A novel mesophilic, hydrogenotrophic methanogen, strain SANAE, 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 μm long by 0.3–0.6 μm wide). Growth of strain SANAE was observed at 25–40 °C, with an optimum temperature range for growth of 35–37 °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 (0–17 mM). The isolate was able to utilize H/CO 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 SANAE was affiliated with a clone lineage of the , Rice Cluster I (RC-I), placing it between the orders and within the class ‘’. 16S rRNA gene sequence similarities between strain SANAE and members of were in the range 80.0–82.8 %, and those between the strain and members of ranged from 77.5 to 82.4 %. In addition to 16S rRNA gene analysis, sequence analysis of the gene (encoding the subunit of methyl-coenzyme M reductase, a key enzyme in the methane production pathway) also showed that strain SANAE was affiliated with the RC-I lineage. Here, we propose the name gen. nov., sp. nov. for the isolate, the first of the RC-I lineage. The type strain is SANAE (=JCM 13418=NBRC 101707=DSM 17711). In addition, we also propose the status of order for the RC-I lineage, for which we propose the name ord. nov.

Keyword(s): RC-I, Rice Cluster I

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