A novel acidophilic, cell-wall-less archaeon, strain VT, was isolated from a hydrothermal pool on Vulcano Island, Italy. The morphology of cells was observed to vary from pleomorphic to coccoid. The temperature range for growth of strain VT was 15–65 °C with an optimum at 45 °C. The pH for growth ranged from pH 0 to 4 with an optimal at pH 1.4–1.6. Strain VT was able to grow aerobically and anaerobically, oxidizing ferrous iron and reducing ferric iron, respectively. The isolate grew chemo-organotrophically with yeast extract and yeast extract with glucose as the sources of energy and carbon. The molar G+C content in the DNA was 36 mol%. 16S rRNA gene sequence analysis demonstrated that strain VT was a member of the family Ferroplasmaceae, order Thermoplasmatales, phylum Euryarchaeota, showing sequence identities of 100 % with Ferroplasma cupricumulans BH2T, 95.4 % with Ferroplasma acidiphilum YT, 94 % with Picrophilus torridus DSM 9790T and 92 % with Picrophilus oshimae DSM 9789T. 16S rRNA gene sequence-based phylogenetic analysis showed that strain VT formed a monophyletic cluster together with F. cupricumulans BH2T and all other thermophilic isolates with available 16S rRNA gene sequences, whereas F. acidiphilum YT formed another cluster with mesophilic isolates within the family Ferroplasmaceae. DNA–DNA hybridization values between strain VT and F. cupricumulans BH2T were well below 70 %, indicating that the two strains belong to separate species. Principal membrane lipids of strain VT were dibiphytanyl-based tetraether lipids containing pentacyclic rings. The polar lipids were dominated by a single phosphoglycolipid derivative based on a galactosyl dibiphytanyl phosphoglycerol tetraether, together with smaller amounts of monoglycosyl and diglycosyl dibiphytanyl ether lipids and the corresponding phosphoglycerol derivatives. The major respiratory quinones present were naphthoquinone derivatives. Given the notable physiological and chemical differences as well as the distinct phylogenetic placement of the new isolate relative to the type species of the genus Ferroplasma, we propose strain VT as a member of a new genus and species, Acidiplasma aeolicum gen. nov.,
sp. nov. The type strain of Acidiplasma aeolicum is strain VT (=DSM 18409T =JCM 14615T). In addition, we propose to transfer Ferroplasma cupricumulans Hawkes et al. 2008 to the genus Acidiplasma as Acidiplasma cupricumulans comb. nov. (type strain BH2T =DSM 16551T =JCM 13668T).
A hyperthermophilic, anaerobic, dissimilatory Fe(III)-reducing, facultatively chemolithoautotrophic archaeon (strain SBH6T) was isolated from a hydrothermal sample collected from the deepest of the known World Ocean hydrothermal fields, Ashadze field (1 ° 58′ 21″ N 4 ° 51′ 47″ W) on the Mid-Atlantic Ridge, at a depth of 4100 m. The strain was enriched using acetate as the electron donor and Fe(III) oxide as the electron acceptor. Cells of strain SBH6T were irregular cocci, 0.3–0.5 μm in diameter. The temperature range for growth was 50–85 °C, with an optimum at 81 °C. The pH range for growth was 5.0–7.5, with an optimum at pH 6.8. Growth of SBH6T was observed at NaCl concentrations ranging from 1 to 6 % (w/v) with an optimum at 2.5 % (w/v). The isolate utilized acetate, formate, pyruvate, fumarate, malate, propionate, butyrate, succinate, glycerol, stearate, palmitate, peptone and yeast extract as electron donors for Fe(III) reduction. It was also capable of growth with H2 as the sole electron donor, CO2 as a carbon source and Fe(III) as an electron acceptor without the need for organic substances. Fe(III) [in the form of poorly crystalline Fe(III) oxide or Fe(III) citrate] was the only electron acceptor that supported growth. 16S rRNA gene sequence analysis revealed that the closest relative of the isolated organism was Geoglobus ahangari 234T (97.0 %). On the basis of its physiological properties and phylogenetic analyses, the isolate is considered to represent a novel species, for which the name Geoglobus acetivorans sp. nov. is proposed. The type strain is SBH6T (=DSM 21716T =VKM B-2522T).