The deep-sea floor encompasses more than half of the surface of our planet, yet the extent and distribution of deep-sea biodiversity and its contribution to large biogeochemical cycles remain poorly understood. This knowledge gap stems from several factors, including sampling issues, the magnitude of the work required for morphological inventories, and the difficulty of integrating results from disparate local studies. The application of meta-omics to environmental DNA now makes it possible to assemble interoperable datasets at different spatial scales to move towards a global assessment of deep-sea biodiversity. We present a large-scale dataset on deep-sea biodiversity, with data and metadata openly accessible at ENA and Zenodo. The resource was generated using standardized protocols developed according to FAIR principles, covering fieldwork through bioinformatic analysis, within “Pourquoi Pas les Abysses?” and eDNAbyss projects. Together with information ensuring reproducibility, this dataset —combining metagenomics, metabarcoding across the Tree of Life and capture-by-hybridization— contributes to the international concerted effort to achieve a holistic view of the biodiversity in the largest biome on Earth.

This study investigates minerals and microorganisms effects on fluid chemistry through a continuous enrichment culture in a gas-lift bioreactor during the MoMARsat'19 cruise. A sulfate-based chimney and buoyant hydrothermal fluid, both collected in situ at the Aisics vent of the Lucky Strike hydrothermal field, were incubated for 18 days under physico-chemical conditions simulating those of diffuse hydrothermal vents. We present the evolution of elemental and Sr, and Li isotopic compositions of the bioreactor fluid, alongside Bacteria and Archaea diversity, and analyze the mineral saturation state of the fluid through geochemical modeling. Our results show that the microbial diversity in the bioreactor reflects that of the sulfate-based chimney. During the initial 168 h, minerals precipitation/dissolution primarily controlled the elemental and Sr isotopic composition of the fluid. From 168 h to 264 h, sulfate-reducing Archaea (Archaeoglobi) disappeared in favor of sulfurreducing Archaea (Thermoprotei and Thermococci). This shift coincides with a drastic increase in trace element concentrations and less radiogenic 87Sr/86Sr ratios, suggesting a possible microbial influence on the fluid. From 264 h onwards, with stable sulfur-reducing archaeal diversity, mineral saturation state primarily controls the elemental composition of the fluid. However, the observed increase in the 87Sr/86Sr ratio and delta 7Li correlates with changes in bacterial diversity, notably an increase in Deinococci abundance. This study reveals that in a bioreactor simulating diffuse vent environments related to the sulfur cycle: (i) both microorganism and mineral influence fluid chemistry over time, (ii) shift in microbial diversity appear to affect trace metal concentrations and isotopic signatures, and (iii) the 87Sr/86Sr ratio serves as a tracer for mineral-fluid interactions and may be a tracer for microorganism-fluid interactions.

Background: In deep-sea hydrothermal vent areas, deprived of light, most animals rely on chemosynthetic symbionts for their nutrition. These symbionts may be located on their cuticle, inside modified organs, or in specialized cells. Nonetheless, many of these animals have an open and functional digestive tract. The vent shrimp Rimicaris exoculata is fueled mainly by its gill chamber symbionts, but also has a complete digestive system with symbionts. These are found in the shrimp foregut and midgut, but their roles remain unknown. We used genome-resolved metagenomics on separate foregut and midgut samples, taken from specimens living at three contrasted sites along the Mid-Atlantic Ridge (TAG, Rainbow, and Snake Pit) to reveal their genetic potential. Results: We reconstructed and studied 20 Metagenome-Assembled Genomes (MAGs), including novel lineages of Hepatoplasmataceae and Deferribacteres, abundant in the shrimp foregut and midgut, respectively. Although the former showed streamlined reduced genomes capable of using mostly broken-down complex molecules, Deferribacteres showed the ability to degrade complex polymers, synthesize vitamins, and encode numerous flagellar and chemotaxis genes for host-symbiont sensing. Both symbionts harbor a diverse set of immune system genes favoring holobiont defense. In addition, Deferribacteres were observed to particularly colonize the bacteria-free ectoperitrophic space, in direct contact with the host, elongating but not dividing despite possessing the complete genetic machinery necessary for this. Conclusion: Overall, these data suggest that these digestive symbionts have key communication and defense roles, which contribute to the overall fitness of the Rimicaris holobiont.

A novel thermophilic, microaerophilic and anaerobic, hydrogen- sulphur- and thiosulphate-oxidising bacterium, designated MO1340(T), was isolated from a deep-sea hydrothermal chimney collected from the Lucky Strike hydrothermal vent field on the Mid-Atlantic Ridge. Cells were short, motile rods of 1.4-2.2 mu m length and 0.5-0.8 mu m width. Optimal growth was observed for a NaCl concentration of 2.5 % (w/v) at pH 6.5. As for other members of the genus Persephonella, strain MO1340(T) was strictly chemolithoautotrophic and could oxidise hydrogen, elemental sulphur or thiosulphate using oxygen as electron acceptor. Anaerobic nitrate reduction using hydrogen could also be performed. Each catabolic reaction had a different optimal growth temperature (65 to 75 degrees C) and an optimal dissolved oxygen concentration (11.4 to 119.7 mu M at 70 degrees C for aerobic reactions) that varied according to the electron donors utilised. These experimental results are consistent with the distribution of these catabolic substrates along the temperature gradient observed in active hydrothermal systems. They strongly suggest that this adaptive strategy could confer a selective advantage for strain MO1340(T) in the dynamic part of the ecosystem where hot, reduced hydrothermal fluid mixes with cold, oxygenated seawater. Phylogenetic analysis indicated that strain MO1340(T) was a member of the genus Persephonella within the order Hydrogenothermales as it shared a 16S rRNA gene sequence similarity <95.5 % and ANI respectively 75.66 % with closest described Persephonella (P. hydrogeniphila 29W(T)). On the basis of the physiological and genomic properties of the new isolate, the name Persephonella atlantica sp. nov. is proposed. The type strain is MO1340(T) (=UBOCC-M-3359(T) =JCM 34026(T)). (C) 2021 Elsevier GmbH. All rights reserved.

The mixing zone between high‐temperature hydrothermal fluids and seawater produces redox gradients, promoting the development of unique ecosystems based on chemotrophy. The structure of microbial communities depends on their environment, which can vary according to space and time. Hydrothermal circulation within the oceanic crust determines the chemical composition and flow of fluids, depending on underground events (earthquakes, volcanic episodes, etc.) and impacts the development of microbial communities. This link between hydrothermal vent communities and deep geological events is the focus of the present study, the first of its kind for slow‐spreading ridge. In this study, we present a unique set of multidisciplinary data collected from 2008 to 2011 on the Eiffel Tower hydrothermal site (Lucky Strike vent field, Mid‐Atlantic Ridge, MAR). We benefit from continuous geophysical monitoring (temperature and seismicity) of the site, annual sampling of hydrothermal fluids (hot and diffuse) for geochemistry analyses, sampling of hydrothermal chimneys, and an in situ microbial colonization experiment over a year for microbial study. The high CO 2 content and concentrations of major elements (Cl, Ca, and Si) and SO 4 in the end‐member fluids collected in 2010 indicate that a magmatic degassing occurred between 2009 and 2010 under the Lucky Strike hydrothermal field. This is supported by the large temperature variations observed in March–April 2010. These magmatic CO 2 inputs seem to have affected microbial communities colonizing the high‐temperature chimney, as well as the basalts in the more diffuse and mixed zone, promoting the development of thermophilic/anaerobic Archaea and Bacteria (Archaeoglobales, Nautiliales, and Nitratiruptoraceae).

MarsiteCruise was undertaken in October/November 2014 in the Sea of Marmara to gain detailed insight into the fate of fluids migrating within the sedimentary column and partially released into the water column. The overall objective of the project was to achieve a more global understanding of cold-seep dynamics in the context of a major active strike-slip fault. Five remotely operated vehicle (ROV) dives were performed at selected areas along the North Anatolian Fault and inherited faults. To efficiently detect, select and sample the gas seeps, we applied an original procedure. It combines sequentially (1) the acquisition of ship-borne multibeam acoustic data from the water column prior to each dive to detect gas emission sites and to design the tracks of the ROV dives, (2) in situ and real-time Raman spectroscopy analysis of the gas stream, and (3) onboard determination of molecular and isotopic compositions of the collected gas bubbles. The in situ Raman spectroscopy was used as a decision-making tool to evaluate the need for continuing with the sampling of gases from the discovered seep, or to move to another one. Push cores were gathered to study buried carbonates and pore waters at the surficial sediment, while CTD-Rosette allowed collecting samples to measure dissolved-methane concentration within the water column followed by a comparison with measurements from samples collected with the submersible Nautile during the Marnaut cruise in 2007. Overall, the visited sites were characterized by a wide diversity of seeps. CO2- and oil-rich seeps were found at the westernmost part of the sea in the Tekirdag Basin, while amphipods, anemones and coral populated the sites visited at the easternmost part in the Cinarcik Basin. Methane-derived authigenic carbonates and bacterial mats were widespread on the seafloor at all sites with variable size and distributions. The measured methane concentrations in the water column were up to 377 mu mol, and the dissolved pore-water profiles indicated the occurrence of sulfate depleting processes accompanied with carbonate precipitation. The pore-water profiles display evidence of biogeochemical transformations leading to the fast depletion of seawater sulfate within the first 25-cm depth of the sediment. These results show that the North Anatolian Fault and inherited faults are important migration paths for fluids for which a significant part is discharged into the water column, contributing to the increase of methane concentration at the bottom seawater and favoring the development of specific ecosystems.

Sitting at ∼5,000 m water depth on the Congo-Angola margin and ∼760 km offshore of the West African coast, the recent lobe complex of the Congo deep-sea fan receives large amounts of fluvial sediments (3–5% organic carbon). This organic-rich sedimentation area harbors habitats with chemosynthetic communities similar to those of cold seeps. In this study, we investigated relative abundance, diversity and distribution of aerobic methane-oxidizing bacteria (MOB) communities at the oxic–anoxic interface of sedimentary habitats by using fluorescence in situ hybridization and comparative sequence analysis of particulate mono-oxygenase (pmoA) genes. Our findings revealed that sedimentary habitats of the recent lobe complex hosted type I and type II MOB cells and comparisons of pmoA community compositions showed variations among the different organic-rich habitats. Furthermore, the pmoA lineages were taxonomically more diverse compared to methane seep environments and were related to those found at cold seeps. Surprisingly, MOB phylogenetic lineages typical of terrestrial environments were observed at such water depth. In contrast, MOB cells or pmoA sequences were not detected at the previous lobe complex that is disconnected from the Congo River inputs.

In the Guaymas Basin, the presence at a few tens of kilometers of cold seeps and hydrothermal vents coupled with comparable sedimentary settings and depths offer a unique opportunity to assess and compare the microbial community composition of these deep-sea ecosystems. The microbial diversity in sediments from three cold seep and two hydrothermal vent assemblages were investigated using high-throughput 16S rRNA-sequencing. Numerous bacterial and archaeal lineages were detected in both cold seep and hydrothermal vent sediments. Various potential organic matter degraders (e.g., Chloroflexi, Atribacteria, MBG-D) and methane and sulfur cycling related microorganisms (e.g., ANME and methanogenic lineages, sulfate-reducing lineages) were detected in both ecosystems. This suggests that analogous metabolic processes such as organic matter degradation and anaerobic methane oxidation coupled to sulfate reduction, were probably occurring in these two contrasted ecosystems. These highlighted “core microbiome” of the Guaymas Basin chemosynthetic ecosystems might therefore result from the combined presence of up-rising fluid emissions and high sedimentary rates of organic matter in the Basin. These results, coupled with the detailed ribotype analysis of major archaeal lineages (ANME-1, ANME-2, and MBG-D), also suggest a potential connectivity among deep-sea ecosystems of the Guaymas Basin likely due to the sedimentary context and the absence of physical border. However, thermophilic and hyperthermophilic lineages (e.g., Thermodesulfobacteria, Desulfurococcales, etc.) were exclusively identified in hydrothermally impacted sediments highlighting the strong influence of temperature gradients and other hydrothermally-related factors such as thermogenic sulfate reduction and sulfide formation on microbial community composition.

A novel hyperthermophilic, piezophilic, anaerobic archaeon, designated NCB100T, was isolated from a hydrothermal vent flange fragment collected in the Guaymas basin at the hydrothermal vent site named 'Rebecca's Roost' at a depth of 1997 m. Enrichment and isolation were performed at 100 °C under atmospheric pressure. Cells of strain NCB100T were highly motile, irregular cocci with a diameter of ~1 µm. Growth was recorded at temperatures between 70 and 112 °C (optimum 105 °C) and hydrostatic pressures of 0.1-80 MPa (optimum 40-50 MPa). Growth was observed at pH 3.5-8.5 (optimum pH 7) and with 1.5-7 % NaCl (optimum at 2.5-3 %). Strain NCB100T was a strictly anaerobic chemo-organoheterotroph and grew on complex proteinaceous substrates such as yeast extract, peptone and tryptone, as well as on glycogen and starch. Elemental sulfur was required for growth and was reduced to hydrogen sulfide. The fermentation products from complex proteinaceous substrates were CO2 and H2. The G+C content of the genomic DNA was 41.3 %. Phylogenetic analysis of the 16S rRNA gene sequence revealed that strain NCB100T belongs to the genus Pyrococcus, showing 99 % similarity with the other described species of the genus Pyrococcus. On the basis of physiological characteristics, DNA G+C content, similarity level between ribosomal proteins and an average nucleotide identity value of 79 %, strain NCB100T represents a novel species for which the name Pyrococcus kukulkanii sp. nov. is proposed. The type strain is NCB100T (=DSM 101590T=Souchothèque de Bretagne BG1337T).

To explore the capability of basaltic glass to support the growth of chemosynthetic microorganisms, complementary in situ and in vitro colonization experiments were performed. Microbial colonizers containing synthetic tholeitic basaltic glasses, either enriched in reduced or oxidized iron, were deployed off-axis from the Mid Atlantic Ridge on surface sediments of the abyssal plain (35°N; 29°W). In situ microbial colonization was assessed by sequencing of the 16S rRNA gene and basaltic glass alteration was characterized using Scanning Electron Microscopy, micro-X-ray Absorption Near Edge Structure at the Fe-K-edge and Raman microspectroscopy. The colonized surface of the reduced basaltic glass was covered by a rind of alteration made of iron-oxides trapped in a palagonite-like structure with thicknesses up to 150 μm. The relative abundance of the associated microbial community was dominated (39% of all reads) by a single operational taxonomic unit (OTU) that shared 92% identity with the iron-oxidizer Mariprofundus ferrooxydans PV-1. Conversely, the oxidized basaltic glass showed the absence of iron-oxides enriched surface deposits and correspondingly there was a lack of known iron-oxidizing bacteria in the inventoried diversity. In vitro, a similar reduced basaltic glass was incubated in artificial seawater with a pure culture of the iron-oxidizing M. ferrooxydans DIS-1 for 2 weeks, without any additional nutrients or minerals. Confocal Laser Scanning Microscopy revealed that the glass surface was covered by twisted stalks characteristic of this iron-oxidizing Zetaproteobacteria. This result supported findings of the in situ experiments indicating that the Fe(II) present in the basalt was the energy source for the growth of representatives of Zetaproteobacteria in both the abyssal plain and the in vitro experiment. In accordance, the surface alteration rind observed on the reduced basaltic glass incubated in situ could at least partly result from their activity.

The Sonora Margin cold seeps present a seafloor mosaic pattern consisting of different faunal assemblages and microbial mats. To better understand if sedimentary microbial communities reflect this patchy distribution, all major habitats were investigated using four complementary approaches: 16S rRNA 454 pyrosequencing, quantitative polymerase chain reaction, fluorescence in situ hybridization and geochemistry analyses. This study reveals that sediments populated by different surface assemblages show distinct porewater geochemistry features and are associated with distinct microbial communities. In the sediments underlying the microbial mat and the surrounding macrofauna, microbial communities were dominated by anaerobic methane oxidizers (archaeal anaerobic methanotroph ANME) and sulfate-reducing Deltaproteobacteria. In contrast, sediment-associated microbial communities underlying the megafauna habitats (vesicomyids and siboglinids) were characterized by a lower biomass and important proportions of the Marine Benthic Group D (MBG-D), Chloroflexi as well as filamentous Gammaproteobacteria and Deltaproteobacteria. Together, geochemical and microbial surveys indicate that porewater methane concentrations play an important role in the microbial community structure and subsequently in the establishment of the surface colonizers. Furthermore, presence and activity of the surface colonizers influence the underlying microbial communities probably because of modification of energy source availabilities.

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Active hydrothermal chimneys host diverse microbial communities exhibiting various metabolisms including those involved in various biogeochemical cycles. To investigate microbe–mineral–fluid interactions in hydrothermal chimney and the driver of microbial diversity, a cultural approach using a gas-lift bioreactor was chosen. An enrichment culture was performed using crushed active chimney sample as inoculum and diluted hydrothermal fluid from the same vent as culture medium. Daily sampling provided time-series access to active microbial diversity and medium composition. Active archaeal and bacterial communities consisted mainly of sulfur, sulfate and iron reducers and hydrogen oxidizers with the detection of Thermococcus, Archaeoglobus, Geoglobus, Sulfurimonas and Thermotoga sequences. The simultaneous presence of active Geoglobus sp. and Archaeoglobus sp. argues against competition for available carbon sources and electron donors between sulfate and iron reducers at high temperature. This approach allowed the cultivation of microbial populations that were under-represented in the initial environmental sample. The microbial communities are heterogeneously distributed within the gas-lift bioreactor; it is unlikely that bulk mineralogy or fluid chemistry is the drivers of microbial community structure. Instead, we propose that micro-environmental niche characteristics, created by the interaction between the mineral grains and the fluid chemistry, are the main drivers of microbial diversity in natural systems.

To assess the production and the export of particulate and biological material in deep-sea hydrothermal vents, four moorings with sediment traps and current meters were deployed for 24 days in the Azores Triple Junction (ATJ) region. They were deployed along an axis starting at the base of a hydrothermal vent chimney and ending 1000 m away. The particles sampled at the base of the chimney were characterized by high concentrations in total sulfur (16%) and iron (4%). The particle composition changed drastically with distance from the vent: the sulfur concentration decreased with an increase in clay components. Thermophilic microorganisms were successfully enriched from all the particle samples. Cultured strains were closely related to hydrothermal species, suggesting that viable hydrothermal vent microorganisms can be exported easily from one hydrothermal field to the open ocean. Fauna collected in the trap at the base of the chimney also included the hydrothermal mytilid species Bathymodiolus azoricus (prejuvenile prodissoconch late stage), larval or juvenile polychaetes and two vent gastropod species (Shinkailepas sp. and Phymorhynchus sp.). These organisms were not sampled by the others sediment traps. The most common taxa found in the traps off the vent were polychaetes, euphausiaceans and copepods (harpacticoids, nauplii and calanoids).

Oceanic basalts host diverse microbial communities with various metabolisms involved in C, N, S, and Fe biogeochemical cycles which may contribute to mineral and glass alteration processes at, and below the seafloor. In order to study the microbial colonization on basaltic glasses and their potential biotic/abiotic weathering products, two colonization modules called AISICS ("Autonomous in situ Instrumented Colonization System") were deployed in hydrothermal deep-sea sediments at the Guaymas Basin for 8 days and 22 days. Each AISICS module contained 18 colonizers (including sterile controls) filled with basaltic glasses of contrasting composition. Chemical analyses of ambient fluids sampled through the colonizers showed a greater contribution of hydrothermal fluids (maximum temperature 57.6°C) for the module deployed during the longer time period. For each colonizer, the phylogenetic diversity and metabolic function of bacterial and archaeal communities were explored using a molecular approach by cloning and sequencing. Results showed large microbial diversity in all colonizers. The bacterial distribution was primarily linked to the deployment duration, as well as the depth for the short deployment time module. Some 16s rRNA sequences formed a new cluster of Epsilonproteobacteria. Within the Archaea the retrieved diversity could not be linked to either duration, depth or substrata. However, mcrA gene sequences belonging to the ANME-1 mcrA-guaymas cluster were found sometimes associated with their putative sulfate-reducers syntrophs depending on the colonizers. Although no specific glass alteration texture was identified, nano-crystals of barite and pyrite were observed in close association with organic matter, suggesting a possible biological mediation. This study gives new insights into the colonization steps of volcanic rock substrates and the capability of microbial communities to exploit new environmental conditions.

A novel aerobic, gram-negative bacterial strain, designated 17X/A02/237(T), was isolated from waters of the coastal north-western Mediterranean Sea. Cells were motile straight rods and formed dark-grey colonies on marine agar medium. Strain 17X/A02/237(T) contained ubiquinone Q-8 and its major fatty acids were C(16 : 1)ω7c and/or iso-C(15 : 0) 2-OH, C(18 : 1)ω7c, C(16 : 0), C(18 : 0) and C(10 : 0) 3-OH. The G+C content of the genomic DNA was 47.5 mol%. Phylogenetic analysis of the 16S rRNA gene sequence placed the strain in the class Gammaproteobacteria. Based on 16S rRNA gene sequence data, as well as physiological and biochemical characteristics, this isolate represents a novel species of a new genus, for which the name of Eionea nigra gen. nov., sp. nov. is proposed. The type strain is 17X/A02/237(T) ( = DSM 19752(T) = CIP 109759(T) = MOLA 288(T)).

Diversity and function in microbial mats from the Lucky Strike hydrothermal vent field (Mid-Atlantic Ridge) were investigated using molecular approaches. DNA and RNA were extracted from mat samples overlaying hydrothermal deposits and Bathymodiolus azoricus mussel assemblages. We constructed and analyzed libraries of 16S rRNA gene sequences and sequences of functional genes involved in autotrophic carbon fixation [forms I and II RuBisCO (cbbL/M), ATP-citrate lyase B (aclB)]; methane oxidation [particulate methane monooxygenase (pmoA)] and sulfur oxidation [adenosine-5'-phosphosulfate reductase (aprA) and soxB]. To gain new insights into the relationships between mats and mussels, we also used new domain-specific 16S rRNA gene primers targeting Bathymodiolus sp. symbionts. All identified archaeal sequences were affiliated with a single group: the marine group 1 Thaumarchaeota. In contrast, analyses of bacterial sequences revealed much higher diversity, although two phyla Proteobacteria and Bacteroidetes were largely dominant. The 16S rRNA gene sequence library revealed that species affiliated to Beggiatoa Gammaproteobacteria were the dominant active population. Analyses of DNA and RNA functional gene libraries revealed a diverse and active chemolithoautotrophic population. Most of these sequences were affiliated with Gammaproteobacteria, including hydrothermal fauna symbionts, Thiotrichales and Methylococcales. PCR and reverse transcription-PCR using 16S rRNA gene primers targeted to Bathymodiolus sp. symbionts revealed sequences affiliated with both methanotrophic and thiotrophic endosymbionts.

A novel, strictly anaerobic, thermophilic, sulfate-reducing bacterium, designated strain AT1325(T), was isolated from a deep-sea hydrothermal vent at the Rainbow site on the Mid-Atlantic Ridge. This strain was subjected to a polyphasic taxonomic analysis. Cells were Gram-negative motile rods (approximately 2.4 x 0.6 microm) with a single polar flagellum. Strain AT1325(T) grew at 55-75 degrees C (optimum, 65-70 degrees C), at pH 5.5-8.0 (optimum, 6.5-7.5) and in the presence of 1.5-4.5 % (w/v) NaCl (optimum, 2.5 %). Cells grew chemolithoautotrophically with H2 as an energy source and SO4(2-) as an electron acceptor. Alternatively, the novel isolate was able to use methylamine, peptone or yeast extract as carbon sources. The dominant fatty acids (>5 % of the total) were C(16 : 0), C(18 : 1)omega7c, C(18 : 0) and C(19 : 0) cyclo omega8c. The G+C content of the genomic DNA of strain AT1325(T) was 45.6 mol%. Phylogenetic analyses based on 16S rRNA gene sequences placed strain AT1325(T) within the family Thermodesulfobacteriaceae, in the bacterial domain. Comparative 16S rRNA gene sequence analysis indicated that strain AT1325(T) belonged to the genus Thermodesulfatator, sharing 97.8 % similarity with the type strain of Thermodesulfatator indicus, the unique representative species of this genus. On the basis of the data presented, it is suggested that strain AT1325(T) represents a novel species of the genus Thermodesulfatator, for which the name Thermodesulfatator atlanticus sp. nov. is proposed. The type strain is AT1325(T) (=DSM 21156(T)=JCM 15391(T)).

A novel Gram-negative bacteria, named CZ41_10a(T), was isolated from coastal surface waters of the north-western Mediterranean Sea. Cells were motile, pleomorphic rods, 1.6 mum long and 0.7 mum wide and formed cream colonies on marine agar medium. The G+C content of the genomic DNA was 65 mol%. Phylogenetic analysis of 16S rRNA gene sequences placed the new isolate in the genus Thalassobaculum, a member of the family Rhodospirillaceae, class Alphaproteobacteria. Unlike Thalassobaculum litoreum CL-GR58(T), its closest relative, strain CZ41_10a(T) was unable to grow anaerobically and did not exhibit nitrate reductase activity. On the basis of DNA-DNA hybridization, fatty acid content and physiological and biochemical characteristics, this isolate represents a novel species for which the name Thalassobaculum salexigens sp. nov. is proposed. The type strain is CZ41_10a(T) (=DSM 19539(T)=CIP 109604(T)=MOLA [corrected] 84(T)). An emended description of the genus Thalassobaculum is also given.