Pesticides microbial metabolism

Munnecke DM, LM Johnson, HW Talbot, S Barik (1982) Microbial metabolism and enzymology of selected pesticides. In Biodegradation and Detoxification of Environmental Pollutants (Ed AM Chrakrabarty), pp. 1-32. CRC Press, Boca Raton, FL. 

MacRae, I.C. Microbial metabolism of pesticides and stmcturally related compounds. Rev. Environ. Contam. Toxicol, 109 2-87, 1989. 

The microbial metabolic process is the major mechanism for the transformation of toxic organic chemicals in the subsurface environment. The transformation process may be the result of a primary metabolic reaction, when the organic molecule is degraded by a direct microbial metabolism. Alternatively, the transformation process may be an indirect, secondary effect of the microbial population on the chemical and physical properties of the subsurface constituents. Bollag and Liu (1990), considering behavior of pesticides, defined five basic processes involved in microbially mediated transformation of toxic organic molecules in the soil upper layer environment. These processes are described next. 

Okey, R.W., Bogan, R.H. (1965) Apparent involvement of electronic mechanisms in limiting microbial metabolism of pesticides. J. Water Pollut. Control Eed. 37, 692-712. 

Pesticides are susceptible to a variety of transformations in the environment, including both chemical degradation and microbial metabolism. Microbial transformations are cataly2ed exclusively by enzymes, whereas chemical transformations are mediated by a variety of organic and inorganic compounds. Many pesticide transformations can occur either chemically or biologically. Consequendy, most pesticide dissipation studies include sterile treatments to... 

Bollag J.-M. (1982) Microbial metabolism of pesticides. In Microbial Transformations of Bioactive Compounds (ed. J. P. Rosazza). CRC Press, Boca Raton, FL, vol. 2,... 

The microbial metabolism of pesticides has often been subdivided into 2 distinct classes. The first of these is termed simply "catabolism". This process often results in the mineralization of some portion of an organic compound via enzymatic pathways to simple products of universal currency (C02, NH3). In some cases, one portion of the molecule may be mineralized and another portion may accumulate in soil. This is true for the soil microbial degradation of carbofuran (42,43). Therefore, catabolism should not be equated with mineralization or complete destruction of a pesticide. It should be pointed out, however, that mineralization of a pesticide in soil Is nearly always a consequence of microbial activity (44). The key to understanding catabolism is that it is primarily a process driven by the microbial quest for energy. Therefore, catabolism has come to be equated with utilization of a pesticide as an energy source and thus a growth substrate (40,41). Catabolism is most commonly linked to the conversion of pesticides into carbon skeleton... 

Another important variable that determines the microbial metabolism of soil-applied pesticides is the availability of the chemical to the microbial systems degrading it. The hydrolysis product and parent pesticide should be available to microbes so as to exert their toxicity or provide nutrient value. The lack of availability of some chemicals may result in resistance to microbial adaptation. 

Implications of Mobility on the Availability and Degradation of Pesticides in Soil. Repeated application of 2,4-dichlorophenol, p-nitrophenol, and salicylic acid (as observed in current studies) and carbofuran phenol (20) has induced enhanced microbial degradation of their parent compounds. Rf values of these hydrolysis products indicate intermediate to high mobility in soils. The p-nitrophenol, 2,4-dichlorophenol, and salicylic acid were utilized as energy sources by microbes, and their availability in soil may contribute to the induction of rapid microbial metabolism. Carbofuran phenol did not serve as a microbial substrate but also enhanced the degradation of its parent compound, carbofuran (20). Carbofuran phenol is freely available in anaerobic soils, but the significance of its availability is yet to be understood. 

Pesticides—Biodegradation—Congresses. 2. Microbial metabolism—Congresses. 

Microbial reduction of toxic organics is carried out by reduction enzymes. Major reduction reactions of selected toxic organics are shown in Table 13.5. The reduction of the nitro group to amine involves the formation of a nitro and a hydroxyamino group. This type of reduction reaction occurs during the microbial metabolism of various pesticides. Organophosphorous pesticides such as para-thion, paraoxon, or fenitrothion are often reduced to nontoxic amino compounds (Miyamoto et al., 1966 Matsumura and Benezet, 1978). 

Hansch and Leo [13] described the impact of Hpophihdty on pharmacodynamic events in detailed chapters on QSAR studies of proteins and enzymes, of antitumor drugs, of central nervous system agents as well as microbial and pesticide QSAR studies. Furthermore, many reviews document the prime importance of log P as descriptors of absorption, distribution, metabolism, excretion and toxicity (ADMET) properties [5-18]. Increased lipophilicity was shown to correlate with poorer aqueous solubility, increased plasma protein binding, increased storage in tissues, and more rapid metabolism and elimination. Lipophilicity is also a highly important descriptor of blood-brain barrier (BBB) permeability [19, 20]. Last, but not least, lipophilicity plays a dominant role in toxicity prediction [21]. 

Table 15.2 Oxidation reactions in microbial pesticide metabolism (Bollag and Liu 1990)...

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