Metabolism under methanogenic conditions

Figure 3. Metabolism of 2,6-dichlorophenol under methanogenic conditions. Duplicate cultures were established under methanogenic conditions with pond water. Re-addition of substrate is indicated by the arrow. (Adapted from 38).

The metabolic fate of RDX was studied in a mixed culture incubated under methanogenic conditions. Analysis by HPLC confirmed the loss of RDX and the formation of mono-, di-, and trinitroso-RDX as transient biodegradation intermediates. An additional peak observed in the HPLC chromatogram was identified by LC-MS as hydroxylamino-dinitroso-l,3,5-triazine <2001ETC1874>. 

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. 

The most fundamental difference between aerobic and anaerobic metabolism is energy yield. Oxidation of glucose yields —2,900 kJ moP under aerobic conditions (Equation (1)) compared to —400kJmol under typical methanogenic conditions (Equation (2)) ... 

Another environmental parameter that is important to methane emissions is soil temperatnre. Soil temperature affects the metabolic activity of microorganisms that prodnce substrates for inhibitors of methanogenesis as well as the methanogens themselves. Temperatnre is directly related to methanogenesis under field conditions (Schutz et al., 1990 Westermann, 1993). Methane emission rates generally parallel soil temperature levels. 

Conrad R, Schink B, Phelps TJ. 1986. Thermodynamics of Ha-producing and Ha-consuming metabolic reactions in diverse methanogenic environments under in-situ conditions. FEMS Microbiology Ecology 38 353-360. 

Carbamates such as Aldicarb undergo degradation under both aerobic and anaerobic conditions. Indeed the oxidation of the sulfur moiety to the sulfoxide and sulfone is part of the activation of the compound to its most potent form. Subsequent aerobic metabolism can completely mineralize the compound, although this process is usually relatively slow so that it is an effective insecticide, acaricide and nematocide. Anaerobically these compounds are hydrolyzed, and then mineralized by methanogens (61). 

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