Two novel strains of thermophilic planctomycetes were recovered from terrestrial and subterranean habitats. Strain R1^Twas isolated from a hot spring (Kunashir Island, Russia) and strain SBP2^Twas isolated from a deep gold mine (South Africa). Both isolates grew in the temperature range 30–60 °C and pH range 5.0–8.0. Strain R1^Tgrew optimally at 60 °C and pH 6.0–6.5; for SBP2^Toptimal conditions were at 52 °C and pH 7.5–8.0. Both strains were capable of anaerobic respiration with nitrate and nitrite as electron acceptors as well as of microaerobic growth. They also could grow by fermentation of mono-, di- and polysaccharides. Based on their phylogenetic position and phenotypic features we suggest that the new isolates represent two novel species belonging to a new genus in the order Planctomycetales , for which the namesThermogutta terrifontisgen. nov., sp. nov. andThermogutta hypogeasp. nov. are proposed. The type strain ofThermogutta terrifontis, the type species of the genus, is R1^T( = DSM 26237^T = VKM B-2805^T), and the type strain ofThermogutta hypogeais SBP2^T( = JCM 19991^T = VKM B-2782^T).

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).

A moderately thermophilic, anaerobic, dissimilatory iron(III)-reducing bacterium (strain S3R1^T) was isolated from a deep-sea hydrothermal vent chimney located on the Eastern Lau Spreading Centre in the Pacific Ocean at a depth of about 2150 m. Cells of strain S3R1^Twere ovals to short rods with a single polar flagellum, Gram-stain-negative, 0.5–0.6 µm in diameter and 0.8–1.3 µm long, growing singly or in pairs. The temperature range for growth was 36–62 °C, with an optimum at 50 °C. The pH range for growth was 5.5–7.5, with an optimum at pH 6.5. Growth of strain S3R1^Twas observed at NaCl concentrations ranging from 1.0 to 5.0 % (w/v), with an optimum at 2.0–2.5 % (w/v). The isolate used acetate, fumarate, malate, maleinate, succinate, propanol, palmitate, stearate, peptone and yeast extract as electron donors for growth and iron(III) reduction. All electron donors were oxidized completely to CO₂and H₂O. Iron(III) (in the form of ferrihydrite, ferric citrate or ferric nitrilotriacetate) and elemental sulfur (S⁰) were the electron acceptors that supported growth. The DNA G+C content was 64.4 mol%. Results of 16S rRNA gene sequence analysis showed that the novel bacterium was related to representatives of the orders Desulfuromonadales and Syntrophobacterales with 84–86 % sequence similarity and formed a distinct phylogenetic branch in the Deltaproteobacteria .On the basis of its physiological properties and results of phylogenetic analyses, it is proposed that the new isolate represents the sole species of a novel genus,Deferrisoma caminigen. nov., sp. nov. The type strain ofDeferrisoma caminiis S3R1^T( = DSM 24185^T = VKM B-2672^T).

An extremely thermophilic, anaerobic, chemolithoautotrophic bacterium (strain ST65T) was isolated from a deep-sea hydrothermal vent chimney located on the Eastern Lau Spreading Centre in the south-western Pacific Ocean, at a depth of 1870 m. Cells of strain ST65T were non-motile straight or slightly curved short rods, 0.5–0.6 µm in diameter and 0.8–1.5 µm in length. The temperature range for growth was 47–75 °C, with an optimum at 65 °C. The pH range for growth was 5.5–7.5, with an optimum at pH 6.5. Growth of strain ST65T was observed at NaCl concentrations ranging from 1.5 to 4.5 % (w/v), with an optimum at 2.0–2.5 %. Strain ST65T grew anaerobically with inorganic carbon as a carbon source and with elemental sulfur as an electron donor and nitrate as an electron acceptor producing sulfate and ammonium. It was also able to grow by disproportionation of elemental sulfur, thiosulfate and sulfite. Sulfate was not utilized as an electron acceptor. Analysis of the 16S rRNA gene sequence revealed that the isolate belongs to a deep lineage in the phylum Thermodesulfobacteria . On the basis of its physiological properties and results of phylogenetic analyses, it is proposed that the isolate represents a novel species of a new genus, Thermosulfuriphilus ammonigenes gen. nov., sp. nov. ST65T (=DSM 102941T=VKM B-2855T) is the type strain of the type species.