Miyazaki, Masayuki

The strain TOYAMA8T is a deep-sea alkaliphilic cellulolytic bacterium isolated from a slurry-adhered epiphytic site of Megalodicopia hians. Cells of this strain are Gram-negative, aerobic, curved rods or spirilla, motile with monopolar flagella, and grow on cellulose as the sole carbon source. Compared to other closely related species, this bacterium is characterized by a large number of cellulase genes. Strain TOYAMA8T showed alkaliphilic growth within the pH range 7.5–9.0. The major cellular fatty acids were C18 : 1 ω7, C14 : 0, C16 : 0 and C16 : 1 ω7. The major polar lipids were phosphatidylglycerol, phosphatidylethanolamine, unidentified phospholipids and aminolipids. A major respiratory lipoquinone was Q-9. Phylogenomic analysis using the 16S rRNA gene and whole-genome sequence data showed that the strain is related to the families Gynuellaceae, Saccharospirillaceae and Natronospirillaceae. The values of 16S rRNA gene sequence similarity, amino acid identity and percentage of conserved proteins between the strain TOYAMA8T and related species were low, with maximum values of 90.6, 48.1 and 34.6%, respectively. These results, together with differences in phenotypic and biochemical characteristics, indicate that the new isolate TOYAMA8T represents a novel genus and species, for which the name Marinicellulosiphila megalodicopiae gen. nov., sp. nov., is proposed. The type strain is TOYAMA8T (JCM 31119T=DSM 114864T).

An anaerobic, mesophilic, syntrophic, archaeon strain MK-D1T, was isolated as a pure co-culture with Methanogenium sp. strain MK-MG from deep-sea methane seep sediment. This organism is, to our knowledge, the first cultured representative of ‘Asgard’ archaea, an archaeal group closely related to eukaryotes. Here, we describe the detailed physiology and phylogeny of MK-D1T and propose Promethearchaeum syntrophicum gen. nov., sp. nov. to accommodate this strain. Cells were non-motile, small cocci, approximately 300–750 nm in diameter and produced membrane vesicles, chains of blebs and membrane-based protrusions. MK-D1T grew at 4–30 °C with optimum growth at 20 °C. The strain grew chemoorganotrophically with amino acids, peptides and yeast extract with obligate dependence on syntrophy with H2-/formate-utilizing organisms. MK-D1T showed the fastest growth and highest maximum cell yield when grown with yeast extract as the substrate: approximately 3 months to full growth, reaching up to 6.7×106 16S rRNA gene copies ml−1. MK-D1T had a circular 4.32 Mb chromosome with a DNA G+C content of 31.1 mol%. The results of phylogenetic analyses of the 16S rRNA gene and conserved marker proteins indicated that the strain is affiliated with ‘Asgard’ archaea and more specifically DHVC1/DSAG/MBG-B and ‘Lokiarchaeota’/‘Lokiarchaeia’. On the basis of the results of 16S rRNA gene sequence analysis, the most closely related isolated relatives were Infirmifilum lucidum 3507LTT (76.09 %) and Methanothermobacter tenebrarum RMAST (77.45 %) and the closest relative in enrichment culture was Candidatus ‘Lokiarchaeum ossiferum’ (95.39 %). The type strain of the type species is MK-D1T (JCM 39240T and JAMSTEC no. 115508). We propose the associated family, order, class, phylum, and kingdom as Promethearchaeaceae fam. nov., Promethearchaeales ord. nov., Promethearchaeia class. nov., Promethearchaeota phyl. nov., and Promethearchaeati regn. nov., respectively. These are in accordance with ICNP Rules 8 and 22 for nomenclature, Rule 30(3)(b) for validation and maintenance of the type strain, and Rule 31a for description as a member of an unambiguous syntrophic association.