| Methanocella paludicola gen. nov., sp. nov., a methane-producing archaeon, the first isolate of the lineage 'Rice Cluster I', and proposal of the new archaeal order Methanocellales ord. nov.
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Sakai S.,Imachi H.,Hanada S.,Ohashi A.,Harada H.,Kamagata Y.
Int. J. Syst. Evol. Microbiol. 58 (2008) 929-36 [PMID: 18398197] Abstract
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| Abstract: A novel mesophilic, hydrogenotrophic methanogen, strain SANAET, was isolated from an anaerobic, propionate-degrading enrichment culture, which was originally established from rice paddy soil. The cells were non-motile, Gram-negative and rod-shaped (1.8-2.4 microm long by 0.3-0.6 microm wide). Growth of strain SANAET was observed at 25-40 degrees C, with an optimum temperature range for growth of 35-37 degrees C. The pH range for growth was 6.5-7.8, with an optimum at pH 7.0. The salinity range for growth was 0-1 g NaCl l(-1) (0-17 mM). The isolate was able to utilize H2/CO2 and formate for growth and methane production. The G+C content of the genomic DNA was 56.6 mol%. Based on comparative 16S rRNA gene sequence analysis, strain SANAET was affiliated with a clone lineage of the Archaea, Rice Cluster I (RC-I), placing it between the orders Methanosarcinales and Methanomicrobiales within the class 'Methanomicrobia'. 16S rRNA gene sequence similarities between strain SANAET and members of Methanosarcinales were in the range 80.0-82.8 %, and those between the strain and members of Methanomicrobiales ranged from 77.5 to 82.4 %. In addition to 16S rRNA gene analysis, sequence analysis of the mcrA gene (encoding the alpha subunit of methyl-coenzyme M reductase, a key enzyme in the methane production pathway) also showed that strain SANAET was affiliated with the RC-I lineage. Here, we propose the name Methanocella paludicola gen. nov., sp. nov. for the isolate, the first of the RC-I lineage. The type strain is SANAET (=JCM 13418T=NBRC 101707T=DSM 17711T). In addition, we also propose the status of order for the RC-I lineage, for which we propose the name Methanocellales ord. nov. |
| Isolation of key methanogens for global methane emission from rice paddy fields: a novel isolate affiliated with the clone cluster rice cluster I.
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Sakai S.,Imachi H.,Sekiguchi Y.,Ohashi A.,Harada H.,Kamagata Y.
Appl. Environ. Microbiol. 73 (2007) 4326-31 [PMID: 17483259] Abstract
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| Abstract: Despite the fact that rice paddy fields (RPFs) are contributing 10 to 25% of global methane emissions, the organisms responsible for methane production in RPFs have remained uncultivated and thus uncharacterized. Here we report the isolation of a methanogen (strain SANAE) belonging to an abundant and ubiquitous group of methanogens called rice cluster I (RC-I) previously identified as an ecologically important microbial component via culture-independent analyses. To enrich the RC-I methanogens from rice paddy samples, we attempted to mimic the in situ conditions of RC-I on the basis of the idea that methanogens in such ecosystems should thrive by receiving low concentrations of substrate (H(2)) continuously provided by heterotrophic H(2)-producing bacteria. For this purpose, we developed a coculture method using an indirect substrate (propionate) in defined medium and a propionate-oxidizing, H(2)-producing syntroph, Syntrophobacter fumaroxidans, as the H(2) supplier. By doing so, we significantly enriched the RC-I methanogens and eventually obtained a methanogen within the RC-I group in pure culture. This is the first report on the isolation of a methanogen within RC-I. |
| Genome of Rice Cluster I archaea--the key methane producers in the rice rhizosphere.
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Erkel C.,Kube M.,Reinhardt R.,Liesack W.
Science 313 (2006) 370-2 [PMID: 16857943] Abstract
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| Abstract: Rice fields are a global source of the greenhouse gas methane, which is produced by methanogenic archaea, and by methanogens of Rice Cluster I (RC-I) in particular. RC-I methanogens are not yet available in pure culture, and the mechanistic reasons for their prevalence in rice fields are unknown. We reconstructed a complete RC-I genome (3.18 megabases) using a metagenomic approach. Sequence analysis demonstrated an aerotolerant, H2/CO2-dependent lifestyle and enzymatic capacities for carbohydrate metabolism and assimilatory sulfate reduction, hitherto unknown among methanogens. These capacities and a unique set of antioxidant enzymes and DNA repair mechanisms as well as oxygen-insensitive enzymes provide RC-I with a selective advantage over other methanogens in its habitats, thereby explaining the prevalence of RC-I methanogens in the rice rhizosphere. |
| Rice Cluster I methanogens, an important group of Archaea producing greenhouse gas in soil.
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Conrad R.,Erkel C.,Liesack W.
Curr. Opin. Biotechnol. 17 (2006) 262-7 [PMID: 16621512] Abstract
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| Abstract: Methane, which is an important greenhouse gas, is to a large part produced by methanogenic archaea in anoxic soils and sediments. Rice Cluster I methanogens have been characterized on the basis of their 16S rRNA and mcrA gene sequences, and were found to form a separate lineage within the phylogenetic radiation of Methanosarcinales and Methanomicrobiales. As isolation has not been achieved until recently, our knowledge of distribution, physiology and environmental significance of Rice Cluster I is solely based on molecular biology techniques. Rice Cluster I seems to be widely distributed, particularly in rice fields, possibly occupying different niches among the methane producers. One niche seems to be methane production on roots driven by plant photosynthesis, contributing substantially to the release of methane from rice fields into the atmosphere. |
| Clime change 2001, the scientific basis.
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Dentener F, Derwent R, Dlugokencky E, Holland E, Isaksen I, Katima J, Kirchhoff V, Matson P, Midgley P and Wang M.
Third Assessment Report of the Intergovernmental Panel on Climate Change. (2001) |
