Phenolics microbial metabolism

Soil microorganisms produce many compounds that are potentially toxic to higher plants. Examples include members of the following antibiotics (1-6), fatty and phenolic acids (7-12), amino compounds (13-15), and trichothecenes (16, 17). "Soil sickness" and "replant problems" have been reported where certain crops or their residues interfere with establishment of a subsequent crop (18, 19). Toxins resulting from microbial activity sometimes are involved, but it is often unclear whether these are synthesized de novo in microbial metabolism or are breakdown products of the litter itself (20). 

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. 

Tabak HH, Chambers CW, Kabler PW. 1964. Microbial metabolism of aromatic compounds. I. Decomposition of phenolic compounds and aromatic hydrocarbons by phenol-adapted bacteria. J Bacteriol 87 910- 919. 

FIGURE 6.1 Illustration of the effects of mammalian metabolism and microbial metabolism on the redox potential of (poly)phenols found in plasma compared with their precursors in the diet and the aglycones commonly used in studies in vitro. (Reprinted from Clifford, M.N., Planta Med., 12, 1103, 2004. With permission.)... 

Phelps C. D. and Young L. Y. (1997) Microbial metabolism of the plant phenolic compounds femUc and syringic acids under three anaerobic conditions. Microbial. Ecol. 33, 206 - 215. 

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. 

Monagas M, Khan N, Andres-Lacueva C, et al. Dihydroxylated phenolic acids derived from microbial metabolism reduce lipopolysaccharide-stimulated cytokine secretion by human peripheral blood mononuclear cells. Br Nutr. 2009 102(2) 201 —206. 

Complete solution changes for multiple phenolic acid treatments were used because phenolic acids supplied to seedlings in the nutrient culture system disappeared from the nutrient solution within 24-48 h (Blum and Dalton 1985 Blum and Gerig 2005). This was due to microbial metabolism, physical breakdown, and/or root uptake. Since we did not want to confound nutrient and phenolic acid effects, complete solution changes were made. An additional benefit of this approach was to reset phenolic acid concentrations to the initial treatment levels for each solution change. This was important since recovery of seedling processes occurred rapidly after phenolic acid depletion (Blum and Dalton 1985 Blum and Rebbeck 1989 Blum and Gerig 2005). 

Multiple additions of phenolic acids were used because phenolic acid concentrations in soil decline rapidly after each addition of phenolic acids (Blum et al. 1987 Blum and Gerig 2006). This was due to microbial metabolism, physical breakdown, root uptake, and/or soil particle sorption. Recovery of seedling processes, although considerably slower than in nutrient culture, also occurred in seedling-soil systems (Blum et al. 1987 Blum and Gerig 2006). To maintain inhibition for extended time periods multiple additions of phenolic acids were required. 

The number of papers published in the field of nutritional metabo-lomics has increased rapidly over the past few years. While a detailed literature review of all papers is beyond the scope of this chapter, a more focused overview of some of the studies using functional ingredients will be presented. There are a number of studies which have investigated the effects of pol henols on metabolic effects in humans. Grun and colleagues developed a GC-MS metabolomis method to profile phenolic microbial fermentation products (Gmn et al. 2008). They successfully applied this in a cross-over human intervention trial where... 

Moussa C et al. (1997) Microbial models of mammalian metabolism. Fungal metabolism of phenolic and nonphenolic p-cymene-related drugs and prodrugs. 11. Metabolites of nonphenolic derivatives. Drug Metab Dispos 25(3) 311-316... 

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