Cometabolic transformations

Safinowski M, C Griebler, RU Meckenstock (2006) Anaerobic cometabolic transformation of polycyclic and heterocyclic aromatic hydrocarbons evidence from laboratory and field studies. Environ Sci Technol 40 4165-4173. 

Drzyzga O, A Schmidt, K-H Blotevogel (1996) Cometabolic transformation and cleavage of nitrodiphenylamines by three newly isolated sulfate-reducing bacterial strains. Appl Environ Microbiol 62 1710-1716. 

Higher-molecular-weight PAHs, such as pyrene, benzo(a)pyrene, and benzo(e)-pyrene, exhibit a high resistance to biodegradation. PAHs with three or more condensed rings tend not to act as a sole substrate for microbial growth and require cometabolic transformations. Neilson and Allard (1998) report a cometabolic reaction of pyrene, 1,2-benzanthracene, 3,4-benzopyrene, and phenanthrene in the presence of either naphthalene or phenanthrene. However, the cometabolic reactions are very slow in natural ecosystems. 

The BAT system operates based on principles of aerobic cometabolism. In cometabohsm, enzymes that the microbes produce in the process of consuming one particular compound (e.g., phenol) have the collateral effect of transforming another compound that normally resists biodegradation (e.g., chlorinated ethenes, especially lesser chlorinated ethenes such as dichloroethene or vinyl chloride). The BAT system operates under these principles by sorbing the chlorinated compounds from a vapor stream onto powdered activated carbon (PAC) where they are cometabolically transformed into a combination of end products, including new biomass, carbon dioxide, inorganic salts, and various acids. 

Incomplete aerobic transformations may involve cometabolic transformations and reactions resulting in recalcitrant dead-end metabolites. Cometabolic o-hydroxylation of MCPs and DCPs by a phenol monooxygenase has been shown, for example, in a Pseudomonas sp. (Knackmuss Hellwig, 1978) and by the toluene dioxygenase reaction in Pseudomonas putida (Spain Gibson, 1988 Spain et al., 1989)- Cometabolic transformation of CPs is also possible in aerobic mixed culture systems. Phenol- and toluene-enriched cultures completely removed 2,4-DCP, and the toluene enrichment also removed 2,4,6-TCP and PCP (Ryding et al., 1994). This PCP attack by the toluene enrichment involved an o-hydroxylation. 

Semprini L,McCarty PL (1992) Comparison between model simulations and field results for in-situ biorestoration of chlorinated aliphatics. Part 2. Cometabolic transformations. Ground Water 30 37-44... 

Adriaens P, Grbic-Galioc D. 1994. Cometabolic transformation of mono- and dichlorobiphenyls and chlorohydroxybiphenyls by methanotrophic groundwater isolates. Environ Sci Technol 28 1325-1330. 

Li, Y. and Loh, K. -C. 2007a. Hybrid-Hollow-Fiber Membrane Bioreactor for Cometabolic Transformation of 4-Chlorophenol in the Presence of Phenol. Journal of Environmental Engineering, 133,404-410. 

Incomplete reduction of a nitro group yielding a hydroxylaminoaromatic compound and the rearrangement of the latter into an aminophenol was first described in the yeast Rhodosporidium sp. as part of cometabolic transformation of 4-chloronitrobenzene (4). Characteristically, reductive pathways have been postulated for the mineralization of a number of nitroaromatics (de Bont, this volume). In many cases, however, aminoaromatic structures could not be identified as intermediates. Therefore, the above novel catabolic pathway with a hydroxylaminoaromatic compound as a key metabolite could be of more general importance in aerobic mineralization of nitroaromatic compounds. 

For those pesticides that are cometabolized, ie, not utilized as a growth substrate, the assumption of first-order kinetics is appropriate. The more accurate kinetic expression is actually pseudo-first-order kinetics, where the rate is dependent on both the pesticide concentration and the numbers of pesticide-degrading microorganisms. However, because of the difficulties in enumerating pesticide-transforming microorganisms, first-order rate constants, or half-hves, are typically reported. Based on kinetic constants, it is possible to rank the relative persistence of pesticides. Pesticides with half-hves of <10 days are considered to be relatively nonpersistent pesticides with half-hves of >100 days are considered to be relatively persistent. 

Alvarez-Cohen L, McCarty PL. 1991b. Product toxicity and cometabolic competitive inhibition modeling of chloroform and trichloroethylene transformation by methanotrophic resting cells. Appl Environ Microbiol 57 1031-1037. 

Kohler, H.-P. E., D. Kohler-Staub, and D. D. Focht, Cometabolism of polychlorinated biphenyls, enhanced transformation of Arochlor 1254 by growing cells , Appl. Environ. Microbiol., 54, 1940-1945 (1988). 

Kohler, H-P. E., Kohler-Staub, D. Focht,D.D. (1988a). Cometabolism of polychlorinated biphenyls enhanced transformation of Aroclor 1254 by growing bacterial cells. Applied and Environmental Microbiology, 54, 1940-5. 

A chemical subject to cometabolism. .. is transformed slowly, and the rate of conversion does not increase with time [low starting population in soils and water and no growth]. 

Weber and Adams (1995) observed the rapid reduction of the azo dye Disperse Blue 79 chemically as well as in three anoxic sediment/ water systems. Half lives were on the order of minutes to hours. An initial rapid loss of the dye was followed by a much slower rate of transformation, and, most probably, chemical or cometabolic processes were responsible for transformation. 

There are cases when a substrate is not used for growth, but is metabolized in the presence of a second substrate that is used to support microorganism reproduction. This type of transformation is called cometabolism. Cometabolic conversions that apparently involve a single enzyme include hydroxylations, oxidations, denitrations, deaminations, hydrolyses, acylations, and cleavages of ether bonds. Many of these conversions are complex and involve several enzymes. This may be explained by the existence of enzymes that perform a single type of reaction, but which act on a series of closely related molecules. 

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