNT, BTEX, and atrazine<ref name= "Hand2015">Hand, S., Wang, B. and Chu, K.H., 2015. Biodegradation of 1, 4-dioxane: Effects of enzyme inducers and trichloroethylene. Science of The Total Environment, 520, 154-159. [http://dx.doi.org/10.1016/j.scitotenv.2015.03.031 doi: 10.1016/j.scitotenv.2015.03.031]</ref>. Methanotrophic-based, large-scale bioremediation for chlorinated solvents (like TCE) has successfully demonstrated<ref name= "Hand2015" />. There are several common classes of environmental pollutants that can undergo cometabolic degradation by various bacteria under aerobic and anaerobic conditions (Table 1). New studies also reported cometabolic degradation of emerging contaminants including MTBE<ref>Kim, M.H., Wang, N. and Chu, K.H., 2014. 6: 2 Fluorotelomer alcohol (6: 2 FTOH) biodegradation by multiple microbial species under different physiological conditions. Applied Microbiology and Biotechnology, 98(4), 1831-1840. [https://doi.org/10.1007/s00253-013-5131-3 doi:10.1007/s00253-013-5131-3]</ref>, [[1,2,3-Trichloropropane | 1,2,3-trichlopropane (TCP)]], 1,4-dioxane<ref name= "Lewis2016BIO">Lewis, M., Kim, M.H., Liu, E.J., Wang, N. and Chu, K.H., 2016. Biotransformation of 6: 2 polyfluoroalkyl phosphates (6: 2 PAPs): Effects of degradative bacteria and co-substrates. Journal of Hazardous Materials, 320, 479-486. [http://dx.doi.org/10.1016/j.jhazmat.2016.08.036 doi: 10.1016/j.jhazmat.2016.08.036]</ref><ref name= "Lewis2016ENG">Lewis, M., Kim, M.H., Wang, N. and Chu, K.H., 2016. Engineering artificial cs in Microbiology, 24(4), 335-373. [http://dx.doi.org/10.1080/10408419891294217 doi: 10.1080/10408419891294217 ]</ref>, N-nitroso-dimethylamine (NDMA), and [[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS) | poly-fluoroalkyl substances]] like fluorotelomer alcohols<ref>Chu, K.H. and Alvarez-Cohen, L., 1999. Evaluation of toxic effects of aeration and trichloroethylene oxidation on methanotrophic bacteria grown with different nitrogen sources. Applied and Environmental Microbiology, 65(2), 766-772. [https://doi.org/10.1128/AEM.65.2.766-772.1999 doi: 10.1128/AEM.65.2.766-772.1999] [[Media:Chu1999.pdf | Article.pdf]]</ref><ref name= "Chu1998">Chu, K.H. and Alvarez-Cohen, L., 1998. Effect of nitrogen source on growth and trichloroethylene degradation by methane-oxidizing bacteria. Applied and Environmental Microbiology, 64(9), 3451-3457. [https://doi.org/10.1128/AEM.64.9.3451-3457.1998 doi: 10.1128/AEM.64.9.3451-3457.1998] [[Media:Chu1998.pdf | Article.pdf]]</ref><ref name= "AlvarezC2001" />, and some of this knowledge has been applied to remediation in the field in recent years.
+Aerobic and anaerobic cometabolic bioremediation have been applied under different environmental conditions to remove contaminants including chlorinated solvents, MTBE, TNT, BTEX, and atrazine<ref name= "Hand2015">Hand, S., Wang, B. and Chu, K.H., 2015. Biodegradation of 1, 4-dioxane: Effects of enzyme inducers and trichloroethylene. Science of The Total Environment, 520, 154-159. [http://dx.doi.org/10.1016/j.scitotenv.2015.03.031 doi: 10.1016/j.scitotenv.2015.03.031]</ref>. Methanotrophic-based, large-scale bioremediation for chlorinated solvents (like TCE) has successfully demonstrated<ref name= "Hand2015" />. There are several common classes of environmental pollutants that can undergo cometabolic degradation by various bacteria under aerobic and anaerobic conditions (Table 1). New studies also reported cometabolic degradation of emerging contaminants including MTBE<ref>Kim, M.H., Wang, N. and Chu, K.H., 2014. 6: 2 Fluorotelomer alcohol (6: 2 FTOH) biodegradation by multiple microbial species under different physiological conditions. Applied Microbiology and Biotechnology, 98(4), 1831-1840. [https://doi.org/10.1007/s00253-013-5131-3 doi:10.1007/s00253-013-5131-3]</ref>, [[1,2,3-Trichloropropane | 1,2,3-trichlopropane (TCP)]], 1,4-dioxane<ref name= "Lewis2016BIO">Lewis, M., Kim, M.H., Liu, E.J., Wang, N. and Chu, K.H., 2016. Biotransformation of 6: 2 polyfluoroalkyl phosphates (6: 2 PAPs): Effects of degradative bacteria and co-substrates. Journal of Hazardous Materials, 320, 479-486. [http://dx.doi.org/10.1016/j.jhazmat.2016.08.036 doi: 10.1016/j.jhazmat.2016.08.036]</ref><ref name= "Lewis2016ENG">Lewis, M., Kim, M.H., Wang, N. and Chu, K.H., 2016. Engineering artificial cs in Microbiology, 24(4), 335-373. [http://dx.doi.org/10.1080/10408419891294217 doi: 10.1080/10408419891294217 ]</ref>, N-nitroso-dimethylamine (NDMA), and [[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS) | poly-fluoroalkyl substances]] like fluorotelomer alcohols<ref>Chu, K.H. and Alvarez-Cohen, L., 1999. Evaluation of toxic effects of aeration and trichloroethylene oxidation on methanotrophic bacteria grown with different nitrogen sources. Applied and Environmental Microbiology, 65(2), 766-772. [https://doi.org/10.1128/AEM.65.2.766-772.1999 doi: 10.1128/AEM.65.2.766-772.1999] [[Media:Chu1999.pdf | Article pdf]]</ref><ref name= "Chu1998">Chu, K.H. and Alvarez-Cohen, L., 1998. Effect of nitrogen source on growth and trichloroethylene degradation by methane-oxidizing bacteria. Applied and Environmental Microbiology, 64(9), 3451-3457. [https://doi.org/10.1128/AEM.64.9.3451-3457.1998 doi: 10.1128/AEM.64.9.3451-3457.1998] [[Media:Chu1998.pdf | Article pdf]]</ref><ref name= "AlvarezC2001" />, and some of this knowledge has been applied to remediation in the field in recent years.
   [[File:Chu-Article1-Table1.jpg|650px|thumbnail|right|Table 1. Cometabolic degradation of example pollutants under various conditions (modified from Hazen (2010)<ref name= "Hazen2010" />).]]
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 According to US Environmental Protection Agency (EPA), an emerging contaminant is defined as “a chemical or material characterized by a perceived, potential, or real threat to human health or the environment or by a lack of published health standards”<ref name= "USEPAEC"> US EPA Fact sheets about Emerging Contaminants. EPA 505-F-14-002. (Accessed October 27, 2016). [https://www.epa.gov/fedfac/emerging-contaminants-and-federal-facility-contaminants-concern US EPA Emerging Contaminants]</ref>. A number of technical fact sheets of emerging contaminants, including TCP, 1,4-dioxane, NDMA, and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) are available from the [https://www.epa.gov/fedfac/emerging-contaminants-and-federal-facility-contaminants-concern US EPA’s website] to guide  detection, analysis, and treatment of these emerging contaminants. Other emerging contaminants, such as poly-and per-fluoroalkyl substances (PFAS), pharmaceuticals and personal care products (PPCPs), and endocrine-disrupting compounds (EDCs) have also been the focus of intense research by scientists and engineers in recent years. Many of these emerging contaminants are also recalcitrant, but are subjected to cometabolic degradation by many different microbial strains under diverse conditions. Below is a brief description of studies reporting cometabolic degradation of selective emerging contaminants:
 *[[1,2,3-Trichloropropane | '''1,2,3-Trichlopropane (TCP).''']] TCP is a chlorinated hydrocarbon with high chemical stability. It is commonly detected in groundwater and soil, due to improper disposal. TCP is also a by-product or an intermediate in the production of various chemicals.  EPA has classified TCP as a suspected carcinogen to humans. An early study has showed that methane-oxidizing bacteria can degrade TCP cometabolically<ref>Bosma, T. and Janssen, D.B., 1998. Conversion of chlorinated propanes by Methylosinus trichosporium OB3b expressing soluble methane monooxygenase. Applied Microbiology and Biotechnology, 50(1), 105-112. [https://doi.org/10.1007/s002530051263 doi: 10.1007/s002530051263]</ref>. A more recent study also reported that some propane-oxidizing bacteria can cometabilize TCP effectively<ref> Chu, K. H., 2012. Biodegradation of 1,2,3-Trichloropropane, Texas Hazardous Waste Research Center Report, Project Report Number 060TAM2993.</ref>.
-*[[1,4-Dioxane |'''1,4-Dioxane.''']] 1,4-Dioxane is a likely human carcinogen and has been detected in groundwater at many sites. It is used as a solvent stabilizer in the manufacture and processing of paper, cotton, textile products, auto coolants, cosmetics, and shampoo. 1,4-dioxane can be degraded via both growth-linked<ref>Kim, Y.M., Jeon, J.R., Murugesan, K., Kim, E.J. and Chang, Y.S., 2009. Biodegradation of 1, 4-dioxane and transformation of related cyclic compounds by a newly isolated Mycobacterium sp. PH-06. Biodegradation, 20(4), 511-519. [https://doi.org/10.1007/s10532-008-9240-0 doi: 10.1007/s10532-008-9240-0]</ref><ref name= "Parales1994">Parales, R.E., Adamus, J.E., White, N. and May, H.D., 1994. Degradation of 1, 4-dioxane by an actinomycete in pure culture. Applied and Environmental Microbiology, 60(12), 4527-4530. [https://doi.org/10.1128/aem.60.12.4527-4530.1994 doi:10.1128/aem.60.12.4527-4530.1994] [[media:1994-Parales-Degradation_of_1%2C4-Dioxane_by_an_Actinomycete_in_Pure_Culture.pdf| Article.pdf]]</ref></ref> and cometabolic reactions<ref name= "Lewis2016BIO" />. Many oxygenase-expressing bacteria are able to degrade 1,4-dioxane to different degree under different physiological conditions.
+*[[1,4-Dioxane |'''1,4-Dioxane.''']] 1,4-Dioxane is a likely human carcinogen and has been detected in groundwater at many sites. It is used as a solvent stabilizer in the manufacture and processing of paper, cotton, textile products, auto coolants, cosmetics, and shampoo. 1,4-dioxane can be degraded via both growth-linked<ref>Kim, Y.M., Jeon, J.R., Murugesan, K., Kim, E.J. and Chang, Y.S., 2009. Biodegradation of 1, 4-dioxane and transformation of related cyclic compounds by a newly isolated Mycobacterium sp. PH-06. Biodegradation, 20(4), 511-519. [https://doi.org/10.1007/s10532-008-9240-0 doi: 10.1007/s10532-008-9240-0]</ref><ref name= "Parales1994">Parales, R.E., Adamus, J.E., White, N. and May, H.D., 1994. Degradation of 1, 4-dioxane by an actinomycete in pure culture. Applied and Environmental Microbiology, 60(12), 4527-4530. [https://doi.org/10.1128/aem.60.12.4527-4530.1994 doi:10.1128/aem.60.12.4527-4530.1994] [[media:1994-Parales-Degradation_of_1%2C4-Dioxane_by_an_Actinomycete_in_Pure_Culture.pdf| Article pdf]]</ref></ref> and cometabolic reactions<ref name= "Lewis2016BIO" />. Many oxygenase-expressing bacteria are able to degrade 1,4-dioxane to different degree under different physiological conditions.
 *[[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS) |'''Poly- and per-fluoroalkyl substances (PFAS).''']] Perfluoroalkyl compounds, particularly PFOA and PFOS, are not biodegradable under both aerobic and anaerobic conditions. However, poly-fluoroalkyl substances, like fluorotelomer alcohols (FTOHs) used as starting materials for many fluorotelomer-based products, are biodegradable and considered as precursors to perfluoroalkyl acids<ref>Parsons, J.R., Sáez, M., Dolfing, J. and de Voogt, P., 2008. Biodegradation of perfluorinated compounds. In Reviews of Environmental Contamination and Toxicology, Springer US, 196, 53-71. [https://doi.org/10.1007/978-0-387-78444-1_2 doi: 10.1007/978-0-387-78444-1_2]</ref>. A number of studies have demonstrated that FTOHs, including 8:2, 6:2 and 4:2 FTOHs, and FTOH-based surfactants like polyfluorinated alkyl phosphate esters and fluorotelomer sulfonates are comtabolically biotransformed into various shorter chain PFASs in soils, activated sludge, and by pure cultures<ref name= "Chu1998" /><ref name= "AlvarezC2001" /><ref name= "Parales1994" /><ref>Wang, N., Szostek, B., Buck, R.C., Folsom, P.W., Sulecki, L.M., Capka, V., Berti, W.R. and Gannon, J.T., 2005. Fluorotelomer alcohol biodegradation direct evidence that perfluorinated carbon chains breakdown. Environmental Science & Technology, 39(19), 7516-7528. [https://doi.org/10.1021/es0506760 doi: 10.1021/es0506760]</ref><ref>Kim, Y.M., Jeon, J.R., Murugesan, K., Kim, E.J. and Chang, Y.S., 2009. Biodegradation of 1, 4-dioxane and transformation of related cyclic compounds by a newly isolated Mycobacterium sp. PH-06. Biodegradation, 20(4), 511-519. [https://doi.org/10.1007/s10532-008-9240-0 doi: 10.1007/s10532-008-9240-0]</ref><ref>Wang, N., Liu, J., Buck, R. C., Korzeniowski, S. H., Wolstenholme, B. W., Folsom, P. W., Sulecki, L. M., 2011. 6:2 Fluorotelomer sulfonate aerobic biotransformation in activated sludge of waste water treatment plants. Chemosphere, 82(6), 853-858. [https://www.ncbi.nlm.nih.gov/pubmed/21112609 doi: 10.1016/j.chemosphere.2010.11.003]</ref>.

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 According to US Environmental Protection Agency (EPA), an emerging contaminant is defined as “a chemical or material characterized by a perceived, potential, or real threat to human health or the environment or by a lack of published health standards”<ref name= "USEPAEC"> US EPA Fact sheets about Emerging Contaminants. EPA 505-F-14-002. (Accessed October 27, 2016). [https://www.epa.gov/fedfac/emerging-contaminants-and-federal-facility-contaminants-concern US EPA Emerging Contaminants]</ref>. A number of technical fact sheets of emerging contaminants, including TCP, 1,4-dioxane, NDMA, and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) are available from the [https://www.epa.gov/fedfac/emerging-contaminants-and-federal-facility-contaminants-concern US EPA’s website] to guide  detection, analysis, and treatment of these emerging contaminants. Other emerging contaminants, such as poly-and per-fluoroalkyl substances (PFAS), pharmaceuticals and personal care products (PPCPs), and endocrine-disrupting compounds (EDCs) have also been the focus of intense research by scientists and engineers in recent years. Many of these emerging contaminants are also recalcitrant, but are subjected to cometabolic degradation by many different microbial strains under diverse conditions. Below is a brief description of studies reporting cometabolic degradation of selective emerging contaminants:
 *[[1,2,3-Trichloropropane | '''1,2,3-Trichlopropane (TCP).''']] TCP is a chlorinated hydrocarbon with high chemical stability. It is commonly detected in groundwater and soil, due to improper disposal. TCP is also a by-product or an intermediate in the production of various chemicals.  EPA has classified TCP as a suspected carcinogen to humans. An early study has showed that methane-oxidizing bacteria can degrade TCP cometabolically<ref>Bosma, T. and Janssen, D.B., 1998. Conversion of chlorinated propanes by Methylosinus trichosporium OB3b expressing soluble methane monooxygenase. Applied Microbiology and Biotechnology, 50(1), 105-112. [https://doi.org/10.1007/s002530051263 doi: 10.1007/s002530051263]</ref>. A more recent study also reported that some propane-oxidizing bacteria can cometabilize TCP effectively<ref> Chu, K. H., 2012. Biodegradation of 1,2,3-Trichloropropane, Texas Hazardous Waste Research Center Report, Project Report Number 060TAM2993.</ref>.
-*[[1,4-Dioxane |'''1,4-Dioxane.''']] 1,4-Dioxane is a likely human carcinogen and has been detected in groundwater at many sites. It is used as a solvent stabilizer in the manufacture and processing of paper, cotton, textile products, auto coolants, cosmetics, and shampoo. 1,4-dioxane can be degraded via both growth-linked<ref>Kim, Y.M., Jeon, J.R., Murugesan, K., Kim, E.J. and Chang, Y.S., 2009. Biodegradation of 1, 4-dioxane and transformation of related cyclic compounds by a newly isolated Mycobacterium sp. PH-06. Biodegradation, 20(4), 511-519. [https://doi.org/10.1007/s10532-008-9240-0 doi: 10.1007/s10532-008-9240-0]</ref><ref name= "Parales1994">Parales, R.E., Adamus, J.E., White, N. and May, H.D., 1994. Degradation of 1, 4-dioxane by an actinomycete in pure culture. Applied and Environmental Microbiology, 60(12), 4527-4530. [http://aem.asm.org/content/60/12/4527 Article]</ref> and cometabolic reactions<ref name= "Lewis2016BIO" />. Many oxygenase-expressing bacteria are able to degrade 1,4-dioxane to different degree under different physiological conditions.
+*[[1,4-Dioxane |'''1,4-Dioxane.''']] 1,4-Dioxane is a likely human carcinogen and has been detected in groundwater at many sites. It is used as a solvent stabilizer in the manufacture and processing of paper, cotton, textile products, auto coolants, cosmetics, and shampoo. 1,4-dioxane can be degraded via both growth-linked<ref>Kim, Y.M., Jeon, J.R., Murugesan, K., Kim, E.J. and Chang, Y.S., 2009. Biodegradation of 1, 4-dioxane and transformation of related cyclic compounds by a newly isolated Mycobacterium sp. PH-06. Biodegradation, 20(4), 511-519. [https://doi.org/10.1007/s10532-008-9240-0 doi: 10.1007/s10532-008-9240-0]</ref><ref name= "Parales1994">Parales, R.E., Adamus, J.E., White, N. and May, H.D., 1994. Degradation of 1, 4-dioxane by an actinomycete in pure culture. Applied and Environmental Microbiology, 60(12), 4527-4530. [https://doi.org/10.1128/aem.60.12.4527-4530.1994 doi:10.1128/aem.60.12.4527-4530.1994] [[media:1994-Parales-Degradation_of_1%2C4-Dioxane_by_an_Actinomycete_in_Pure_Culture.pdf| Article.pdf]]</ref></ref> and cometabolic reactions<ref name= "Lewis2016BIO" />. Many oxygenase-expressing bacteria are able to degrade 1,4-dioxane to different degree under different physiological conditions.
 *[[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS) |'''Poly- and per-fluoroalkyl substances (PFAS).''']] Perfluoroalkyl compounds, particularly PFOA and PFOS, are not biodegradable under both aerobic and anaerobic conditions. However, poly-fluoroalkyl substances, like fluorotelomer alcohols (FTOHs) used as starting materials for many fluorotelomer-based products, are biodegradable and considered as precursors to perfluoroalkyl acids<ref>Parsons, J.R., Sáez, M., Dolfing, J. and de Voogt, P., 2008. Biodegradation of perfluorinated compounds. In Reviews of Environmental Contamination and Toxicology, Springer US, 196, 53-71. [https://doi.org/10.1007/978-0-387-78444-1_2 doi: 10.1007/978-0-387-78444-1_2]</ref>. A number of studies have demonstrated that FTOHs, including 8:2, 6:2 and 4:2 FTOHs, and FTOH-based surfactants like polyfluorinated alkyl phosphate esters and fluorotelomer sulfonates are comtabolically biotransformed into various shorter chain PFASs in soils, activated sludge, and by pure cultures<ref name= "Chu1998" /><ref name= "AlvarezC2001" /><ref name= "Parales1994" /><ref>Wang, N., Szostek, B., Buck, R.C., Folsom, P.W., Sulecki, L.M., Capka, V., Berti, W.R. and Gannon, J.T., 2005. Fluorotelomer alcohol biodegradation direct evidence that perfluorinated carbon chains breakdown. Environmental Science & Technology, 39(19), 7516-7528. [https://doi.org/10.1021/es0506760 doi: 10.1021/es0506760]</ref><ref>Kim, Y.M., Jeon, J.R., Murugesan, K., Kim, E.J. and Chang, Y.S., 2009. Biodegradation of 1, 4-dioxane and transformation of related cyclic compounds by a newly isolated Mycobacterium sp. PH-06. Biodegradation, 20(4), 511-519. [https://doi.org/10.1007/s10532-008-9240-0 doi: 10.1007/s10532-008-9240-0]</ref><ref>Wang, N., Liu, J., Buck, R. C., Korzeniowski, S. H., Wolstenholme, B. W., Folsom, P. W., Sulecki, L. M., 2011. 6:2 Fluorotelomer sulfonate aerobic biotransformation in activated sludge of waste water treatment plants. Chemosphere, 82(6), 853-858. [https://www.ncbi.nlm.nih.gov/pubmed/21112609 doi: 10.1016/j.chemosphere.2010.11.003]</ref>.

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 ==Cometabolic Degradation of Emerging Contaminants and Other Trace Organics==
 According to US Environmental Protection Agency (EPA), an emerging contaminant is defined as “a chemical or material characterized by a perceived, potential, or real threat to human health or the environment or by a lack of published health standards”<ref name= "USEPAEC"> US EPA Fact sheets about Emerging Contaminants. EPA 505-F-14-002. (Accessed October 27, 2016). [https://www.epa.gov/fedfac/emerging-contaminants-and-federal-facility-contaminants-concern US EPA Emerging Contaminants]</ref>. A number of technical fact sheets of emerging contaminants, including TCP, 1,4-dioxane, NDMA, and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) are available from the [https://www.epa.gov/fedfac/emerging-contaminants-and-federal-facility-contaminants-concern US EPA’s website] to guide  detection, analysis, and treatment of these emerging contaminants. Other emerging contaminants, such as poly-and per-fluoroalkyl substances (PFAS), pharmaceuticals and personal care products (PPCPs), and endocrine-disrupting compounds (EDCs) have also been the focus of intense research by scientists and engineers in recent years. Many of these emerging contaminants are also recalcitrant, but are subjected to cometabolic degradation by many different microbial strains under diverse conditions. Below is a brief description of studies reporting cometabolic degradation of selective emerging contaminants:
-*[[1,2,3-Trichloropropane | '''1,2,3-trichlopropane (TCP).''']] TCP is a chlorinated hydrocarbon with high chemical stability. It is commonly detected in groundwater and soil, due to improper disposal. TCP is also a by-product or an intermediate in the production of various chemicals.  EPA has classified TCP as a suspected carcinogen to humans. An early study has showed that methane-oxidizing bacteria can degrade TCP cometabolically<ref>Bosma, T. and Janssen, D.B., 1998. Conversion of chlorinated propanes by Methylosinus trichosporium OB3b expressing soluble methane monooxygenase. Applied Microbiology and Biotechnology, 50(1), 105-112. [https://doi.org/10.1007/s002530051263 doi: 10.1007/s002530051263]</ref>. A more recent study also reported that some propane-oxidizing bacteria can cometabilize TCP effectively<ref> Chu, K. H., 2012. Biodegradation of 1,2,3-Trichloropropane, Texas Hazardous Waste Research Center Report, Project Report Number 060TAM2993.</ref>.
+*[[1,2,3-Trichloropropane | '''1,2,3-Trichlopropane (TCP).''']] TCP is a chlorinated hydrocarbon with high chemical stability. It is commonly detected in groundwater and soil, due to improper disposal. TCP is also a by-product or an intermediate in the production of various chemicals.  EPA has classified TCP as a suspected carcinogen to humans. An early study has showed that methane-oxidizing bacteria can degrade TCP cometabolically<ref>Bosma, T. and Janssen, D.B., 1998. Conversion of chlorinated propanes by Methylosinus trichosporium OB3b expressing soluble methane monooxygenase. Applied Microbiology and Biotechnology, 50(1), 105-112. [https://doi.org/10.1007/s002530051263 doi: 10.1007/s002530051263]</ref>. A more recent study also reported that some propane-oxidizing bacteria can cometabilize TCP effectively<ref> Chu, K. H., 2012. Biodegradation of 1,2,3-Trichloropropane, Texas Hazardous Waste Research Center Report, Project Report Number 060TAM2993.</ref>.
 *[[1,4-Dioxane |'''1,4-Dioxane.''']] 1,4-Dioxane is a likely human carcinogen and has been detected in groundwater at many sites. It is used as a solvent stabilizer in the manufacture and processing of paper, cotton, textile products, auto coolants, cosmetics, and shampoo. 1,4-dioxane can be degraded via both growth-linked<ref>Kim, Y.M., Jeon, J.R., Murugesan, K., Kim, E.J. and Chang, Y.S., 2009. Biodegradation of 1, 4-dioxane and transformation of related cyclic compounds by a newly isolated Mycobacterium sp. PH-06. Biodegradation, 20(4), 511-519. [https://doi.org/10.1007/s10532-008-9240-0 doi: 10.1007/s10532-008-9240-0]</ref><ref name= "Parales1994">Parales, R.E., Adamus, J.E., White, N. and May, H.D., 1994. Degradation of 1, 4-dioxane by an actinomycete in pure culture. Applied and Environmental Microbiology, 60(12), 4527-4530. [http://aem.asm.org/content/60/12/4527 Article]</ref> and cometabolic reactions<ref name= "Lewis2016BIO" />. Many oxygenase-expressing bacteria are able to degrade 1,4-dioxane to different degree under different physiological conditions.
 *[[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS) |'''Poly- and per-fluoroalkyl substances (PFAS).''']] Perfluoroalkyl compounds, particularly PFOA and PFOS, are not biodegradable under both aerobic and anaerobic conditions. However, poly-fluoroalkyl substances, like fluorotelomer alcohols (FTOHs) used as starting materials for many fluorotelomer-based products, are biodegradable and considered as precursors to perfluoroalkyl acids<ref>Parsons, J.R., Sáez, M., Dolfing, J. and de Voogt, P., 2008. Biodegradation of perfluorinated compounds. In Reviews of Environmental Contamination and Toxicology, Springer US, 196, 53-71. [https://doi.org/10.1007/978-0-387-78444-1_2 doi: 10.1007/978-0-387-78444-1_2]</ref>. A number of studies have demonstrated that FTOHs, including 8:2, 6:2 and 4:2 FTOHs, and FTOH-based surfactants like polyfluorinated alkyl phosphate esters and fluorotelomer sulfonates are comtabolically biotransformed into various shorter chain PFASs in soils, activated sludge, and by pure cultures<ref name= "Chu1998" /><ref name= "AlvarezC2001" /><ref name= "Parales1994" /><ref>Wang, N., Szostek, B., Buck, R.C., Folsom, P.W., Sulecki, L.M., Capka, V., Berti, W.R. and Gannon, J.T., 2005. Fluorotelomer alcohol biodegradation direct evidence that perfluorinated carbon chains breakdown. Environmental Science & Technology, 39(19), 7516-7528. [https://doi.org/10.1021/es0506760 doi: 10.1021/es0506760]</ref><ref>Kim, Y.M., Jeon, J.R., Murugesan, K., Kim, E.J. and Chang, Y.S., 2009. Biodegradation of 1, 4-dioxane and transformation of related cyclic compounds by a newly isolated Mycobacterium sp. PH-06. Biodegradation, 20(4), 511-519. [https://doi.org/10.1007/s10532-008-9240-0 doi: 10.1007/s10532-008-9240-0]</ref><ref>Wang, N., Liu, J., Buck, R. C., Korzeniowski, S. H., Wolstenholme, B. W., Folsom, P. W., Sulecki, L. M., 2011. 6:2 Fluorotelomer sulfonate aerobic biotransformation in activated sludge of waste water treatment plants. Chemosphere, 82(6), 853-858. [https://www.ncbi.nlm.nih.gov/pubmed/21112609 doi: 10.1016/j.chemosphere.2010.11.003]</ref>.

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 ==Cometabolic Degradation of Emerging Contaminants and Other Trace Organics==
 According to US Environmental Protection Agency (EPA), an emerging contaminant is defined as “a chemical or material characterized by a perceived, potential, or real threat to human health or the environment or by a lack of published health standards”<ref name= "USEPAEC"> US EPA Fact sheets about Emerging Contaminants. EPA 505-F-14-002. (Accessed October 27, 2016). [https://www.epa.gov/fedfac/emerging-contaminants-and-federal-facility-contaminants-concern US EPA Emerging Contaminants]</ref>. A number of technical fact sheets of emerging contaminants, including TCP, 1,4-dioxane, NDMA, and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) are available from the [https://www.epa.gov/fedfac/emerging-contaminants-and-federal-facility-contaminants-concern US EPA’s website] to guide  detection, analysis, and treatment of these emerging contaminants. Other emerging contaminants, such as poly-and per-fluoroalkyl substances (PFAS), pharmaceuticals and personal care products (PPCPs), and endocrine-disrupting compounds (EDCs) have also been the focus of intense research by scientists and engineers in recent years. Many of these emerging contaminants are also recalcitrant, but are subjected to cometabolic degradation by many different microbial strains under diverse conditions. Below is a brief description of studies reporting cometabolic degradation of selective emerging contaminants:
-*[[1,2,3-Trichloropropane | '''1,2,3-trichlopropane (TCP).''']] TCP is a chlorinated hydrocarbon with high chemical stability. It is commonly detected in groundwater and soil, due to improper disposal. TCP is also a by-product or an intermediate in the production of various chemicals.  EPA has classified TCP as a suspected carcinogen to humans. An early study has showed that methane-oxidizing bacteria can degrade TCP cometabolically<ref>Bosma, T. and Janssen, D.B., 1998. Conversion of chlorinated propanes by Methylosinus trichosporium OB3b expressing soluble methane monooxygenase. Applied Microbiology and Biotechnology, 50(1), 105-112. [https://doi.org/10.1007/s002530051263 doi: 10.1007/s002530051263]</ref>. A recent study also reported that some propane-oxidizing bacteria can cometabilize TCP effectively<ref> Chu, K. H., 2012. Biodegradation of 1,2,3-Trichloropropane, Texas Hazardous Waste Research Center Report, Project Report Number 060TAM2993.</ref>.
+*[[1,2,3-Trichloropropane | '''1,2,3-trichlopropane (TCP).''']] TCP is a chlorinated hydrocarbon with high chemical stability. It is commonly detected in groundwater and soil, due to improper disposal. TCP is also a by-product or an intermediate in the production of various chemicals.  EPA has classified TCP as a suspected carcinogen to humans. An early study has showed that methane-oxidizing bacteria can degrade TCP cometabolically<ref>Bosma, T. and Janssen, D.B., 1998. Conversion of chlorinated propanes by Methylosinus trichosporium OB3b expressing soluble methane monooxygenase. Applied Microbiology and Biotechnology, 50(1), 105-112. [https://doi.org/10.1007/s002530051263 doi: 10.1007/s002530051263]</ref>. A more recent study also reported that some propane-oxidizing bacteria can cometabilize TCP effectively<ref> Chu, K. H., 2012. Biodegradation of 1,2,3-Trichloropropane, Texas Hazardous Waste Research Center Report, Project Report Number 060TAM2993.</ref>.
 *[[1,4-Dioxane |'''1,4-Dioxane.''']] 1,4-Dioxane is a likely human carcinogen and has been detected in groundwater at many sites. It is used as a solvent stabilizer in the manufacture and processing of paper, cotton, textile products, auto coolants, cosmetics, and shampoo. 1,4-dioxane can be degraded via both growth-linked<ref>Kim, Y.M., Jeon, J.R., Murugesan, K., Kim, E.J. and Chang, Y.S., 2009. Biodegradation of 1, 4-dioxane and transformation of related cyclic compounds by a newly isolated Mycobacterium sp. PH-06. Biodegradation, 20(4), 511-519. [https://doi.org/10.1007/s10532-008-9240-0 doi: 10.1007/s10532-008-9240-0]</ref><ref name= "Parales1994">Parales, R.E., Adamus, J.E., White, N. and May, H.D., 1994. Degradation of 1, 4-dioxane by an actinomycete in pure culture. Applied and Environmental Microbiology, 60(12), 4527-4530. [http://aem.asm.org/content/60/12/4527 Article]</ref> and cometabolic reactions<ref name= "Lewis2016BIO" />. Many oxygenase-expressing bacteria are able to degrade 1,4-dioxane to different degree under different physiological conditions.
 *[[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS) |'''Poly- and per-fluoroalkyl substances (PFAS).''']] Perfluoroalkyl compounds, particularly PFOA and PFOS, are not biodegradable under both aerobic and anaerobic conditions. However, poly-fluoroalkyl substances, like fluorotelomer alcohols (FTOHs) used as starting materials for many fluorotelomer-based products, are biodegradable and considered as precursors to perfluoroalkyl acids<ref>Parsons, J.R., Sáez, M., Dolfing, J. and de Voogt, P., 2008. Biodegradation of perfluorinated compounds. In Reviews of Environmental Contamination and Toxicology, Springer US, 196, 53-71. [https://doi.org/10.1007/978-0-387-78444-1_2 doi: 10.1007/978-0-387-78444-1_2]</ref>. A number of studies have demonstrated that FTOHs, including 8:2, 6:2 and 4:2 FTOHs, and FTOH-based surfactants like polyfluorinated alkyl phosphate esters and fluorotelomer sulfonates are comtabolically biotransformed into various shorter chain PFASs in soils, activated sludge, and by pure cultures<ref name= "Chu1998" /><ref name= "AlvarezC2001" /><ref name= "Parales1994" /><ref>Wang, N., Szostek, B., Buck, R.C., Folsom, P.W., Sulecki, L.M., Capka, V., Berti, W.R. and Gannon, J.T., 2005. Fluorotelomer alcohol biodegradation direct evidence that perfluorinated carbon chains breakdown. Environmental Science & Technology, 39(19), 7516-7528. [https://doi.org/10.1021/es0506760 doi: 10.1021/es0506760]</ref><ref>Kim, Y.M., Jeon, J.R., Murugesan, K., Kim, E.J. and Chang, Y.S., 2009. Biodegradation of 1, 4-dioxane and transformation of related cyclic compounds by a newly isolated Mycobacterium sp. PH-06. Biodegradation, 20(4), 511-519. [https://doi.org/10.1007/s10532-008-9240-0 doi: 10.1007/s10532-008-9240-0]</ref><ref>Wang, N., Liu, J., Buck, R. C., Korzeniowski, S. H., Wolstenholme, B. W., Folsom, P. W., Sulecki, L. M., 2011. 6:2 Fluorotelomer sulfonate aerobic biotransformation in activated sludge of waste water treatment plants. Chemosphere, 82(6), 853-858. [https://www.ncbi.nlm.nih.gov/pubmed/21112609 doi: 10.1016/j.chemosphere.2010.11.003]</ref>.