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Methanogens play an important role in global climate because they are the largest natural sources of atmospheric methane - a heat-trapping greenhouse gas 21 times more potent than carbon dioxide. The methanogens and their relatives are phenotypically heterogenous comprising of extreme halophiles, sulphate reducing species (genus Archaeoglobus) and two types of thermopiles (the genus Thermoplasma and the Thermococcus - Pyrococcus group). The name proposed for this group of methanogens is Euryarchaeota. Methanogens have been isolated from faeces of rat, horse, pig, monkey, baboon, rhinoceros, hippopotamus, giant panda, goose, turkey and chicken. The chicken and turkey harbour species of Methanogenium. In sheep, Methanobrevibacter strains - SM9, M6 and NT7, Methanobrevibacter thaueri, Methanobrevibacter ruminantium, Methanobrevibacter acididurans, and Methanosphaera stadtmanae have been identified. In feedlot cattle, it was found that the methanogens had 89.8%-100% similarity to cultivated methanogens belonging to the orders Methanobacteriales, Methanomicrobiales, and Methanosarcinales, and some were 74.1%-75.8% similar to Thermoplasma volcanium and Thermoplasma acidophilum.
Methanogens play an important role in global climate because they are the largest natural sources of atmospheric methane - a heat-trapping greenhouse gas 21 times more potent than carbon dioxide. Phylogenetically, the Archaea fall into two distinct groups or in two major lineages (Woese, 1987 and Richter et al., 1988). The methanogens and their relatives are phenotypically heterogenous, comprising of extreme halophiles, sulphate reducing species (genus Archaeoglobus) and two types of thermophiles (the genus Thermoplasma and the Thermococcus - Pyrococcus group). The name proposed for this group of methanogens is Euryarchaeota. For this kingdom, the name commonly used is euryarchaeotes or more commonly euryotes. The other archaeal kingdom namely Crenarchaeota comprises thermo acidophiles, sulphur dependent archaea bacteria, eocytes or extreme thermophiles.
It is a relatively physiologically homogeneous group, whose niches are extremely thermophilic. Thermophilic nature is seen in both the major branches of archaea and this could be the ancestral phenotype of Archaea (Woese et al., 1990). Prior to the development of molecular-based methods, classical microbiological techniques were used to presumptively identify methanogens from the digestive tracts of animals (Miller and Wolin, 1986). With the growing use of molecular techniques to investigate complex microbial systems, the application of these methods has proven to be very effective for the characterization of microbial communities, especially methanogen diversity in the rumen (Lin et al., 1997; Tokura et al., 1999; Yanagita et al., 2000; Tajima et al., 2001a, 2001b; Irbis et al., 2004; Regensbogenova et al., 2004; Skillman et al., 2004; and Wright et al., 2004) and other diverse anaerobic environments (Godon et al., 1997; Huang et al., 2002; Utsumi et al., 2003; and Raul Snell-Castro et al., 2005). |
