Tepidibacillus fermentans gen. nov., sp. nov.: a moderately thermophilic anaerobic and microaerophilic bacterium from an underground gas storage.

A novel moderately thermophilic bacterium, strain STGH(T), was isolated from Severo-Stavropolskoye underground gas storage (Russia). Cells of strain STGH(T) were spore-forming motile straight rods 0.3 µm in diameter and 2.0-4.0 µm in length having a Gram-positive cell wall structure. The temperature range for growth was 36-65 °C, with an optimum at 50-52 °C. The pH range for growth was 5.5-8.0, with an optimum at pH 7.0-7.5. Growth of strain STGH(T) was observed at NaCl concentrations ranging from 0 to 4.0 % (w/v) with an optimum at 1.0 % (w/v). Strain STGH(T) grew anaerobically by reduction of nitrate, thiosulfate, S(0) and AQDS using a number of complex proteinaceous compounds, organic acids and carbohydrates as electron donors. Nitrate was reduced to nitrite; thiosulfate and sulfur were reduced to sulfide. It also was able to ferment pyruvate, glucose, fructose, and maltose. The strain STGH(T) did not grow under aerobic conditions during incubation with atmospheric concentration of oxygen but was able to microaerobic growth (up to 10 % of oxygen in gas phase). The G+C content of DNA of strain STGH(T) was 34.8 mol%. 16S rRNA gene sequence analysis revealed that the isolated organism belongs to the class Bacilli. We propose to assign strain STGH(T) to a new species of a novel genus Tepidibacillus fermentans gen. nov., sp.nov. The type strain is STGH(T) (=DSM 23802(T), =VKM B-2671(T)).

Dissulfuribacter thermophilus gen. nov., sp. nov., a thermophilic, autotrophic, sulfur-disproportionating, deeply branching deltaproteobacterium from a deep-sea hydrothermal vent.

A thermophilic, anaerobic, chemolithoautotrophic bacterium (strain S69(T)) was isolated from a deep-sea hydrothermal vent chimney located on the Eastern Lau Spreading Center and Valu Fa Ridge, Pacific Ocean, at a depth of 1910 m using anoxic medium with elemental sulfur as the only energy source. Cells of strain S69(T) were Gram-negative short rods, 0.4-0.6 µm in diameter and 1.0-2.5 µm in length, motile with a single polar flagellum. The temperature range for growth was 28-70 °C, with an optimum at 61 °C. The pH range for growth was 5.6-7.9, with optimum growth at pH 6.8. Growth of strain S69(T) was observed at NaCl concentrations ranging from 0.9 to 5.0%, with an optimum at 1.8-2.7 (w/v). Strain S69(T) grew anaerobically with elemental sulfur as an energy source and bicarbonate/CO2 as a carbon source. Elemental sulfur was disproportionated to sulfide and sulfate. Growth was enhanced in the presence of poorly crystalline Fe(III) oxide (ferrihydrite) as a sulfide-scavenging agent. Strain S69(T) was also able to grow by disproportionation of thiosulfate and sulfite. Sulfate was not used as an electron acceptor either with H2 or with organic electron donors. Analysis of the 16S rRNA gene sequence revealed that the isolate formed a distinct phylogenetic branch within the Deltaproteobacteria. On the basis of its physiological properties and results of phylogenetic analyses, strain S69(T) is considered to represent a novel species of a new genus, for which the name Dissulfuribacter thermophilus gen. nov., sp. nov. is proposed. The type strain of Dissulfuribacter thermophilus is S69(T) (=DSM 25762(T)=VKM B-2760(T)).

Caloribacterium cisternae gen. nov., sp. nov., an anaerobic thermophilic bacterium from an underground gas storage reservoir.

A novel anaerobic, moderately thermophilic bacterium (strain SGL43(T)) was isolated from Severo-Stavropolskoye underground gas storage reservoir (Russia). Cells of strain SGL43(T) were motile straight rods, 0.4 µm in diameter and 2.0-3.0 µm in length. The temperature range for growth was 28-65 °C, with optimum growth at 50 °C. The pH range for growth was 5.5-8.0, with optimum growth at pH 7.0-7.5. Growth of strain SGL43(T) was observed at NaCl concentrations of 0-4.0% (w/v) with optimum growth at 1.0% (w/v) NaCl. Substrates utilized by strain SGL43(T) included peptone, yeast extract, glucose, fructose, maltose, galactose, pyruvate and citrate. Products of glucose or citrate fermentation were acetate, hydrogen and CO(2). Thiosulfate was reduced to sulfide. The DNA G+C content of strain SGL43(T) was 43.1 mol%. 16S rRNA gene sequence analysis revealed that strain SGL43(T) belongs to the order Thermoanaerobacterales (phylum 'Firmicutes'). The closest relative of strain SGL43(T) was Thermoanaerobacterium saccharolyticum (86.2% 16S rRNA gene sequence similarity with the type strain). Based on the data presented here, strain SGL43(T) is considered to represent a novel species of a new genus, for which the name Caloribacterium cisternae gen. nov., sp. nov. is proposed. The type strain of Caloribacterium cisternae, the type species of the genus, is SGL43(T) (=DSM 23830(T)=VKM B-2670(T)).

Deferrisoma camini gen. nov., sp. nov., a moderately thermophilic, dissimilatory iron(III)-reducing bacterium from a deep-sea hydrothermal vent that forms a distinct phylogenetic branch in the Deltaproteobacteria.

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(T) were 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(T) was 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 CO(2) and H(2)O. Iron(III) (in the form of ferrihydrite, ferric citrate or ferric nitrilotriacetate) and elemental sulfur (S(0)) 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 camini gen. nov., sp. nov. The type strain of Deferrisoma camini is S3R1(T) ( = DSM 24185(T)  = VKM B-2672(T)).

Thermosulfurimonas dismutans gen. nov., sp. nov., an extremely thermophilic sulfur-disproportionating bacterium from a deep-sea hydrothermal vent.

An extremely thermophilic, anaerobic, chemolithoautotrophic bacterium (strain S95(T)) was isolated from a deep-sea hydrothermal vent chimney located on the Eastern Lau Spreading Center, Pacific Ocean, at a depth of 1910 m. Cells of strain S95(T) were oval to short Gram-negative rods, 0.5-0.6 µm in diameter and 1.0-1.5 µm in length, growing singly or in pairs. Cells were motile with a single polar flagellum. The temperature range for growth was 50-92 °C, with an optimum at 74 °C. The pH range for growth was 5.5-8.0, with an optimum at pH 7.0. Growth of strain S95(T) was observed at NaCl concentrations ranging from 1.5 to 3.5% (w/v). Strain S95(T) grew anaerobically with elemental sulfur as an energy source and bicarbonate/CO(2) as a carbon source. Elemental sulfur was disproportionated to sulfide and sulfate. Growth was enhanced in the presence of poorly crystalline iron(III) oxide (ferrihydrite) as a sulfide-scavenging agent. Strain S95(T) was also able to grow by disproportionation of thiosulfate and sulfite. Sulfate was not used as an electron acceptor. Analysis of the 16S rRNA gene sequence revealed that the isolate belongs to the phylum Thermodesulfobacteria. On the basis of its physiological properties and results of phylogenetic analyses, it is proposed that the isolate represents the sole species of a new genus, Thermosulfurimonas dismutans gen. nov., sp. nov.; S95(T) (=DSM 24515(T)=VKM B-2683(T)) is the type strain of the type species. This is the first description of a thermophilic micro-organism that disproportionates elemental sulfur.

Isolation of the anaerobic thermoacidophilic crenarchaeote Acidilobus saccharovorans sp. nov. and proposal of Acidilobales ord. nov., including Acidilobaceae fam. nov. and Caldisphaeraceae fam. nov.

An anaerobic acidophilic, hyperthermophilic archaeon, designated strain 345-15(T), was isolated from an acidic hot spring of Kamchatka (Russia). Cells of strain 345-15(T) were regular or irregular cocci, 1-2 mum in diameter, with flagella. Strain 345-15(T) grew optimally at 80-85 degrees C and pH 3.5-4.0 and fermented a wide range of carbohydrates, including polysaccharides. Acetate, ethanol and lactate were the fermentation products. Growth was stimulated by elemental sulfur and thiosulfate, which were reduced to hydrogen sulfide. The G+C content of the DNA was 54.5 mol%. The 16S rRNA gene sequence analysis indicated that strain 345-15(T) belonged to the genus Acidilobus. The level of DNA-DNA hybridization between strain 345-15(T) and Acidilobus aceticus 1904(T) was 61 %. Thus, strain 345-15(T) was considered as representing a novel species of the genus Acidilobus, with the name Acidilobus saccharovorans sp. nov. (type strain, 345-15(T)=DSM 16705(T)=VKM B-2471(T)), which shared the main morphological and physiological properties of the genus but differed by the presence of flagella and the spectrum of substrates utilized. Phylogenetic analysis showed that the genus Acidilobus, with its species Acidilobus aceticus, Acidilobus saccharovorans sp. nov. and 'Acidilobus sulfurireducens', and the genus Caldisphaera, represented by Caldisphaera lagunensis and 'Caldisphaera draconis', formed a separate cluster that adjoins the cluster formed by the species of the order Desulfurococcales. Members of the Acidilobus-Caldisphaera cluster are thermophilic, organotrophic anaerobic cocci that can be distinguished from all species of the order Desulfurococcales on the basis of acidophily. Based on these considerations, we propose a new family, Acidilobaceae fam. nov., to accommodate the subcluster of hyperthermophiles represented by the genus Acidilobus, a new family, Caldisphaeraceae fam. nov., for the subcluster of extreme thermophiles represented by the genus Caldisphaera, and a new order, Acidilobales ord. nov., to accommodate the two new families.

Clostridium tepidiprofundi sp. nov., a moderately thermophilic bacterium from a deep-sea hydrothermal vent.

A moderately thermophilic, anaerobic bacterium (strain SG 508T) was isolated from a hydrothermal vent chimney located at 1 degrees N on the East Pacific Rise at a depth of 2650 m. Cells of strain SG 508T were straight to slightly curved rods, 0.4-0.6 microm in diameter and 2.0-3.0 microm in length. Spore formation was observed only below pH 5.5. The temperature range for growth was 22-60 degrees C, with optimum growth at 50 degrees C. The pH range for growth was 4.0-8.5, with optimum growth at pH 6.0-6.8. Growth of strain SG 508T was observed at NaCl concentrations ranging from 1.0 to 6.0 % (w/v), with optimum growth at 2.5 % (w/v). Substrates utilized by strain SG 508T included casein, peptone, tryptone, yeast extract, beef extract, starch, maltose and glucose. The products of glucose fermentation were ethanol, acetate, H2, formate and CO2. Strain SG 508T was able to reduce elemental sulfur to hydrogen sulfide. The DNA G+C content of strain SG 508T was 30.9 mol%. 16S rRNA gene sequence analysis revealed that the isolated organism belonged to cluster I of the genus Clostridium. On the basis of its physiological properties and data from phylogenetic analyses, strain SG 508T is considered to represent a novel species of the genus Clostridium, for which the name Clostridium tepidiprofundi sp. nov. is proposed. The type strain is SG 508T (=DSM 19306T =VKM B-2459T).

Thermoanaerobacterium aciditolerans sp. nov., a moderate thermoacidophile from a Kamchatka hot spring.

An anaerobic, moderately thermoacidophilic bacterium, strain 761-119T, was isolated from an acidic hot spring in the Orange Field of the Uzon Caldera (Kamchatka, far-eastern Russia). Cells were spore-forming, Gram-positive rods, possessing one polar flagellum. Growth of strain 761-119T was observed between 37 and 68 degrees C and in the pH(20 degrees C) range 3.2-7.1. No growth was observed within 5 days of incubation at or below 35 degrees C and at or above 70 degrees C, as well as at or below pH(20 degrees C) 2.8 and at or above pH(20 degrees C) 7.5. The optimal temperature and pH(20 degrees C) for growth were 55 degrees C and pH(20 degrees C) 5.7, respectively. A wide range of carbohydrates and polysaccharides were fermented, as well as peptides and proteinaceous substrates. The main products of glucose fermentation were acetate, ethanol, lactate, H2 and CO2. The DNA G+C content was 34 (+/-0.5) mol%. 16S rRNA gene sequence analysis indicated that strain 761-119T belonged to the genus Thermoanaerobacterium. The level of 16S rRNA gene sequence similarity with other Thermoanaerobacterium species was 86.5-97.8 %, with the only moderately acidophilic member of this genus, Thermoanaerobacterium aotearoense, being one of its closest relatives. DNA-DNA hybridization with T. aotearoense showed 33 % relatedness. Thus, morphological (one polar flagellum) and physiological characteristics (lower pH limit of growth at pH(20 degrees C) 3.2 compared with T. aotearoense) and 16S rRNA gene sequence analyses revealed that strain 761-119T represents a novel species in the genus Thermoanaerobacterium, for which the name Thermoanaerobacterium aciditolerans sp. nov. is proposed, with the type strain 761-119T (=DSM 16487T=VKM B-2363T).

Vulcanibacillus modesticaldus gen. nov., sp. nov., a strictly anaerobic, nitrate-reducing bacterium from deep-sea hydrothermal vents.

A novel anaerobic, moderately thermophilic, spore-forming bacterium, designated strain BRT, was isolated from deep-sea hydrothermal core samples collected at the Rainbow vent field on the Mid-Atlantic Ridge (36 degrees 14' N 33 degrees 54' W). The cells were found to be rod-shaped, non-motile, Gram-positive and spore-forming. The organism grew in the temperature range 37-60 degrees C, with an optimum at 55 degrees C, and at pH values in the range 6-8.5, with an optimum around pH 7. NaCl concentrations for growth were in the range 10-40 g l(-1), with an optimum at 20-30 g l(-1). Strain BRT grew chemo-organoheterotrophically with carbohydrates, proteinaceous substrates and organic acids with nitrate as electron acceptor. The novel isolate was not able to ferment. The G+C content of the genomic DNA was 34.5 mol%. Phylogenetic analysis of the 16S rRNA gene sequence placed strain BRT in the Bacillaceae within the class 'Bacilli'. On the basis of the phenotypic and phylogenetic data, this isolate should be described as a member of a novel genus, for which the name Vulcanibacillus gen. nov. is proposed. The type species is Vulcanibacillus modesticaldus sp. nov., with the type strain BRT (=DSM 14931T=JCM 12998T).

Tepidimicrobium ferriphilum gen. nov., sp. nov., a novel moderately thermophilic, Fe(III)-reducing bacterium of the order Clostridiales.

A moderately thermophilic, anaerobic bacterium (strain SB91T) was isolated from a freshwater hot spring at Barguzin Valley, Buryatiya, Russia. Cells of strain SB91T were straight to slightly curved rods, 0.5-0.6 microm in diameter and 3.0-7.0 mum in length. Formation of endospores was not observed. The temperature range for growth was 26-62 degrees C, with an optimum at 50 degrees C. The pH range for growth was 5.5-9.5, with an optimum at pH 7.5-8.0. The substrates utilized by strain SB91T in the presence of 9,10-anthraquinone 2,6-disulfonate included peptone, tryptone, Casamino acids, yeast extract, beef extract, casein hydrolysate, alanine plus glycine, alanine plus proline, L-valine and n-propanol. Carbohydrates were not utilized. Strain SB91T reduced amorphous Fe(III) oxide, Fe(III) citrate, Fe(III) EDTA or Fe(III) nitrilotriacetate with peptone, L-valine or n-propanol as an electron donor. Strain SB91T reduced 9,10-anthraquinone 2,6-disulfonate, thiosulfate, elemental sulfur, fumarate and selenite. Strain SB91T survived after exposure to gamma-radiation at a dose of 5.4 kGy. The G+C content of the DNA of strain SB91T was 33 mol%. Analysis of the 16S rRNA gene sequence revealed that the isolated organism belonged to cluster XII of the clostridia. On the basis of its physiological properties and the results of phylogenetic analyses, it is proposed that strain SB91T represents the sole species of a novel genus, Tepidimicrobium; the name Tepidimicrobium ferriphilum gen. nov., sp. nov. is proposed, with strain SB91T (=DSM 16624T=VKM B-2348T) as the type strain.

[Geoalkalibacter ferrihydriticus gen. nov., sp. nov., the first alkaliphilic representative of the family Geobacteraceae, isolated from a soda lake].

Investigation of iron reduction in bottom sediments of alkaline soda lakes resulted in the isolation of a new obligately anaerobic iron-reducing bacterium, strain Z-0531, from Lake Khadyn (Tuva Republic, Russia) sediment samples. The cells of strain Z-0531 are short (1.0-1.5 by 0.3-0.5 microm), motile, non-spore-forming, gram-negative rods. The isolate is an obligate alkaliphile, developing in the pH range of 7.8-10.0, with an optimum at pH 8.6. It does not require NaCl but grows at NaCl concentrations of 0-50 g/1l. It can oxidize acetate with such electron acceptors as amorphous Fe(llI) hydroxide (AFH), EDTA-Fe(III), anthraquinone-2,6-disulfonate (quinone), Mn(IV), and S(0). On media with EDTA-Fe(III), the isolate can oxidize, apart from acetate, ethanol, pyruvate, oxalate, arginine, tartrate, lactate, propionate, and serine. H2 is not utilized. The reduced products formed during growth with AFH are siderite or magnetite, depending on the growth conditions. The isolate is incapable of fermenting sugars, peptides, and amino acids. Yeast extract or vitamins are required as growth factors. The organism is capable of dinitrogen fixation and harbors the nifH gene. The DNA G+C content is 55.3 mol %. 16S rRNA analysis places strain Z-0531 into the family Geobacteraceae. Its closest relative (93% similarity) is Desulfuromonas palmitatis. Based on phenotypic distinctions and phylogenetic position, it is proposed that strain Z-0531 be assigned to the new genus and species Geoalkalibacter ferrihydriticus gen. nov., sp. nov.

[Clostridium alkalicellum sp. nov., an obligately alkaliphilic cellulolytic bacterium from a soda lake in the Baikal region].

The first anaerobic alkaliphilic cellulolytic microorganism has been isolated from the Verkhnee Beloe soda lake (Buryatiya, Russia) with pH 10.2 and a salt content of up to 24 g/l. Five strains were characterized. Strain Z-7026 was chosen as the type strain. The cells of the isolate are gram-positive spore-forming rods. A mucous external capsule is produced. The microorganism is obligately alkaliphilic, growing in a pH range of 8.0-10.2, with an optimum at pH 9.0. Sodium ions and, in carbonate-buffered media, sodium chloride are obligately required. The microorganism is slightly halophilic; it grows at 0.017-0.4 M Na+ with an optimum at 0.15-0.3 M Na+. The metabolism is fermentative and strictly anaerobic. Cellulose, cellobiose, and xylan can be used as growth substrates. Plant and algal debris can be fermented. Lactate, ethanol, acetate, hydrogen, and traces of formate are produced during cellulose or cellobiose fermentation. Yeast extract or vitamins are required for anabolic purposes. The microorganism fixes dinitrogen and is nitrogenase-positive. It is tolerant to up to 48 mM Na2S. Growth is not inhibited by kanamycin or neomycin. Chloramphenicol, streptomycin, penicillin, ampicillin, ampiox, bacillin, novobiocin, and bacitracin suppress growth. The DNA G+C content is 29.9 mol %. According to the nucleotide sequence of its 16S rRNA gene, strain Z-7026 is phylogenetically close to the neutrophilic cellulolytic bacteria Clostridium thermocellum (95.5%), C. aldrichii (94.9%), and Acetivibrio cellulolyticus (94.8%). It is proposed as a new species: Clostridium alkalicellum sp. nov.

Desulfurococcus fermentans sp. nov., a novel hyperthermophilic archaeon from a Kamchatka hot spring, and emended description of the genus Desulfurococcus.

An obligately anaerobic, hyperthermophilic, organoheterotrophic archaeon, strain Z-1312(T), was isolated from a freshwater hot spring of the Uzon caldera (Kamchatka Peninsula, Russia). The cells were regular cocci, 1-4 microm in diameter, with one long flagellum. The cell envelope was composed of a globular layer attached to the cytoplasmic membrane. The temperature range for growth was 63-89 degrees C, with an optimum between 80 and 82 degrees C. The pH range for growth at 80 degrees C was 4.8-6.8, with an optimum at pH 6.0. Strain Z-1312(T) grew by hydrolysis and/or fermentation of a wide range of polymeric and monomeric substrates, including agarose, amygdalin, arabinose, arbutin, casein hydrolysate, cellulose (filter paper, microcrystalline cellulose, carboxymethyl cellulose), dextran, dulcitol, fructose, lactose, laminarin, lichenan, maltose, pectin, peptone, ribose, starch and sucrose. No growth was detected on glucose, xylose, mannitol or sorbitol. Growth products when sucrose or starch were used as the substrate were acetate, H(2) and CO(2). Elemental sulfur, thiosulfate and nitrate added as potential electron acceptors for anaerobic respiration did not stimulate growth when tested with starch as the substrate. H(2) at 100 % in the gas phase did not inhibit growth on starch or peptone. The G+C content of the DNA was 42.5 mol%. 16S rRNA gene sequence analysis placed the isolated strain Z-1312(T) as a member of the genus Desulfurococcus, where it represented a novel species, for which the name Desulfurococcus fermentans sp. nov. (type strain Z-1312(T) = DSM 16532 (T) = VKM V-2316(T)) is proposed.

[Detection of a cultivated hyperthermophilic archaeon of the genus Sulfophobococcus in a methane tank operated in a thermophilic regime]. / Obnaruzhenie kul'tiviruemoi gipertermofil'noi arkhei roda Sulfophobococcus v metatanke, rabotaiushchem v termofil'nom rezhime.

A stable association of hyperthermophilic microorganisms (82 degrees C), which contained mostly cocci and a minor amount of non-spore-forming rods, was obtained from the fermented sludge of a methane tank used to process municipal wastewaters under thermophilic conditions (50 degrees C). PCR amplification of 16S rRNA genes using total DNA isolated from this association and archaea-specific primers, followed by sequencing of the product obtained, showed that the archaeal component was represented by a single nucleotide sequence, which was 99.9% homologous to 16S rRNA gene of Sulfophobococcus zilligii. Thus, a hyperthermophilic archaeon was for the first time detected in a system of anaerobic biological treatment of wastewater. In addition, this is the first report on the detection of a cultivated member of Crenarchaeota in anthropogenic habitats with neutral pH.

[Halomonas campisalis, an obligatorily alkaliphilic, nitrous oxide-reducing denitrifier with a Mo-cofactor-lacking nitrate reductase]. / Obligatno alkalofil'nyi denitrifikator Halomonas campisalis iz ozera Magadi, sposobnyi k vosstanovleniiu zakisi azota i lishennyi molibdenovogo kofaktora v sostave nitratreduktazy.

We isolated eight strains of denitrifying bacteria that reduce nitrate and nitrous oxide at pH 10 from Lake Magadi (Kenya). Despite certain differences between the strains, they are similar in terms of G+C content (66.1-68.1 mol %) and DNA-DNA homology (75-92%) and represent different morphotypes of the same species. Based on the results of partial 16S rRNA sequencing, strain Z-7398-2 was most closely related to the Halomonas campisalis isolate from Alkali Lake (USA). The DNA-DNA homology level between the tested strain and the type strain of H. campisalis 4A was 88%. These two strains were also similar phenotypically. However, the culture isolated by us was characterized by peculiar properties, such as obligate alkaliphily, which manifested itself in the culture dependence on carbonates and lack of growth at pH values below 7, a nitrous oxide-reducing capacity, and an unusual nitrate reductase that lacked molybdenum and a Mo cofactor.

Deferribacter abyssi sp. nov., an anaerobic thermophile from deep-sea hydrothermal vents of the Mid-Atlantic Ridge.

Two strains of thermophilic, anaerobic, chemolithoautotrophic bacteria, designated JR(T) and DR, were isolated from hydrothermal samples collected on the Mid-Atlantic Ridge from the Rainbow (36 degrees 16' N, 33 degrees 54' W) and Menez Gwen (37 degrees 50' N, 31 degrees 50' W) vent fields, respectively. Cells of both isolates were short, straight- to vibrio-shaped, motile rods with one polar flagellum, and were Gram-negative and non-sporulating. Strain JR(T) was characterized in detail. It was found to grow optimally at pH 6.5-6.7, at 60 degrees C and in the presence of 30 g NaCl l(-1). Strain JR(T) could use molecular hydrogen, acetate, succinate, pyruvate and proteinaceous compounds as electron donors, and elemental sulfur, nitrate or Fe(III) as electron acceptors. No fermentation of organic substrates occurred. The G+C content of the DNA of strain JR(T) was 30.8 mol%. Strain DR (=DSM 14927) possessed the same morphology and pH, temperature and salinity optima and ranges, and used the same electron acceptors as strain JR(T). On the basis of their 16S rDNA sequences (1517 nucleotides), strains JR(T) and DR were identical and distantly related to Deferribacter thermophilus and Deferribacter desulfuricans (95.3 and 95.2 % sequence similarity, respectively). Based on their phenotypic and phylogenetic characteristics, it is proposed that both strains are members of a new species of the genus Deferribacter, for which the name Deferribacter abyssi (type strain JR(T)=DSM 14873(T)=JCM 11955(T)) is proposed.

Tepidibacter thalassicus gen. nov., sp. nov., a novel moderately thermophilic, anaerobic, fermentative bacterium from a deep-sea hydrothermal vent.

A moderately thermophilic, anaerobic, endospore-forming bacterium (strain SC 562T) was isolated from a hydrothermal vent chimney located at 13 degrees N on the East-Pacific Rise at a depth of 2650 m. Cells of strain SC 562T were straight to slightly curved rods, which were 0.7-0.9 microm in diameter and 3.5-6.0 microm in length with peritrichous flagella. Strain SC 562T formed round, refractile endospores in terminally swollen sporangia. The temperature range for growth was 33-60 degrees C, with an optimum at 50 degrees C. The pH range for growth was 4.8-8.5, with an optimum at pH 6.5-6.8. Growth of strain SC 562T was observed at NaCl concentrations ranging from 1.5 to 6% (w/v). The substrates utilized by strain SC 562T included casein, peptone, albumin, yeast extract, beef extract, alanine plus proline and starch. Glucose, maltose, pyruvate, valine and arginine each slightly stimulated growth in the presence of yeast extract. The products of glucose fermentation were ethanol, acetate, H2 and CO2. Strain SC 562T reduced elemental sulfur to hydrogen sulfide. The G + C content of the DNA of strain SC 562T was 24 mol%. 16S rDNA sequence analysis revealed that the isolated organism belonged to cluster XI of the Clostridium subphylum. On the basis of its physiological properties and phylogenetic analyses, it is proposed that strain SC 562T represents the sole species of a novel genus, Tepidibacter; the name Tepidibacter thalassicus is proposed for strain SC 562T (=DSM 15285T=UNIQEM 215T).