Microbial degradation of phenol

Bekins et al. (1998) followed the concentration of phenol, CeHsCfifraq), in a laboratory experiment as it was degraded over time within a microcosm containing a consortium of methanogens. The degradation can be represented by a reaction, 

The experiment contained sufficient nutrients and phenol was present at sufficiently low levels, about 40 mg kg-1 initially, that the substrate was the rate-limiting reactant. Methanogenic consortia are slow growing when observed on the time scale of the experiment, which lasted about 40 days. The biomass concentration, in fact, was not observed to change significantly. The reaction, furthermore, remained far from equilibrium, so the reverse reaction rate was negligible, compared to the forward reaction. 

We can, therefore, reasonably expect the degradation to behave as an enzymatically catalyzed reaction in which phenol is the substrate and the microbial consortium serves as the enzyme. As discussed in Chapter 17, reaction rate in this case can be represented as, 

Since the enzyme concentration was not observed separately from the rate constant, we carry the product k+ m. in this equation as rmax, the maximum reaction rate. Bekins el al. (1998) fitted their results using values of 1.4 mg kg-1 day-1 (or 1.7 x 10-10 molal s-1) for rmax, and 1.7 mg kg-1 (1.8 x 10-5 molal) for Ka, the half-saturation constant. In a field application lasting many years, of course, the assumption that enzyme concentration remains constant might not be valid, 

The default thermodynamic dataset does not contain an entry for phenol, so to trace the reaction we need to add the reaction, 

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Flyvbjerg J, Arvin E, Jensen BK, et al. 1993. Microbial degradation of phenols and aromatic hydrocarbons in creosote-contaminated groundwater under nitrate-reducing conditions. J Contain Hydrol... 

More recent laboratory studies from Niqui-Arroyo et al. (2006) and Niqui-Arroyo and Ortega-Calvo (2007) demonstrated an up to 10-fold increase of PAH degradation in experiments with applied electric field compared with control experiments without electric current. Additionally, they showed that a periodic change of electrode polarity resulted in a more stable and better degradation efficiency. Also Luo et al. (2005) observed a stimulated microbial degradation of phenol in the presence of an electric field. In their experiments, bioremediation rates could be increased... 

Juang, R. S. and Wu, C. Y. 2007. Microbial degradation of phenol in high-salinity solutions in suspensions and hollow fiber membrane contactors. Chemosphere, 66,191-198. 

Shivaraman N, Kumaran P, Pandey RA, et al. 1985. Microbial degradation of thiocyanate, phenol and cyanide in a completely mixed aeration system. Environ Pollut, Ser A 39 141-150. 

Healy and Young (58) observed that the conversion of vanillic and ferulic acids under anaerobic conditions to methane and CO2 was nearly stoichiometric. More than half of the organic carbon could potentially be converted to methane. This could have great importance in studies where the degradation of phenolic compounds are studied by trapping the evolved CO2. Under anaerobic conditions, part of the normal CO2 evolution may be shifted to methane production with a subsequent low reporting of CO2 evolved, and an underestimation of microbial activity in the soil (51). 

Microbial degradation of biocides has been described by Hugo [72] who points out that soil organisms are able to break down substances such as phenols added as fumigants. He also reviewed the utilization by bacteria of aromatic compounds (including the preservatives cresol, phenol, benzoic acid and esters of 4-hydroxybenzoic acid). Several types of preservatives and disinfectants, such as the QACs (e.g. cetrimide, cetylpyridinium chloride, benzalkonium chloride), chlorhexidine and phenylethanol can also be inactivated. Significantly, this only occurs at concentrations well below inhibitory or in-use concentrations [33] and thus cannot be responsible for insusceptibility. A further comment about chlorhexidine is given below. 

Eield, J. A. and Sierra-Alvarez, R. 2008. Microbial degradation of chlorinated phenols. Reviews in Environmental Science and Biotechnology, 7 211 1. 

Steiert, J.G. and R.L. Crawford. 1985. Microbial degradation of chlorinated phenols. Trends Biotechnol. 3 300-305. 

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. 

A similar relationship was also found in the microbial degradation of various halogenated phenols (Alexander and Lustigman, 1966). Further investigation of such structural correlations may create good possibilities for the preparation of biodegradable pesticides of shorter life. 

Sih, Wang, and their collaborators elucidated the pathway whereby 5 is transformed into 8 via 6 and 7. A key reaction is the 4-hydroxylation of the phenolic intermediate 5. Sih has recently shown that the same process is also implicated in the microbial degradation of estrone by a particular Nocardia sp. (Ap-13), which is illustrated here. Intermediate B corresponds to 6 and C to 7. The probable structure of... 

Vanillin is a phenolic aldehyde used in the food industry as a flavoring agent, mainly applied in ice cream and chocolate industries, with smaller amounts being used in confectionary and baked goods. Vanillin and related phenols can also be produced by microbial degradation of lignin. 

During fermentation, the betacyanins turned out to be more stable than the betaxanthins, which is assumed to be due to their thermal stability rather than different tendencies of pigments toward microbial degradation. Besides these biological tools, beet extracts may also be purified by column chromatographic techniques. After removal of sugars, salts, and phenolics, the nature-derived color preparation will, however, require E number labeling. ... 

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. 

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