Biotic transformation reactions

Alterations may include transformation, degradation, and changes in speciation or ionization. Transformation occurs when a contaminant is chemically altered by the addition of oxygen, hydrogen, or nitrogen, or is combined with or bound to another chemical. Abiotic transformations may include chemical oxidations or reductions in aerobic or anaerobic environments, respectively. Biotic transformations may be carried out by bacteria and fungi in the environment, or may take place within the bodies of plants and animals. Transformations may either make the chemical more or less toxic, depending on the reaction involved. If the chemical is broken down... 

Reactions affecting the environmental fate of halogenated one- and two-carbon compounds can be broadly classified as substitutions, dehydrohalogenatdons, oxidations, and reductions [4]. These reactions can be either abiotic or biotic. Dehydrohalogenations are typically abiotic, while oxidations in dark environments are mostly biotic. Substitutions and reductions can be either biotic or abiotic. With some notable exceptions, abiotic transformations tend to be slow. Biotic transformations can be rapid when the microorganisms, that nthesize reactive enzymes or cofactors, are present in suffident numbers. 

Transformation reactions concern chemicals in the environment by abiotic (chemical and photochemical) and biotic (microbial) pathways. 

The operation of these hydrolytic reactions is independent of the oxygen concentration of the system so that—in contrast to biotic degradation and transformation—these reactions may occur effectively under both aerobic and anaerobic conditions. 

Exploratory experiments with dictyotene and suspensions of male gametes of E. siliculosus showed a significantly enhanced production of the 6-butylcyclohepta-2,4-dienol and its isomers. This indicates that a biological degradative pathway does exist and that this pathway follows the same oxidative sequence as the abiotic route. However, final conclusions about the biotic contribution to the pheromone transformation cannot be drawn before careful analysis of the degree of enantioselectiv-ity of the biotic reaction. 

The abiotic characteristics of aqueous-solid phase interfaces strongly influence chemical/biochemical reactions in the interface microenvironment of aqueous-solid phases. These reactions at interfaces are controlled mainly by biotic activity. Specifically, all aqueous-solid phase microenvironments contain living microorganisms that mediate biochemical transformations. Solid phases (e.g., soil and sediment particles) usually contain billions of microorganisms, with the aqueous phase containing smaller, but still significant, populations [22,33-39]. 

A new dimension in the development of nucleic acid based catalysts was introduced by Breaker and Joyce in 1994 when they isolated the first deoxyribozyme [111]. It is not unexpected that DNA is also able to catalyze chemical reactions because it was shown previously that ssDNA aptamers which bind to a variety of ligands can be isolated by in vitro selection [141]. In the meantime, several deoxyribozymes have been described which expand the range of chemical transformations accelerated by nucleic acid catalysts even further and raising question whether even catalytic DNA might have played some role in the pre-biotic evolution of hfe on earth [69-71]. 

Comparison of reaction mechanisms and products of transformation of catechol by biotic (tyrosinase) and abiotic (birnessite) catalysts... 

Figure 2.20. Transformation of catechol by laccase (0.4 units mT1), tyrosinase (0.4 units ml-1) and birnessite (600ugml 1) after repeated addition of substrate. Reprinted from Pal, S., Bollag, J.-M., and Huang, P. M. (1994). Role of abiotic and biotic catalysts in the transformation of phenolic compounds through oxidative coupling reactions. Soil Biol. Biochem. 26, 813-820, with permission from Elsevier.

We have chosen to follow Watts [24] and discuss chemical and biological transformation processes in the same section. Watts notes that, although this approach is somewhat nontraditional, it is advantageous in that understanding of the abiotic chemical reactions serves as a conceptual basis for understanding the biochemical reactions (which are essentially the same except for the fact that the biochemical reactions are mediated by microorganisms). Where a reaction is predominantly abiotic or biotic, it will be noted in the discussion. In this section, the fundamentals of each chemical or biological reaction will be discussed, and model formulations for the reaction kinetics presented. 

McCormick M. L., Bouwer E. J., and Adriaens P. (2002a) Carbon tetrachloride transformation in a dehned iron-reducing culture relative kinetics of biotic and abiotic reactions. Environ. Sci. Technol. 36, 403-410. 

Biotransformation refers to the process by which lipophilic (fat-soluble), xenobiotic (foreign), or endo-biotic (endogenous) chemicals are converted in the body by enzymatic reactions to products that are more hydrophilic (water-soluble). In this context, metabolism and metabolic transformation are synonymous with biotransformation. A xenobiotic is a relatively small (molecular weight <1000), nonnutrient chemical that is foreign to the species where metabolism occurs. 

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