Microbial metabolism reductive

Vorbeck C, H Lenke, P Fischer, JC Spain, H-J Knackmuss (1998) Initial reductive reactions in aerobic microbial metabolism of 2,4,6-trinitrotoluene. Appl Environ Microbiol 64 246-252. 

In summary, two general pathways are now accepted as the reaction basis of pyridine degradation by bacteria. One involves (i) hydroxylation reactions, followed by reduction, e.g., on Bacillus strain 4 and the other (ii) (aerobic) reductive pathway(s) not initiated by hydroxylations, e.g., on Nocardia strain Zl [348], Two review articles, one by Kaiser [320] and the other by Fetzner [326] gave the complete microbial metabolic pathways for several nitrogen compounds carried out in the presence of a variety of microorganisms, some of them previously studied by Professor Lingens [349], The complete degradation pathways of pyridine are shown in Fig. 29. 

Redox mediators, such as flavins or quinones, are usually involved in the azo bond reduction. Therefore, the azo bond cleavage is a chemical, unspecific reaction that can occur inside or outside the cell, relying on the redox potential of the redox mediators and of the azo compounds. Also the reduction of the redox mediators can be both a chemical and an enzymatic process. As a consequence, it is an evidence that environmental conditions can affect the azo dyes degradation process extent both directly, depending on the reductive or oxidative status of the environment, and indirectly, influencing the microbial metabolism. 

Fig. 22.7. Thermodynamic driving forces for various anaerobic (top) and aerobic (bottom) microbial metabolisms during mixing of a subsea hydrothermal fluid with seawater, as a function of temperature. Since the driving force is the negative free energy change of reaction, metabolisms with positive drives are favored thermodynamically those with negative drives cannot proceed. The drive for sulfide oxidation is the mirror image of that for hydrogentrophic sulfate reduction, since in the calculation 02(aq) and H2(aq) are in equilibrium.

The nature of the radioactivity in the water, soil and fish from the carbon-14 DDT experiment was examined by thin-layer chromatography as shown in Figure 5. The radioactivity in the water was very polar in nature and did not migrate appreciably from the origin. About 78% of the radioactivity in the soil was extracted with methanol. The major metabolite in the extractable fraction was DDD which represented 33% of the total radioactivity. The reductive dechlorination of DDT to DDD is a known pathway under anaerobic conditions and has been shown to be due to microbial metabolism (5). Since carbon-14 DDT was incor-... 

A few examples of chemoautolithotrophic processes have been mentioned in this chapter, namely anaerobic methane oxidation coupled to sulfate reduction and the ones listed in Table 12.2 involving manganese, iron, and nitrogen. Another example are the microbial metabolisms that rely on sulfide oxidation. Since sulfide oxidation is a source of electrons, it is a likely source of energy that could be driving denitrification, and manganese and iron reduction where organic matter is scarce. 

Kamnev AA (1998) Reductive Solubilization of Fe(lII) by Certain Products of Plant and Microbial Metabolism as a Possible Alternative to Siderophore Secretion. Dokl Biophys 358-360, 48 (translation from Dokl Akad Nauk 359 691). 

Some metals such as iron are reduced or oxidized by specific enzymes of microorganisms. Microbial metabolism generates products such as hydrogen, oxygen, H2O2, and reduced or oxidized iron that can be used for oxidation/reduction of metals. Reduction or oxidation of metals is usually accompanied by metal solubilization or precipitation. 

Although 2-phenylethanol can be synthesised by normal microbial metabolism, the final concentrations in the culture broth of selected microorganisms generally remain very low [110, 111] therefore, de novo synthesis cannot be a strategy for an economically viable bioprocesses. Nevertheless, the microbial production of 2-phenylethanol can be greatly increased by adding the amino acid L-phenylalanine to the medium. The commonly accepted route from l-phenylalanine to 2-phenylethanol in yeasts is by transamination of the amino acid to phenylpyruvate, decarboxylation to phenylacetaldehyde and reduction to the alcohol, first described by Ehrlich [112] and named after him (Scheme 23.8). 

Stone, A. T. (1987a). Microbial metabolates and the reductive dissolution of manganese oxides Oxalate and pyruvate. Geochim. Cosmochim. Acta 51, 919-925. 

Microbial metabolic activity in general is known both to accelerate transitions to stable equilibria and to produce metastable intermediate dissolved species and mineral precipitates that otherwise would not exist or would not be abundant. In general, most metabolic schemes that intervene in the existence and abundance of one anionic species or complex will do so with others, too, and this also has a big effect on the evaporitic and freezing chemistry dealt with by FREZCHEM. For example, dolomite formation is linked to sulfate reduction in one biogeochemical scheme. Lacking microbial activity,... 

This reaction is also catalyzed by superoxide dismutase (SOD), which occurs in milk at very low concentrations (Fox and Morrissey, 1981). Hydrogen peroxide can also be formed in milk as a result of microbial metabolism or by reduction of superoxide by ascorbic acid. A mean level of 0.02 mg/1 hydrogen peroxide has been reported in milk (Toyoda et al, 1982). 

Non-enzymatic attack In non-enzymatic attack of minerals by microbes, reactive products of microbial metabolism come into play. The microbial enzymes responsible for metabolic product formation are located below the cell envelope, in the cytoplasm of prokaryotes (Bacteria and Archaea) and in cell organelles and/or the cytoplasm of eukaryotes (e.g. fungi, algae, lichens). In these instances of microbial attack, physical contact of the microbial cells with the surface of a mineral being attacked is not essential. The reactive metabolic products are formed intracellularly and are then excreted into the bulk phase where they are able to interact chemically, i.e. non-enzymatically, with a susceptible mineral. Depending on the type of metabolic product and mineral, the interaction with the mineral may result in mineral dissolution or mineral diagenesis by oxidation or reduction or acid or base attack. Mineral dissolution or diagenesis may also be the result of complexation by a microbial metabolic product with that capacity. In some instances mineral attack may involve a combination of some of these reactions. 

Iron and manganese oxides are the most abundant components of Earth s surface that can serve as anaerobic terminal electron acceptors in microbial metabolism, yet it was recognized only recently that microorganisms play a key role their cycling. Despite early reports that suggested biological Fe(III) reduction was important in wet... 

Takai Y., Koyama T., and Kamura T. (1963a) Microbial metabolism in reduction process of paddy soils (Part 2). Soil Sci. Plant Nutr. (Tokyo) 9, 176—185. 

Table II summarizes the results for degradation of the CP isomers in East River cultures under sulfate-reducing conditions based on the stoichiometry in equation 11. Sulfate loss in the background controls were subtracted from the cultures to which CPs were added. As noted in Table II, the measured sulfate depletion corresponded to that calculated and provided evidence that CP metabolism was coupled to sulfate reduction. In these studies sulfate reduction is supported by two additional experimental observations. First, molybdate, which is a specific inhibitor of microbial sulfate reduction, was documented to stop the CP degradation. Active controls that did not receive molybdate continued to degrade CP. Second, radiolabeled 35S042 formed 35 S2 in active cultures and not in control cultures (33).

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