| Description: |
A large part of the emitted methane is produced by methanogenic archaea and released through the gas vascular system of the rice plant. Rice Cluster I (RC-I) methanogens in the rice rhizosphere were found to play the key role in methane production from plant-derived carbon. They were identified as the predominant methanogens in rice paddy soils of geographically diverse regions. Several attempts have been made to isolate RC-I representatives in pure culture. Althoug isolation failed, one of these attempts with rice paddy soil as the inoculum resulted in the methanogenic consortium MRE50, in which RC-I methanogens constituted the only archaeal components. The complete genome sequence of a single RC-I representative was unambiguously reconstructed. The genome of the Uncultured methanogenic archaeon RC-I is made up of a single circular chromosome of 3,179,916 base pairs with 3103 coding sequences. The central energy metabolism of RC-I is H2/CO2-dependent methanogenesis. It can use formate and formaldehyde for methanogenic growth. It encodes only an incomplete methanol-coenzyme M methyltransferase system. It appears to use the Embden-Meyerhof-Parnas pathway for carbohydrate metabolism, thus involving bacterial-type enzymes not yet identified in archaea. The biosynthetic pathways for all amino acids except glutamate appear to be complete. Two mechanisms for nitrogen acquisition exist besides glutamate uptake: ammonium assimilation (glutamine synthetase, glutamate sythase and glutamate dehydrogenase) and dinitrogen fixation (nitrogenase). Sulfur assimilation is predicted to occur thanks to the reduction of sulfate to sulfide. |
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