Methanogens Subject

Methyl-substituted indole has been the subject of an investigation and the degradation metabolites were identified [346], An indole-degrading methanogenic consortium induced a two-step reaction on 3-methylindole, through a hydroxylation pathway that... 

Soil. In a methanogenic aquifer material, /ra/ 5-l, 2-dichloroethylene biodegraded to vinyl chloride (Wilson et al., 1986). Under anoxic conditions ra/ 5-l,2-dichloroethylene, when subjected to indigenous microbes in uncontaminated sediments, degraded to vinyl chloride (Barrio-Lage et al., 1986). tra/ 5-l,2-Dichloroethylene showed slow to moderate degradation concomitant with the rate of volatilization in a static-culture flask-screening test (settled domestic wastewater inoculum) conducted at 25 °C. At concentrations of 5 and 10 mg/L, percent losses after 4 wk of incubation were 95 and 93, respectively. The amount lost due to volatilization was 26 to 33% after 10 d (Tabak et al, 1981). 

Previous considerations of the pathways of hexose catabolism in archaebacteria have indicated that it is most sensible to consider them with respect to the phenotypes of the organisms, that is the extreme halophiles, the thermophiles and the methanogens[l,2]. This is the strategy to be adopted here, although it is reiterated that these groupings do not necessarily reflect genotypic relationships, a subject comprehensively covered in other chapters. 

Class III RNRs are oxygen-sensitive enzymes found in some facultative anaerobes [23-25]. The corresponding genes are not expressed under aerobic conditions. On the basis of sequence comparisons, it also seems likely that methanogens, such as Methanococcus jannaschii and Methanobacterium thermoautotrophicum use a class III enzyme for deoxyribonucleotide synthesis [26, 27]. The prototype of class III RNRs, the enzyme that P. Reichard at the Karolinska Institute (Sweden) and we discovered in 1987 in anaerobically growing E. coli cells [23], is the subject of this chapter. 

Recently, methanogens and their diversity have been the subject of increasing interests due to the methane production by ruminants (Firkins et al. 2008). Much research is still in progress to study methanogens in order to mitigate methane emission from ruminants. 

Our early work with dinoseb, a nitrophenolic herbicide commonly found as a soil contaminant, showed that under microaerophilic conditions, it is transformed to persistent multimeric forms that remain toxic, while under well-aerated conditions, no degradation occurs (29). However, in studies pre-dating our munitions work, we enriched an anaerobic consortium that fermented dinoseb and other nitroaromatic compounds under methanogenic conditions (16, 17). These initial observations ultimately led to our treatment of soils containing complex mixtures of TNT, dinitrotoluenes, mononitrotoluenes, nitrobenzoates, and related compounds (33), which showed that all contaminants could be removed to below detection limits of gas chromatography/mass-spectrometry. Even though biological treatment of several of these compounds in well-aerated cultures has been described, many of them are subject to polymerization reactions under microaerophilic conditions, which are almost certain to occur in soil treatment systems that are not maintained absolutely anoxic (18). 

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