Biodegradation cometabolic

Aerobic biodegradation of trichloroethylene occurs by cometabolism with aromatie eompounds (Ensley 1991) and thus requires a cosubstrate such as phenol (Nelson et al. 1987, 1988) or toluene (Fan and Scow 1993). Trichloroethylene degradation by toluene-degrading baeteria has been demonstrated in the presence, but not absence, of toluene (Mu and Scow 1994). Isoprene, a structural analog of trichloroethylene, has also been used as a cosubstrate for triehloroethylene oxidation by some bacteria (Ewers et al. 1990). One source of inhibition of degradation in the absence of cosubstrate may be the toxieity of triehloroethylene itself to indigenous bacteria. 

Hernandez BS, JJ Arensdorf, DD Focht (1995) Catabolic characteristic of biphenyl-ntilizing isolates which cometabolize PCBs. Biodegradation 6 75-82. 

Alexander55 identifies six major kinds of biodegradation mineralization, cometabolism, detoxification, transtoxification, activation, and defusing. Table 20.10 describes each of these processes and gives examples. 

When a compound is cometabolized (degraded but not used as a nutrient), a second-order biodegradation coefficient can be used to estimate, kB ... 

Electron donors—In direct biodegradation pathways, the contaminant acts as the electron donor or substrate. However, during cometabolic degradation, a different electron donor is metabolized, resulting in the consequential oxidation of the contaminant. In some contaminated plumes, other electron donors, such as other constituents of gasoline, may also be present. In cases where they are not, and cometabolic degradation pathways are desired, electron donors may be added. 

A full-scale cleanup was performed using in situ bioremediation to treat MTBE and BTEX at a service station in Massachusetts. Soil at the site consists of a layer of sand and gravel underlain by peat, silt, and clay. The in situ bioremediation system consisted of 12 injection wells and two butane injection panels used to stimulate cometabolic aerobic biodegradation of the contaminants in groundwater. The system was operated between October 2000 and January 2001. MTBE concentrations were reduced from 370 to 12 pg/L and BTEX contamination in groundwater was reduced by approximately two orders of magnitude during the 4-month period.74... 

Hyman, M., Microbial cometabolism of MTBE, MTBE Biodegradation Workshop, Cincinnati, OH, February 1-3, 2000. 

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. 

Biological. A Nocardia sp., growing on. n-octadecane, biodegraded propylbenzene to phenylacetic acid (Davis and Raymond, 1981). Propylbenzene was cometabolized by a strain of Micrococcus cerificans to cinnamic acid (Fitter and Chudoba, 1990). 

Higher-molecular-weight PAHs, such as pyrene, benzo(a)pyrene, and benzo(e)-pyrene, exhibit a high resistance to biodegradation. PAHs with three or more condensed rings tend not to act as a sole substrate for microbial growth and require cometabolic transformations. Neilson and Allard (1998) report a cometabolic reaction of pyrene, 1,2-benzanthracene, 3,4-benzopyrene, and phenanthrene in the presence of either naphthalene or phenanthrene. However, the cometabolic reactions are very slow in natural ecosystems. 

Biodegradation by enzymes of genetically engineered strains Biooxidation after reductive or oxidative biodechlorination Biooxidation after reductive or oxidative biodechlorination Biooxidation by cometabolization with methane or ammonium... 

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. 

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

In pure cultures of microorganisms, the products of cometabolism tend to accumulate and often do not undergo further degradation. However, in mixed cultures, which are the norm for environmental systems, they may serve as substrates for other organisms so that complete biodegradation results. Therefore, studies of biodegradation in pure cultures are usually of limited utility in predicting what happens in the environment. 

Chang M-K, Voice TC, Criddle CS. 1993. Kinetics of competitive inhibition and cometabolism in the biodegradation of benzene, toluene, and p-xylene by two Pseudomonas isolates. Biotechnol Bioeng 41(11) 1057-1065. 

Cometabolism, which increases the biodegradation rate of the multiple targeted compounds. 

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