Cometabolism of chlorinated

Alvarez-Cohen, L., and G. E. J. Speitel, Kintics of aerobic cometabolism of chlorinated solvents , Biodegradation, 12, 105-126 (2001). 

Ensign, S. A., Hyman, M. R. Arp, D. J. (1992). Cometabolic degradation of chlorinated alkenes by alkene monooxygenase in a propylene-grown Xanthobacter strain. Applied and Environmental Microbiology, 58, 3038-46. 

Semprini L,McCarty PL (1992) Comparison between model simulations and field results for in-situ biorestoration of chlorinated aliphatics. Part 2. Cometabolic transformations. Ground Water 30 37-44... 

Omori T, Kimura T, Kodama T (1987) Bacterial cometabolic degradation of chlorinated paraffins. Appl Microbiol Biotechnol 25 553-557... 

Corcho D, Watkinson RL, Lerner DN (2000) Cometabolic degradation of MTBE by a cyclohexane-oxidizing bacteria. Proceedings of the Second International Conference on Remediation of Chlorinated and Recalcitrant Compounds, Monterey, CA, May 22-25, 2000. Batelle Press, Columbus... 

Hyman MR, Kwon P, O Reilly KT (1998) Cometabolism of MTBE by alkane-utUizing microorganisms. In Wickramanayake GB, Hinchee RE (eds) The First International Conference on Remediation of Chlorinated and Recalcitrant Compounds. Battelle, Monterey, California, May 18-21, p 321... 

Chlorinated ethenes are subject to a variety of microbial degradation processes that include reductive dechlorination (Vogel et al., 1987 Maymo-Gatell et al., 1997), aerobic oxidation, anaerobic oxidation (Bradley and Chapelle, 1996), and anaerobic cometabolism (McCarty and Semprini, 1994). Both, laboratory studies (Bradley and Chapelle, 1998), and field studies (Chapelle and Bradley, 2000) show that the efficiency of chlorinated ethene biodegradation depends on ambient redox conditions. Therefore, reliable tools to measure the redox conditions are crucial to imderstand and even predict chlorinated ethene degradation. 

Chlorinated benzoic acids have been shown to be intermediates in the biodegradation of several chlorinated aromatic compounds, for example, 4-chlorobenzoic acid is formed in the biodegradation of both polychlorinated biphenyls [103]. Mixed microbial cultures, which have been studied by a number of groups under aerobic conditions, can degrade a wide range of chlorinated benzoic acids, including 2-, 3- and 4-chlorobenzoic acid as well as 3,4-dichloro- and 2,4-dichlorobenzoic acid [104]. By contrast, under anaerobic conditions, only reductive dechlorination of meta-substituted benzoic acids has been observed [49,105,106]. Cometabolism of chlorobenzoic acids in the presence of unsubstituted benzoic adds leads to the formation of the corresponding... 

Herbicides, 2,4-D and 2,4,5-T are structurally related, the latter having an extra chlorine atom at position 5. Unlike 2,4-D, 2,4,5-T is poorly biodegradable, and persists for long periods, hence constituting a pollution problem [155]. Cometabolism of 2,4,5-T by Brevibacterium sp. resulted in the formation of the product, tentatively identified as 3,5-dichlorocatechol. Bacterial cometabohsm of 2,4,5-T was also described by Rosenberg and Alexander [156], who proposed a degradation pathway of 2,4,5-T in soil [157]. Reductive dechlorination of 2,4,5-T by anaerobic microorganisms was described by Suflita et al. [130]. 

The third most common biodegradation pathway for chlorinated hydrocarbons is cometabolism via enzymatic reactions occurring fortuitously with oxidation of compounds such as methane or toluene. These three pathways are, of course, complicated by the fact that 1) each can only occur under specific chemical conditions 2) the dominant pathway changes as the source of electron donor and/or acceptor (both anthropogenic and indigenous) is reduced and 3) There are several different isomers, and other compounds of chlorinated hydrocarbons, that can enter these pathways from biotic or abiotic processes. In other words, it is a complicated process. 

Degradation of chlorinated compounds under aerobic cometabolic degradation can occur fortuitously and that is because the implicated enzymes in this process ean be used for auxiliary substrates that are bacterial growth substrates (Tiehm and Schmidt, 2011). It has been reported that under aerobic conditions, chlorinated ethenes, with the exception of... 

Frascari, D., Pinelli, D., Nocentini, M., Zannoni, A., Fedi, S., Baleani, E., Zannoni, D., Fameti, A., Battistelli, A. 2006. Long-term aerobic cometabolism of a chlorinated solvent mixture by vinyl chloride-, methane- and propane-utilizing biomasses. J Hazard Mater. 138(1) 29-39. 

Cometabolism refers to the degradation of the chlorinated solvent as a by-product of the degradation of other substrates by microorganisms, and does not benefit the microorganism. As the degree of dechlorination decreases, the cometabolism rates increase. Thus, less oxidized or chlorinated solvents such as chlorinated ethenes (excluding PCE) biodegrade more favorably under aerobic conditions. 

The BAT system operates based on principles of aerobic cometabolism. In cometabohsm, enzymes that the microbes produce in the process of consuming one particular compound (e.g., phenol) have the collateral effect of transforming another compound that normally resists biodegradation (e.g., chlorinated ethenes, especially lesser chlorinated ethenes such as dichloroethene or vinyl chloride). The BAT system operates under these principles by sorbing the chlorinated compounds from a vapor stream onto powdered activated carbon (PAC) where they are cometabolically transformed into a combination of end products, including new biomass, carbon dioxide, inorganic salts, and various acids. 

With the recent finding that PCE can be aerobically cometabolized [34], it has now been shown that except for carbon tetrachloride, all of the major chlorinated ethenes, ethanes, and methanes found in groundwater may be biode-... 

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