Microbially mediated reactions

Several factors govern the transport and fate of hydrophobic organic chemicals in sediment/water environments microbially mediated reactions and sorption are major processes affecting the fate of these compounds in aquatic systems [166,366-368]. Aryl halides have been shown to undergo microbially-mediated dehalogenation under anaerobic conditions [38, 52, 68, 105, 116,... 

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. 

The fifth paper, "A Separative Bioreactor Direct Product Capture and pH Control," presented by Seth Snyder of the Argonne National Laboratory, reviewed development and performance of a novel bioreactor incorporating electrodeionization to simultaneously produce and separate products from both enzymatic and microbially mediated reactions. The sixth paper, " Optimization of Xylose Fermentation in Spent Sulfite Liquor by Saccharomyces cerevisiae 259ST," presented by Steven Helle of the University of British Columbia, provided an overview of an approach to fermentation optimization utilized to identify key process variables limiting use of the SSL for commercial ethanol production. 

Because Mn " " reacts rapidly with O2, reaction (21) may be restricted to anoxic zones in manganese-rich sediments. Although this reaction is similar to a microbially mediated reaction involving Fe(II) (reaction (26)), there is no evidence at present to suggest it is performed biotically. Luther et al. (1997) proposed a mechanism for producing N2 from NH4 that should be favored in aerobic zones where Mn02 is rapidly regenerated from Mn ... 

This reaction occurs abiotically. But it has been shown that Fe(III) can act as an electron acceptor in microbially mediated reactions (Lovely et al., 1994). 

The oxidation of organic matter proceeds by a number of microbially mediated reactions once free oxygen has been used up (see Section 5.5 Table 4.7). Although small amounts of nitrate (NOj), manganese (Mn) and iron (Fe) are... 

Additional information on microbial mediated reactions for a host of xenobiotics can be found at http //umbbd.ahc.umn.edu. The database contains information on some of the key degradation pathways associated with bioremediation. 

Crop fertilization can also produce substantial soil acidity. Continued use of ammonia fertilizers can lead to acidic soil conditions by the microbially mediated reaction... 

Fungi, which are active in upland environments, cease to exist in wetland soils. This is primarily due to the absence of oxygen and alteration in soil pH (acid to neutral) under anaerobic conditions. Overall, microbial biomass decreases under saturated soil conditions. The metabolic activities of anaerobic bacteria depend on alternate electron acceptors, such as oxidized forms of nitrogen, iron, manganese, and sulfur. Under wetland soil conditions, rates of many microbially mediated reactions decline, and some reactions may be eliminated and replaced by new ones. New microbial reactions are involved in the reduction of oxidized compounds during respiratory processes, resulting in the production of reduced compounds. 

The first section deals specifically with the spectroscopic/ microscopic tools that can be used in concert with macroscopic techniques. The second section emphasizes computer models that are used to elucidate surface mediated reaction mechanisms. The remainder of the volume is organized around reaction type. Sections are included on sorption/desorption of inorganic species sorption/desorption of organic species precipitation/dissolution processes heterogeneous electron transfer reactions photochemically driven reactions and microbially mediated reactions. What follows are a few highlights taken from the work presented in this volume. 

A second important microbially mediated reaction is the opposite of photosynthesis in which biomass is oxidized biochemically by elemental oxygen, converting the carbon in biomass to carbon dioxide ... 

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