Sulfate-reducing and methanogenic bacteria

Most studies in the microbial metabolism of nitroaromatic compounds used aerobic microorganisms. In most cases no mineralization of nitroaromatics occurs, and only superficial modifications of the structures are reported. However, under anaerobic sulfate-reducing conditions, the nitroaromatic compounds reportedly undergo a series of reductions with the formation of amino compounds. For example, trinitrotoluene under sulfate-reducing conditions is reduced to triaminotoluene by the enzyme nitrite reductase, which is commonly found in many Desulfovibrio spp. The removal of ammonia from triaminotoluene is achieved by reductive deamination catalyzed by the enzyme reductive deaminase, with the production of ammonia and toluene. Some sulfate reducers can metabolize toluene to (X) sub 2. Similar metabolic processes could be applied to other nitroaromatic compounds like nitrobenzene, nitrobenzoic acids, nitrophenols, and aniline. Many methanogenic bacteria can reduce nitroaromatic compounds to amino compounds. 

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Santegoeds C. M., Damgaard L. R., HesseUnk C., Zopfi J., Lens P., Muyzer G., and DeBeer D. (1999) Distribution of sulfate-reducing and methanogenic bacteria in anaerobic aggregates determined by microsensor and molecular analyses. Appl. Environ. Microbiol. 65, 4618—4629. 

Stams A. J. M. and Hansen T. A. (1984) Fermentation of glutamate and other compounds by Acidaminobacter hydrogenoformans gen. nov. sp. nov., an obhgate anaerobe isolated from black mud. Studies with pure cultures and mixed cultures with sulfate-reducing and methanogenic bacteria. Arch. Microbiol. 137, 329—337. 

Name types of organic molecules (substrates) that may be utilized by aerobic, facultative anaerobic (i.e., nitrate-, iron-, and manganese-reducing bacteria), and obligate anaerobic (sulfate-reducing and methanogenic bacteria) in wetland environments. 

Figure 3. Summary of DMS transformations. 1) aerobic and anaerobic bacteria 2) chemical and probably biochemical oxidation 3) aerobic and anaerobic bacteria 4) thiol S-methyltransferase S) sulfate reducers and methanogens 6) aerobic bacteria (hyphomicrobia and thiobacilli) 7) chemical and biochemical (aerobic and anaerobic) 8) chloroperoxidase 9) mechanism unknown 10) aerobic and anaerobic bacteria.

Microbial redox processes. Different metabolic types of bacteria (denitrifiers, manganese reducers, iron reducers, sulfate reducers, and methanogens) occur at landfill sites. Some of these metabolic types (sulfate reducers and methanogens) can be separated into physiological... 

In combination with Eh, pH strongly influences the types of bacteria that will be present. High- to medium-pH, low-Eh environments will generally restrict bacterial populations to sulfate reducers and heterotrophic anaerobes.187 In reducing conditions, pH strongly affects whether methanogenic or sulfate-reducing bacteria predominate.43... 

In Hg-resistant bacteria that are resistant to organic forms of Hg such as phenylmercuric acetate and methylmercury chloride, lyases are involved in the fission of the C-Hg to form Hg + and benzene or methane, and the enzyme has been partly purified (Schottel 1978). The Hg + may then be reduced to nontoxic Hg°. The situation under anaerobic conditions for sulfate-reducing bacteria is complicated by the possibility of both methylation and demethylation in the same strain (Pak and Bartha 1998), plausibly by operation of the acetyl-CoA pathway (Choi et al. 1994 Ekstrom et al. 2003). Under anaerobic conditions, demethylation, though not methylation, has been reported for a methanogen (Pak and Bartha 1998). 

At many sites, the subsurface environment will be anoxic or even anaerobic due to the activity of aerobic and facultatively anaerobic bacteria in the surface layers of the soil. It is therefore essential to take into consideration the extent to which anaerobic degradation may be expected to be significant. Reactions may take place under sulfidogenic or methanogenic conditions, and the occurrence of sulfate at sites containing building material waste and the metabolic versatility of sulfate-reducing bacteria makes them particularly attractive. 

Industrial wastewater containing precursors and synthesis products of 15 sulfonated azo dyes Anaerobic baffled reactor containing mixed sulfate reducing bacteria, and methanogens In an anaerobic baffled reactor, almost a complete removal of color was observed in the reactor within 100 days of operation [182]... 

Reactive Orange 96 Anaerobic culture of sulfate-reducing bacteria, methanogens, and fermentative bacteria Sulfate-reducing bacteria removed 95% of the dye in 40 h. Methane producing bacteria did not contribute in dye removal. Fermentative bacteria could remove only 30% of the dye in 90 h [186]... 

The two functional groups of microbes in the aquifer, the sulfate reducing bacteria and methanogens, are present initially in small amounts, just 10-6 mg kg-1, but their populations can grow as they derive energy by metabolizing the acetate. 

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