Oxidation-reduction reactions, microbial

The oxidation-reduction reactions of C, N, S, and O in soils are, virtually without exception, catalyzed by microbial enzymes. These reaction rates without such catalysis are very slow (irreversible). Even with catalysis, the reactions are quite irreversible. The behavior of carbon and nitrogen in particular is dominated by nonequilibrium. 

In the absence of oxygen, the complete remineralization of complex organic molecules to CO2 is a chemically difficult problem that cannot be accomplished by a single microbial metabolism. Instead, such substrates are degraded into successively smaller pieces via the activities of multiple groups of microorganisms ([19], Fig. 1). Most of these sequential steps are oxidation-reduction reactions... 

A major factor in the chemistry of the aquatic system shown in Figure 3.7 is the biochemical photosynthetic production of organic matter represented as CH2O. Organic matter is a biochemical reducing agent, and when it sinks into the hypolimnion it is oxidized by microorganism-mediated processes that, for example, reduce NO3 and 804 to NHJ and H2S, respectively. Two important microbially mediated oxidation-reduction reactions of CHjO are reaction with dissolved O2... 

Oxidation-reduction reactions can cause substantial errors in analysis. For example, soluble iron(II) and manganese(II) are oxidized to insoluble iron(III) and manganese(IV) compounds when an anaerobic water sample is exposed to atmospheric oxygen. Microbial activity can decrease phenol or biological ojg gen demand (BOD) values, change the nitrate-nitrite-ammonia balance, or alter the relative proportions of sulfate and sulfide. Iodide and cyanide frequently are oxidized. Chromium(VI) in solution may be reduced to insoluble chromium(III). Sodium, silicate, and boron are leached from glass container walls. 

Fig. 2. Oxidation and reduction reactions using microbial transformation for steroid synthesis.

Fuel cell applications Manganese dioxide as a new cathode catalyst in microbial fuel cells [118] OMS-2 catalysts in proton exchange membrane fuel cell applications [119] An improved cathode for alkaline fuel cells [120] Nanostructured manganese oxide as a cathodic catalyst for enhanced oxygen reduction in a microbial fuel cell [121] Carbon-supported tetragonal MnOOH catalysts for oxygen reduction reaction in alkaline media [122]... 

Francis (1990) has summarized the numerous possible microbially mediated reactions resulting in the mobilization or immobilization of metals and found that major interactions include oxidation-reduction processes, biosorption and immobilization by cell biomass and exudates, and mobilization by microbial metabolites. A profound issue in metal remediation is that through microbial action, metals can readily be re-mobilized, creating toxicity issues in sites where metals are not completely removed. 

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