Cold seeps, located along the Sonora Margin transform fault in the Guaymas Basin, were extensively explored during the 'BIG' cruise in June 2010. They present a seafloor mosaic pattern consisting of different faunal assemblages and microbial mats. To investigate this mostly unknown cold and hydrocarbon-rich environment, geochemical and microbiological surveys of the sediments underlying two microbial mats and a surrounding macrofaunal habitat were analyzed in detail. The geochemical measurements suggest biogenic methane production and local advective sulfate-rich fluxes in the sediments. The distributions of archaeal communities, particularly those involved in the methane cycle, were investigated at different depths (surface to 18 cm below the sea floor (cmbsf)) using complementary molecular approaches, such as Automated method of Ribosomal Intergenic Spacer Analysis (ARISA), 16S rRNA libraries, fluorescence in situ hybridization and quantitative polymerase chain reaction with new specific primer sets targeting methanogenic and anaerobic methanotrophic lineages. Molecular results indicate that metabolically active archaeal communities were dominated by known clades of anaerobic methane oxidizers (archaeal anaerobic methanotroph (ANME)-1, -2 and -3), including a novel 'ANME-2c Sonora' lineage. ANME-2c were found to be dominant, metabolically active and physically associated with syntrophic Bacteria in sulfate-rich shallow sediment layers. In contrast, ANME-1 were more prevalent in the deepest sediment samples and presented a versatile behavior in terms of syntrophic association, depending on the sulfate concentration. ANME-3 were concentrated in small aggregates without bacterial partners in a restricted sediment horizon below the first centimetres. These niche specificities and syntrophic behaviors, depending on biological surface assemblages and environmental availability of electron donors, acceptors and carbon substrates, suggest that ANME could support alternative metabolic pathways than syntrophic anaerobic oxidation of methane.

A deep-sea, facultatively anaerobic, heterotrophic, mesophilic new organism was isolated from the polychaete annelid Alvinella pompejana collected from a deep-sea hydrothermal field in the East Pacific Rise. On the basis of phenotypic characteristics, phylogenetic analyses, and DNA-DNA relatedness, this organism was identified as a new species of the genus Kbrio, for which the name Vibrio diabolicus is proposed. In batch cultures in the presence of glucose, this organism produced an innovative exopolysaccharide. This polymer had high contents of both uronic acids and hexosamines and was similar to other polysaccharides with interesting biological activities.Because of the interesting properties of polymers secreted by marine bacteria to enhance their survival in their natural environments, many scientists have isolated such bacteria and have characterized the exopolysaccharides (EPS) produced (2, 4, 14, [16][17][18]28). Since the discovery and exploration of many deep-sea hydrothermal ecosystems known for their extreme conditions, the search for EPS-secreting bacteria has been systematic (11,23,29). However, only a few EPS-secreting bacteria have been described (21,22,29,30), and all strains isolated previously from deep-sea hydrothermal ecosystems have been assigned to the genus Alteromonas. In the present study we describe the first Vibrio strain isolated from a deepsea hydrothermal vent and show that it is a member of a new species. MATERIALS AND METHODSBacterial strains. During the French-American cruise HERO in October 1991, samples of vent fluids, chimney rocks, invertebrate tissues, and seawater were collected by the French-manned submersible Nautile at a depth of 2,600 m in a rift system of the East Pacific Rise (8, 12) (12"48.13'N, 103"56.30'W). Samples were inoculated into marine 2216 broth (Difco Laboratories, Detroit, Mich.) at pH 7.6 and incubated at 25°C for 24 to 48 h. Enrichment cultures were purified on marine 2216 agar (Difco) by using the same growth conditions. Pure cultures were maintained in 20% (vol/vol) glycerol at -20 and -70°C for use in future experiments and in liquid nitrogen for long-term storage. Three bacterial strains were isolated from the dorsal integument of the hydrothermal vent polychaete annelid Alvinella pompejana (6), which was collected from a dense population of annelids near the active hydrothermal vent ELSA. While we were searching for marine EPS-secreting bacteria, isolate HE800T was selected because of its ability to exhibit the most interesting swarming mucoid phenotype on marine 2216 agar (Difco) supplemented with glucose (30 @liter) after 3 days at 25°C.Vibno nereis LMG 3895T and Wbrio tubiashii LMG 10936T were obtained from the LMG Culture Collection (Ghent, Belgium). Vibrio mytili CECT 632T was a gift from the Coleccion Espanola de Cultivos Tip0 (Universidad de Valencia, Burjassot, Spain).Cytological characterization. Gram staining was carried out as described by Conn et al. (5). Conventional transmission electron microscopy was used to observe strain HE800T an...

A deep-sea, aerobic, mesophilic and heterotrophic new bacterium was isolated from a sample of fluid collected among a dense population of Riftia pachyptila, in the vicinity of an active hydrothermal vent of the Southern depression of the Guaymas basin (Gulf of California). On the basis of phenotypic and phylogenetic analyses and DNA/DNA relatedness, the strain GY785 was recognized as a new species of the genus Alteromonas and the name of Alteromonas infernus is proposed. During the stationary phase in batch cultures in the presence of glucose, this bacterium secreted two unusual polysaccharides. The water-soluble exopolysaccharide-1 produced contained glucose, galactose, galacturonic and glucuronic acids as monosaccharides. The gel-forming exopolysaccharide-2 was separated from the bacterial cells by dialysis against distilled water and partially characterized.

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Caloranaerobacter azorensis gen. nov., sp. nov., an anaerobic thermophilic bacterium isolated from a deep-sea hydrothermal vent A thermophilic, anaerobic, chemo-organotrophic bacterium, designated MV1087 T , was isolated from a deep-sea hydrothermal chimney sample collected from the Mid-Atlantic Ridge. The cells were straight, motile and stained Gram-negative. Growth was observed from 45 to 65 SC, with an optimum around 65 SC. No growth was observed at 40 or 70 SC. Growth was observed from pH 55 to 90 and the optimum pH was around 7. The salinity range for growth was 10-100 g sea salt l N1 (corresponding to 65-65 g NaCl l N1 ) with an optimum at 30 g sea salt l N1 (20 g NaCl l N1 ). Strain MV1087 T was heterotrophic, able to ferment proteinaceous substrates, such as brain/heart infusion and gluten, and carbohydrates, such as glucose, xylan and starch. The DNA GMC content was 27 mol %. Phylogenetic analyses using 16S rDNA sequences indicated that strain MV1087 T belonged to cluster XII of the Clostridium subphylum. Due to its phenotypic and genotypic characteristics, isolate MV1087T is proposed as a novel species of a new genus, Caloranaerobacter azorensis gen. nov., sp. nov. The type strain is MV1087 T (l CNCM I-2543 T l DSM 13643 T ).

A deep-sea, aerobic, mesophilic, heterotrophic bacterium was isolated from fluid collected near an active hydrothermal vent. On the basis of phenotypic and phylogenetic analyses and DNA-DNA relatedness, strain ST716 could be assigned to the species Alteromonas macleodii as a new subspecies. This bacterium secreted an unusual high-molecular-weight polysaccharide in the presence of glucose in batch cultures. The viscosity of this exopolysaccharide is of the same order of magnitude as that of xanthan, another bacterial polysaccharide of industrial interest. This polysaccharide, produced during the stationary phase, contained glucose, mannose, pyruvated mannose, and galactose along with galacturonic acid and glucuronic acid.

The heterotrophic and mesophilic marine bacterium HYD-1545 was isolated on a metal-amended medium from the dorsal integument of the hydrothermal vent polychaete Alvinella pompejana. This strain, which can be assigned to the genus Alteromonas on the basis of its G+C content and phenotypical features, produced large amounts of an acidic polysaccharide in batch cultures. The polysaccharide was excreted during the stationary phase of growth and contained glucose, galactose, glucuronic acid, galacturonic acid, and 4,6-O-(1-carboxyethilidene)-galactose as major components. This polysaccharide was a polyelectrolyte, and the viscosity of its solutions depended on the ionic strength. The decrease in viscosity with increasing NaCl concentrations and the effect of Ca21 in decreasing the viscosity at low Ca2+ concentrations support a model in which the polysaccharide carries anionic groups. However, an unusual behavior was observed at higher concentrations and could be related to intermolecular interactions involving Ca2+ ions.

A thermophilic, anaerobic, chemo-organotrophic sulfur-reducing bacterium, designated MV1075 T , was isolated from a deep-sea hydrothermal chimney sample collected on the Mid-Atlantic Ridge. Cells were rod-shaped with a sheath-like outer structure, motile with polar flagella and stained Gramnegative. They appeared singly, in pairs or in short chains. The temperature range for growth was 25-65 SC, with an optimum at 55 SC. Growth was observed from pH 5 to pH 9, and the optimum pH was around 7. The salinity range for growth was 15-70 g sea salt l N1 (corresponding to 10-45 g NaCl l N1 ), with an optimum at 30 g l N1 (20 g NaCl l N1 ). The isolate was able to grow on a broad spectrum of carbohydrates or complex proteinaceous substrates. Sulfur was not necessary for growth. Growth was inhibited by H 2 , but, in presence of sulfur, this inhibition was removed and H 2 S was produced. The GMC content of the genomic DNA was 29 mol %. Phylogenetic analyses of the 16S rRNA gene located the strain within the order Thermotogales, in the domain Bacteria. On the basis of 16S rDNA sequence comparisons, in combination with morphological and physiological characteristics, it is proposed that the isolate should be described as a novel species of a new genus, Marinitoga gen. nov., of which Marinitoga camini sp. nov. is the type species. The type strain is MV1075 T (l CNCM I-2413T l DSM 13578 T ). Keywords : deep-sea hydrothermal vent, thermophile, Thermotogales, Marinitoga camini INTRODUCTIONThe order Thermotogales was first described as an order containing hyperthermophilic and extremely thermophilic bacteria (Huber & Stetter, 1992). This order was then expanded by the discovery of new species, extending both the temperature and salinity ranges for growth. Currently, it contains thermophilic bacteria growing at up to 90 mC, such as Thermotoga maritima, as well as moderate thermophiles such as Geotoga subterranea, which grows at an optimum temperature of 45 mC. The order Thermotogales is represented by five genera : Thermotoga, Thermosipho, Fervidobacterium, Geotoga and Petrotoga. The strains have various origins : oil-producing wells or oil reservoirs (Davey et al., 1993 ;Jeanthon et al., 1995 ;Ravot et al., 1995a ;Lien et al., 1998), geothermally heated continental waters (Patel et al., 1985 ;Windberger et al., 1989 ; Huber et al., 1990 ;Andrews & Patel, 1996 ;Friedrich & Antranikian, 1996) and geothermally heated marine waters (Huber et al., 1986Jannasch et al., 1988 ;Antoine et al., 1997). Duckworth et al. (1996) have also isolated an an- N. Wery and others aerobic thermophile from a soda lake, and have proposed that it could be assigned to a new genus within the order Thermotogales because of its 16S rDNA sequence and its alkaliphilic phenotype. Among the described species of the Thermotogales, only Thermosipho melanesiensis was isolated from deep-sea hydrothermal vents. It was isolated from the gills of a deep-sea hydrothermal vent mussel from the Lau Basin (south-western Pacific Ocean) (Antoine et al., 1997).Other anaerobic,...