Xenobiotics, degradation

Basta T, A Keck, J Klein, A Stolz (2004) Detection and characterization of conjugative plasmids in xenobiotic-degrading Sphingomonas strains. J Bacteriol 186 3862-3872. 

Uchida E, T Ouchi, Y Suzuki, T Yoshida, H Habe, I Yamaguchi, T Omori, H Nojiri (2005) Secretion of bacterial xenobiotic-degrading enzymes from transgenic plants by an apoplastic expression system applicability for phytoremediation. Environ Sci Technol 39 7671-7677. 

Widada, J. Nojiri, H. Omori,T. Recent developments in molecular techniques for identification and monitoring of xenobiotic-degrading bacteria and their catabolic genes in bioremediation. Appl. Microbiol. Biotechnol. 2002,60,45-59. 

The study of the degradation pathways in fungi for PPCPs is relatively recent and not fully developed. In general, the most studied xenobiotic degradation pathways in fungi are those related to PAHs [61]. As PPCPs present aromatic structures it is... 

Okey R. W. and Stensel H. D. (1996) A QSBR development procedure for aromatic xenobiotic degradation by unacclimated bacteria. Water Environ. Res. 65, 772-780. 

Evolutionary events also occur within multispecies toxicity tests. Species or strains resistant to xenobiotics do arise. Simple microbial microcosms (chemostats) are often used to force the evolution of new metabolic pathways for pesticide and xenobiotic degradation. 

The University of Minnesota has been adding to the Biocatalysis/Biodegradation Database [Ellis et al. 2003] since the early 1990s. It includes 144 pathways of microbial metabolism, mostly for xenobiotic degradation. 

Busse, H.-J., T. El-Banna, H. Oyaizu, and G. Auling. 1991. Identification of xenobiotic-degrading isolates from the beta subclass of the Proteobacteria by a polyphasic approach including 16S rRNA sequencing. Int. J. Syst. Bacteriol. 42 19-26. 

The success of this technique has hinged upon the knowledge that many xenobiotic-degrading genes are resident on extrachromosomal pieces of DNA called plasmids (23). Pesticide degradation plasmids were first described for 2,4-D and MCPA (29-311. Plasmids are also known to code for enzymes degrading 2,4,5-T (12.) and the OP insecticide diazinon (2Z) Several copies of a specific plasmid occur within an individual cell, and plasmids can be transferred from a donor cell to a recipient cell. 

CYP105AB3 (P450 MoxA) Nonomuraea recticatena 2Z36 Nonspecific, e.g., compactin, lucifer-ase and oleanolic acid hydroxylation in xenobiotic degradation and natural product synthesis [780]... 

The use of P450s in artificial cascade reactions is a rather unexplored research field, and corresponding reports are still very rare in the literature. However, their ability to oxyfunctionalize cheap starting molecules to form valuable compounds, combined with their broad natural functions as essential components in xenobiotics degradation and biosynthesis of secondary metabolites, makes P450 enzymes potential candidates for multi-enzyme processes. 

Metabolic engineering may be used to solve these problems, and it furthermore offers the possibility to constmct completely novel xenobiotics degrading pathways through recruitment of enzymes from different organisms. 

Once a reaction has been performed, we have to establish whether the reaction took the desired course, and whether we obtained the desired structure. For our knowledge of chemical reactions is stiU too cursory there are so many factors influencing the course of a chemical reaction that we are not always able to predict which products will be obtained, whether we also shall obtain side reactions, or whether the reaction will take a completely different course than expected. Thus we have to establish the structure of the reaction product (Figure 1-4). A similar problem arises when the degradation of a xenobiotic in the environment, or in a living organism, has to be established. 

Walker WW, Cripe CR, Pritchard PH, et al. 1988. Biological and abiotic degradation of xenobiotic compounds in in vitro estuarine water and sediment/water systems. Chemosphere 17 2255-2270. 

Many xenobiotics, both synthetic and natnrally occuring, are lipophilic esters. They can be degraded to water-soluble acids and bases by hydrolytic attack. Two important examples of esteratic hydrolysis in ecotoxicology now follow ... 

A xenobiotic is said to be stored when it is not available to sites of metabolism or action and is not available for excretion. In other words, it is held in an inert position from a toxicological point of view, where it is not able to express toxic action or to be acted upon by enzymes. A xenobiotic is stored when it is located in a fat depot (adipose tissue), bound to an inert protein or other cellular macromolecule, or simply held in a membrane that does not have any toxicological function (i.e., it does not contain or represent a site of toxic action, neither does it contain enzymes that can degrade the xenobiotic). 

It has been shown that a combination of photolytic and biotic reactions can result in enhanced degradation of xenobiotics in municipal treatment systems, for example, of chlorophenols (Miller et al. 1988a) and benzo[a]pyrene (Miller et al. 1988b). Two examples illustrate the success of a combination of microbial and photochemical reactions in accomplishing the degradation of widely different xenobiotics in natural ecosystems. Both of them involved marine bacteria, and it therefore seems plausible to assume that such processes might be especially important in warm-water marine enviromnents. 

It is experimentally difficult to obtain numerical estimates of the total number of bacteria present in seawater, and the contribution of ultramicroorganisms that have a small cell volume and low concentrations of DNA may be seriously underestimated. Although it is possible to evaluate their contribution to the uptake and mineralization of readily degraded compounds such as amino acids and carbohydrates, it is more difficult to estimate then-potential for degrading xenobiotics at realistic concentrations. 

The fate of xenobiotics in many environments is therefore significantly determined by the degradative activity of anaerobic bacteria. 

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