Biotransformation and Biodegradation

Second, microbial chemical transformations are accomplished by means of enzymes, proteins that act as catalysts. Catalysts bind with reactants and hold them in such an orientation that they more readily react. The products of the reaction are then released, leaving the catalyst ready to facilitate another transformation. (It is possible for an enzyme to be destroyed if a chemical mimics the proper substrate sufficiently to bind, but fails to react and subsequently release from the enzyme.) Because each enzyme is produced in response to a section of the genetic code (DNA) in the organism and many enzymes are extremely specific, it is possible that some strains of a species of bacteria may accomplish a certain chemical transformation while other individuals cannot. By using modern techniques of molecular biology, scientists can insert specific biotransformation capabilities into bacteria by means of genetic transfer. This procedure is easiest if the genetic material is associated with plasmids, which are small circular molecules of DNA that can exist independently within a bacterial cell. 

FIGURE 2-24 Several examples of organic compounds biodegraded by aerobic microorganisms, and their associated biodegradation reactions. Each of the reactions shown involves the oxidation of the organic compound. 

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Kuo, C. and Genthner, B., Effect of added heavy metal ions on biotransformation and biodegradation of 2-chlorophenol and 3-chlorobenzoate in anaerobic bacterial consortia, Appl Environ Microbiol, 62 (7), 2317-2323, 1996. 

The ultimate fate of those PAHs that accumulate in sediments is believed to be biotransformation and biodegradation by benthic organisms (USEPA 1980). PAHs in aquatic sediments, however, degrade very slowly in the absence of penetrating radiation and oxygen (Suess 1976), and may... 

Razo-Flores, E., Lettinga, G., and Field. J. A. Biotransformation and biodegradation of selected nitroaromatics under anaerobic conditions, Biotechnol Prog., 15(3) 358-365,1999. 

Portier, R.J., Fujisalo, K. (1988) Enhanced biotransformation and biodegradation of polychlorinated biphenyls in the presence of aminopolysaccharides. In Aquatic Toxicoloty and Hoard Assessment 10th volume, ASTM STP 971. Adams, W.J., Chapman, G.A., Landis, W.G., Eds. American Society for Testing and Materials, pp. 517-527, Philadelphia. 

Willie J. G. M. Peijnenburg and Jiri Damborsky, Biodegradability Prediction. Proceedings of the NATO Advanced Research Workshop on QSAR Biodegradation II QSARs for Biotransformation and Biodegradation, Luhacovice, Czech Republic, 2-3 May 1996, in NATO ASI Series, Ser. 2, Vol. 23, Kluwer, Dordrecht, 1996. 

The examples provided above give only a brief overview of the variety of enzymatic functions that alter, biotransform, and biodegrade xenobiotics. In many instances numerous enzymes are known, as in the case of the mixed function oxidases. In order to provide a concrete example of a system of detoxification enzymes that is widely distributed, we have chosen the organophosphate acid anhydrolases — enzymes that may aid in the understanding of organophosphate intoxication and may also provide a means for the detoxification and bioremediation of these materials. 

Another important aspect of the toxicological chemistry of water pollutants involves biotransformations and biodegradation of pollutants. Some of the compounds found as markers of water... 

Razo-Flores E (1997) Biotransformation and biodegradation of N-substituted aromatics in metha-nogenic granular sludge. PhD thesis, Wageningen Agriculture University, The Netherlands, http //edepot. wur. nl/199864... 

BIOTRANSFORMATION AND BIODEGRADATION 171 TABLE 2.7 Aerobic Biodegradation Rates Observed in Incubations of River Water Samples" ... 

BIOTRANSFORMATION AND BIODEGRADATION TABLE 2.9 Regression Equations for Estimating BCF for Fish 179... 

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