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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 ).

As part of an ongoing examination of microbial diversity associated with hydrothermal vent polychaetes of the family Alvinellidae, we undertook a culture-independent molecular analysis of the bacterial assemblage associated with mucous secretions of the Northeastern Pacific vent polychaete Paralvinella palmiformis. Using a molecular 16S rDNA-based phylogenetic approach, clone libraries were constructed from two samples collected from active sulfide edifices in two hydrothermal vent fields. In both cases, clone libraries were largely dominated by epsilon-Proteobacteria. Phylotypes belonging to the Cytophaga-Flavobacteria and to the Verrucomicrobia were also largely represented within the libraries. The remaining sequences were related to the taxonomic groups Fusobacteria, Green non-sulfur bacteria, Firmicutes, gamma- and delta-Proteobacteria. To our knowledge, this is the first report of the presence of Verrucomicrobia, Fusobacteria and green non-sulfur bacteria on hydrothermal edifices. The potential functions of the detected bacteria are discussed in terms of productivity, recycling of organic matter and detoxification within the P. palmiformis microhabitat.

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,...

The Rimicaris exoculata shrimp is considered as a primary consumer that dominates the fauna of most Mid-Atlantic Ridge (MAR) hydrothermal ecosystems. These shrimps harbour in their gill chambers an important ec-tosymbiotic community of chemoautotrophic bacteria associated with iron oxide deposits. The structure and elemental composition of the mineral concretions associated with these bacteria have been investigated by using LM, ESEM, TEM STEM and EDX microanalyses. The nature of the iron oxides in shrimps obtained from the Rainbow vent field has also been determined by Mössbauer spectroscopy. This multidisciplinary approach has revealed that the three layers of mineral crust in the Rimicaris exoculata shrimps consist of large concretions formed by aggregated nanoparticles of two-line ferrihydrite and include other minor elements as Si, Ca, Mg, S and P, probably present as silicates cations, sul-phates or phosphates respectively that may contribute to sta-bilise the ferrihydrite form of iron oxides. TEM-observations on the bacteria have revealed their close interactions with these minerals. Abiotic and biotic precipitation could occur within the gill chamber of Rimicaris exoculata, suggesting the biologically-mediated formation of the iron oxide deposits. The difference of the bacterial density in the three-mineral crust layers could be correlated to the importance of the iron oxide concretions and suggest that the first mineral particles precipitates on the lower layer which could be considered as the most likely location of iron-oxidizing bacteria.