Co-metabolism

Dalton H, DI Stirling (1982) Co-metabolism. Phil Trans Roy Soc London B 297 481-496. 

Horvath RS (1972) Microbial co-metabolism and the degradation of organic compounds in nature. Bacteriol Rev 36 146-155. 

Horvath RS, P Flathman (1976) Co-metabolism of fluorobenzoates by natural microbial populations. Appl Environ Microbiol 31 889-891. 

Spokes JR, N Walker (1974) Chlorophenol and chlorobenzoic acid co-metabolism by different genera of soil hacteria. Arch Microbiol 96 125-134. 

In some cases, microorganisms can transform a contaminant, but they are not able to use this compound as a source of energy or carbon. This biotransformation is often called co-metabolism. In co-metabolism, the transformation of the compound is an incidental reaction catalyzed by enzymes, which are involved in the normal microbial metabolism.33 A well-known example of co-metabolism is the degradation of (TCE) by methanotrophic bacteria, a group of bacteria that use methane as their source of carbon and energy. When metabolizing methane, methanotrophs produce the enzyme methane monooxygenase, which catalyzes the oxidation of TCE and other chlorinated aliphatics under aerobic conditions.34 In addition to methane, toluene and phenol have been used as primary substrates to stimulate the aerobic co-metabolism of chlorinated solvents. 

Tetrachoroethylene (perchloroethylene, PCE) is the only chlorinated ethene that resists aerobic biodegradation. This compound can be dechlorinated to less- or nonchlorinated ethenes only under anaerobic conditions. This process, known as reductive dehalogenation, was initially thought to be a co-metabolic activity. Recently, however, it was shown that some bacteria species can use PCE as terminal electron acceptor in their basic metabolism i.e., they couple their growth with the reductive dechlorination of PCE.35 Reductive dehalogenation is a promising method for the remediation of PCE-contaminated sites, provided that the process is well controlled to prevent the buildup of even more toxic intermediates, such as the vinyl chloride, a proven carcinogen. 

The primary metabolism of an organic compound uses a substrate as a source of carbon and energy. For the microorganism, this substrate serves as an electron donor, which results in the growth of the microbial cell. The application of co-metabolism for bioremediation of a xenobiotic is necessary because the compound cannot serve as a source of carbon and energy due to the nature of the molecular structure, which does not induce the required catabolic enzymes. Co-metabolism has been defined as the metabolism of a compound that does not serve as a source of carbon and energy or as an essential nutrient, and can be achieved only in the presence of a primary (enzyme-inducing) substrate. 

Fortuitous or co-metabolic biodegradation may account for a significant portion of the removal of xenobiotics in the environment.24 Numerous examples of co-metabolic activity have been described for pure substrates,22 but co-metabolism has been very difficult to demonstrate in mixed-substrate, mixed-culture systems, because products of the co-metabolic reactions of one species may be degraded by another.24 To encourage co-metabolism, easily degradable co-substrates should be included in the leachate prior to biological treatment. Fatty acids, which often occur in landfill leachates, may fulfill this requirement. 

Venkataramani, E.S. and Ahlert, R.C., Role of co-metabolism in biological oxidation of synthetic compounds, Biotechnol. Bioeng., 27, 1306-1311, 1985. 

The capacity of WRF to transform and mineralize a wide range of pollutants without a preconditioning period via co-metabolic pathways makes them interesting for the degradation of recalcitrant xenobiotics. The use of WRF and their LMEs for the removal of xenobiotics has been reviewed elsewhere [1-7]. 

The pollutant degradation by WRF is a co-metabolic process in which additional C and N sources are required. This capacity represents an advantage respect bacteria as it prevents the need to internalize the pollutant, thus avoiding toxicity problems and permitting to attack low-soluble compounds. 

Pre-Inoculation Steps Determination and optimization of an adaptive co-metabolic and symbiotic bio-products system to achieve both, hemicycle A (carboxylation/oxidative stage) and hemicycle B (decarboxylation/reductive stage), and of the sequence and timing of events in terms of bio-products inoculation to accomplish the RACDC. 

Two processes of microbial degradation must be emphasized in our understanding the fate of chemicals in the environment, metabolism via mineralization or co-metabolism. The former is specifically for process carried by bacterial and support the growth of the microorganisms while the latter one involves the presence of a second source of carbon and energy in which the microorganisms actually use these for growth, but also... 

Strubel, V., Rast, H. G., Fietz, W., Knackmuss, H. J. and Engesser, K. H. (1989). Enrichment of dibenzofuran utilizing bacteria with co-metabolic potential toward dibenzodioxin and other anellated aromatics, FEMS Microbiol. Lett., 58, 233-238. 

The following section discusses the different types and phases of microbial degradation of organic pollutants present at aqueous-solid phase interfaces. This includes a discussion of growth-linked biodegradation, acclimation, detoxification, activation, defusing, threshold, and co-metabolism. 

The transformation of an organic compound by a microorganism that is unable to use the substrate or one of its constituent elements as a source of energy is termed co-metabolism. The active microbial populations thus derive no nutritional benefit from the substrates they co-metabolize. The energy sufficient to sustain growth fully is not acquired even if the conversion is an oxidation and releases energy, and the C, N, S, or P that may be in the molecule is not used as a source of these elements for biosynthetic purposes [93-95,185,188-190,202]. 

In co-metabolism, a partial oxidation of the substrate occurs, but the energy derived from the oxidation is not used to support growth of new microbial cells [96-98]. This phenomenon arises when microorganisms possess enzymes that... 

Halogenated aliphatics can be partially or completely degraded under anaerobic conditions through a transformation reaction called reductive de-halogenation. Often a co-metabolic degradation step, reductive dehalogenation... 

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