Aceticlastic and NaCl-Requiring Methanogen “Methanosaeta pelagica” sp. nov., Isolated from Marine Tidal Flat Sediment
ABSTRACTAmong methanogens, only 2 genera,MethanosaetaandMethanosarcina, are known to contribute to methanogenesis from acetate, andMethanosaetais a specialist that uses acetate specifically. However,Methanosaetastrains so far have mainly been isolated from anaerobic digesters, despite the fact that it is widespread, not only in anaerobic methanogenic reactors and freshwater environments, but also in marine environments, based upon extensive 16S rRNA gene-cloning analyses. In this study, we isolated an aceticlastic methanogen, designated strain 03d30qT, from a tidal flat sediment. Phylogenetic analyses based on 16S rRNA andmcrAgenes revealed that the isolate belongs to the genusMethanosaeta. Unlike the other knownMethanosaetaspecies, this isolate grows at Na+concentrations of 0.20 to 0.80 M, with an optimum concentration of 0.28 M. Quantitative estimation using real-time PCR detected the 16S rRNA gene of the genusMethanosaetain the marine sediment, and relative abundance ranged from 3.9% to 11.8% of the total archaeal 16S rRNA genes. In addition, the number ofMethanosaetaorganisms increased with increasing depth and was much higher than that ofMethanosarcinaorganisms, suggesting that aceticlastic methanogens contribute to acetate metabolism to a greater extent than previously thought in marine environments, where sulfate-reducing acetate oxidation prevails. This is the first report on marineMethanosaetaspecies, and based on phylogenetic and characteristic studies, the name “Methanosaeta pelagica” sp. nov. is proposed for this novel species, with type strain 03d30q.