Cometabolic process

Weber and Adams (1995) observed the rapid reduction of the azo dye Disperse Blue 79 chemically as well as in three anoxic sediment/ water systems. Half lives were on the order of minutes to hours. An initial rapid loss of the dye was followed by a much slower rate of transformation, and, most probably, chemical or cometabolic processes were responsible for transformation. 

In five sifes, TBA biodegradation was very slow (site 10) or not confirmed affer a second addition of TBA (sites 5, 6, 12, 13). The case of sites 5 and 6 is interesting because the same behavior was observed in the presence of MTBE and a similar explanation involving a cometabolic process could be proposed (see above, under MTBE biodegradability). 

Availability in inorganic nutrients and additional organic material for cometabolic processes... 

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. 

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. 

Once the methanotroph-containing CSR has been established, we expect it can cometabolically oxidize some of the TCE incidental to the use of the primary substrate, methane. The rate of TCE biotransformation is dictated by the effectiveness of the methane mono-oxygenase for interacting with TCE rather than methane. This enzymatic processing of TCE can be described using a Michaelis-Menten expression ... 

Axenic bacterial cultures that grow on HMW PAHs of four or more fused rings have been reported. Many studies also suggest that this breadth includes cometabolism or fortuitous metabolism. This is a process in which enzymes responsible for the initial oxidation of a particular PAH fortuitously oxidize other, higher-molecular-weight PAHs, even though these latter substrates may not ultimately be used as a source of carbon and energy for the cells. In addition,... 

Xenobiotic compounds are usually attacked by enzymes whose primary function is to react with other compounds, a process that provides neither carbon nor energy called cometabolism. Cometabolism usually involves relatively small modifications of the substance that is cometabolized (the secondary substrate), compared to the primary substrate. The enzymes that carry out cometabolism tend to be relatively nonspecific. As an environmentally significant example of cometabolism, at least one strain of bacteria degrades trichloroethylene with an enzyme system that acts predominantly on phenol. The enzyme activity can be induced by exposure to phenol, after which it acts on trichloroethylene. 

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