Niche partitioning of diverse sulfur-oxidizing bacteria at hydrothermal vents.

At deep-sea hydrothermal vents, primary production is carried out by chemolithoautotrophic microorganisms, with the oxidation of reduced sulfur compounds being a major driver for microbial carbon fixation. Dense and highly diverse assemblies of sulfur-oxidizing bacteria (SOB) are observed, yet the principles of niche differentiation between the different SOB across geochemical gradients remain poorly understood. In this study niche differentiation of the key SOB was addressed by extensive sampling of active sulfidic vents at six different hydrothermal venting sites in the Manus Basin, off Papua New Guinea. We subjected 33 diffuse fluid and water column samples and 23 samples from surfaces of chimneys, rocks and fauna to a combined analysis of 16S rRNA gene sequences, metagenomes and real-time in situ measured geochemical parameters. We found Sulfurovum Epsilonproteobacteria mainly attached to surfaces exposed to diffuse venting, while the SUP05-clade dominated the bacterioplankton in highly diluted mixtures of vent fluids and seawater. We propose that the high diversity within Sulfurimonas- and Sulfurovum-related Epsilonproteobacteria observed in this study derives from the high variation of environmental parameters such as oxygen and sulfide concentrations across small spatial and temporal scales.

Motility in the epsilon-proteobacteria.

The epsilon-proteobacteria are a widespread group of flagellated bacteria frequently associated with either animal digestive tracts or hydrothermal vents, with well-studied examples in the human pathogens of Helicobacter and Campylobacter genera. Flagellated motility is important to both pathogens and hydrothermal vent members, and a number of curious differences between the epsilon-proteobacterial and enteric bacterial motility paradigms make them worthy of further study. The epsilon-proteobacteria have evolved to swim at high speed and through viscous media that immobilize enterics, a phenotype that may be accounted for by the molecular architecture of the unusually large epsilon-proteobacterial flagellar motor. This review summarizes what is known about epsilon-proteobacterial motility and focuses on a number of recent discoveries that rationalize the differences with enteric flagellar motility.

Functional interactions among filamentous Epsilonproteobacteria and Bacteroidetes in a deep-sea hydrothermal vent biofilm.

Little is known about how lithoautotrophic primary production is connected to microbial organotrophic consumption in hydrothermal systems. Using a multifaceted approach, we analysed the structure and metabolic capabilities within a biofilm growing on the surface of a black smoker chimney in the Loki's Castle vent field. Imaging revealed the presence of rod-shaped Bacteroidetes growing as ectobionts on long, sheathed microbial filaments (> 100 µm) affiliated with the Sulfurovum genus within Epsilonproteobacteria. The filaments were composed of a thick (> 200 nm) stable polysaccharide, representing a substantial fraction of organic carbon produced by primary production. An integrated -omics approach enabled us to assess the metabolic potential and in situ metabolism of individual taxonomic and morphological groups identified by imaging. Specifically, we provide evidence that organotrophic Bacteroidetes attach to and glide along the surface of Sulfurovum filaments utilizing organic polymers produced by the lithoautotrophic Sulfurovum. Furthermore, in situ expression of acetyl-CoA synthetase by Sulfurovum suggested the ability to assimilate acetate, indicating recycling of organic matter in the biofilm. This study expands our understanding of the lifestyles of Epsilonproteobacteria in hydrothermal vents, their metabolic properties and co-operative interactions in deep-sea hydrothermal vent food webs.

Nitrogenase expression in estuarine bacterioplankton influenced by organic carbon and availability of oxygen.

The genetic capacity to fix gaseous nitrogen (N) is distributed among diverse diazotrophs belonging to the Bacteria and Archaea. However, only a subset of the putative diazotrophs present actively fix N at any given time in the environment. We experimentally tested whether the availability of carbon and inhibition by oxygen constrain N fixation by diazotrophs in coastal seawater. The goal was to test whether by alleviating these constraints an increased overlap between nitrogenase (nifH)-gene-carrying and -expressing organisms could be achieved. We incubated water from a eutrophic but N-limited fjord in Denmark under high-carbon/low-oxygen conditions and determined bacterial growth and production, diazotrophic community composition (Illumina nifH amplicon sequencing), and nifH gene abundance and expression [quantitative PCR (qPCR) and quantitative reverse transcriptase PCR (qRT-PCR)]. Bacterial abundances and production increased under high-carbon/low-oxygen conditions as did the similarity between present and active diazotrophic communities. This was caused by the loss of specific abundant yet non-active gammaproteobacterial phylotypes and increased expression by others. The prominent active gamma- and epsilonproteobacterial diazotrophs did not, however, respond to these conditions in a uniform way, highlighting the difficulty to assess how a change in environmental conditions may affect a diverse indigenous diazotrophic community.

Fast-moving bacteria self-organize into active two-dimensional crystals of rotating cells.

We investigate a new form of collective dynamics displayed by Thiovulum majus, one of the fastest-swimming bacteria known. Cells spontaneously organize on a surface into a visually striking two-dimensional hexagonal lattice of rotating cells. As each constituent cell rotates its flagella, it creates a tornadolike flow that pulls neighboring cells towards and around it. As cells rotate against their neighbors, they exert forces on one another, causing the crystal to rotate and cells to reorganize. We show how these dynamics arise from hydrodynamic and steric interactions between cells. We derive the equations of motion for a crystal, show that this model explains several aspects of the observed dynamics, and discuss the stability of these active crystals.

Hydrodynamics and collective behavior of the tethered bacterium Thiovulum majus.

The ecology and dynamics of many microbial systems, particularly in mats and soils, are shaped by how bacteria respond to evolving nutrient gradients and microenvironments. Here we show how the response of the sulfur-oxidizing bacterium Thiovulum majus to changing oxygen gradients causes cells to organize into large-scale fronts. To study this phenomenon, we develop a technique to isolate and enrich these bacteria from the environment. Using this enrichment culture, we observe the formation and dynamics of T. majus fronts in oxygen gradients. We show that these dynamics can be understood as occurring in two steps. First, chemotactic cells moving up the oxygen gradient form a front that propagates with constant velocity. We then show, through observation and mathematical analysis, that this front becomes unstable to changes in cell density. Random perturbations in cell density create oxygen gradients. The response of cells magnifies these gradients and leads to the formation of millimeter-scale fluid flows that actively pull oxygenated water through the front. We argue that this flow results from a nonlinear instability excited by stochastic fluctuations in the density of cells. Finally, we show that the dynamics by which these modes interact can be understood from the chemotactic response of cells. These results provide a mathematically tractable example of how collective phenomena in ecological systems can arise from the individual response of cells to a shared resource.

The versatile in situ gene expression of an Epsilonproteobacteria-dominated biofilm from a hydrothermal chimney.

The Epsilonproteobacteria, including members of the genus Sulfurovum, are regarded as important primary producers in hydrothermal systems. However, their in situ gene expression in this habitat has so far not been investigated. We report a metatranscriptomic analysis of a Sulfurovum-dominated biofilm from one of the chimneys at the Loki's Castle hydrothermal system, located at the Arctic Mid Ocean Ridge. Transcripts involved in hydrogen oxidation, oxidation of sulfur species, aerobic respiration and denitrification were abundant and mostly assigned to Sulfurovum, indicating that members of this genus utilize multiple chemical energy sources simultaneously for primary production. Sulfurovum also seemed to have a diverse expression of transposases, potentially involved in horizontal gene transfer. Other transcripts were involved in CO2 fixation by the reverse TCA cycle, the CRISPR-Cas system, heavy metal resistance, and sensing and responding to changing environmental conditions. Through pyrosequencing of PCR amplified 16S rRNA genes, the Sulfurovum-dominated biofilm was compared with another biofilm from the same chimney, revealing a large shift in the community structure of Epsilonproteobacteria-dominated biofilms over a few metres.

Bacterial community composition in a large marine anoxic basin: a Cariaco Basin time-series survey.

Redox transition zones play a crucial role in biogeochemical cycles of several major elements. Because microorganisms mediate many reactions of these cycles, they actively participate in establishing geochemical gradients. In turn, the geochemical gradients structure microbial communities. We studied the interrelationship between the bacterial community structure and the geochemical gradient in the Cariaco Basin, the largest truly marine anoxic basin. This study's dataset includes bacterial community composition in 113 water column samples as well as the data for environmental variables (gradients of oxygen, hydrogen sulfide, sulfite, thiosulfate, ammonia, nitrate, nitrite, dissolved manganese and iron, dark CO2 fixation, and bacterial abundance) collected between 1997 and 2006. Several prominent bacterial groups are present throughout the entire water column. These include members of Gamma-, Delta-, and Epsilonproteobacteria, as well as members of the Marine Group A, the candidate divisions OP11 and Car731c. Canonical correspondence analysis indicated that microbial communities segregate along vectors representing oxygenated conditions, nitrite, nitrate and anoxic environments represented by chemoautotrophy, ammonia, sulfite, and hydrogen sulfide.

Impact of protist grazing on a key bacterial group for biogeochemical cycling in Baltic Sea pelagic oxic/anoxic interfaces.

Barrier zones between oxic and anoxic water masses (redoxclines) host highly active prokaryotic communities with important roles in biogeochemical cycling. In Baltic Sea pelagic redoxclines, Epsilonproteobacteria of the genus Sulfurimonas (subgroup GD17) have been shown to dominate chemoautotrophic denitrification. However, little is known on the loss processes affecting this prokaryotic group. In the present study, the protist grazing impact on the Sulfurimonas subgroup GD17 was determined for suboxic and oxygen/hydrogen sulphide interface depths of Baltic Sea redoxclines, using predator exclusion assays and bacterial amendment with the cultured representative 'Sulfurimonas gotlandica' strain GD1. Additionally, the principal bacterivores were identified by RNA-Stable Isotope Probing (RNA-SIP). The natural Sulfurimonas subgroup GD17 population grew strongly under oxygen/hydrogen sulphide interface conditions (doubling time: 1-1.5 days), but protist grazing could consume the complete new cell production per day. In suboxic samples, little or no growth of Sulfurimonas subgroup GD17 was observed. RNA-SIP identified five active grazers, belonging to typical redoxcline ciliates (Oligohymenophorea, Prostomatea) and globally widespread marine flagellate groups (MAST-4, Chrysophyta, Cercozoa). Overall, we demonstrate for the first time that protist grazing can control the growth, and potentially the vertical distribution, of a chemolithoautotrophic key-player of oxic/anoxic interfaces.

Inorganic carbon fixation by chemosynthetic ectosymbionts and nutritional transfers to the hydrothermal vent host-shrimp Rimicaris exoculata.

The shrimp Rimicaris exoculata dominates several hydrothermal vent ecosystems of the Mid-Atlantic Ridge and is thought to be a primary consumer harbouring a chemoautotrophic bacterial community in its gill chamber. The aim of the present study was to test current hypotheses concerning the epibiont's chemoautotrophy, and the mutualistic character of this association. In-vivo experiments were carried out in a pressurised aquarium with isotope-labelled inorganic carbon (NaH(13)CO(3) and NaH(14)CO(3)) in the presence of two different electron donors (Na(2)S(2)O(3) and Fe(2+)) and with radiolabelled organic compounds ((14)C-acetate and (3)H-lysine) chosen as potential bacterial substrates and/or metabolic by-products in experiments mimicking transfer of small biomolecules from epibionts to host. The bacterial epibionts were found to assimilate inorganic carbon by chemoautotrophy, but many of them (thick filaments of epsilonproteobacteria) appeared versatile and able to switch between electron donors, including organic compounds (heterotrophic acetate and lysine uptake). At least some of them (thin filamentous gammaproteobacteria) also seem capable of internal energy storage that could supply chemosynthetic metabolism for hours under conditions of electron donor deprivation. As direct nutritional transfer from bacteria to host was detected, the association appears as true mutualism. Import of soluble bacterial products occurs by permeation across the gill chamber integument, rather than via the digestive tract. This first demonstration of such capabilities in a decapod crustacean supports the previously discarded hypothesis of transtegumental absorption of dissolved organic matter or carbon as a common nutritional pathway.

Cell-specific thioautotrophic productivity of epsilon-proteobacterial epibionts associated with Shinkaia crosnieri.

In this study, we report experimental evidence of the thioautotrophic activity of the epibiotic microbial community associated with the setae of Shinkaia crosnieri, a galatheid crab that is endemic to deep-sea hydrothermal systems in the Okinawa Trough in Japan. Microbial consumption of reduced sulfur compounds under in situ hydrostatic and atmospheric pressure provided evidence of sulfur-oxidizing activity by the epibiotic microbial community; the rate of sulfur oxidation was similar under in situ and decompressed conditions. Results of the microbial consumption of reduced sulfur compounds and tracer experiments using (13)C-labeled bicarbonate in the presence and absence of thiosulfate (used as a thioautotrophic substrate) convincingly demonstrated that the epibiotic microbial community on S. crosnieri drove primary production via an energy metabolism that was coupled with the oxidation of reductive sulfur compounds. A combination of tracer experiments, fluorescence in situ hybridization (FISH) and nano-scale secondary ion mass spectrometry (Nano-SIMS) indicated that the filamentous cells of the genus Sulfurovum belonging to the class Epsilonproteobacteria were thioautotrophs in the epibiotic community of S. crosnieri. In conclusion, our results strongly suggest that thioautotrophic production by Sulfurovum members present as the epibiotic microbial community play a predominant role in a probable nutritional ectosymbiosis with S. crosnieri.

Thiofractor thiocaminus gen. nov., sp. nov., a novel hydrogen-oxidizing, sulfur-reducing epsilonproteobacterium isolated from a deep-sea hydrothermal vent chimney in the Nikko Seamount field of the northern Mariana Arc.

A novel chemolithoautotrophic hydrogen-oxidizing and sulfur-reducing bacterium, strain 496Chim(T), was isolated from a deep-sea hydrothermal vent chimney collected from the hydrothermal field at the summit of Nikko Seamount field, in the Mariana Arc. Cells were rods or curved rods, motile by means of a single polar flagellum. Growth was observed between 15 and 45 °C (optimum 37 °C; doubling time, 2.1 h) and between pH 5.3 and 8.0 (optimum pH 6.0). The isolate was a strictly anaerobic, obligate chemolithoautotroph capable of growth using molecular hydrogen as the sole energy source, carbon dioxide as the sole carbon source, ammonium or nitrate as the sole nitrogen source, and elemental sulfur as the electron acceptor. The G+C content of genomic DNA was 35 mol%. Phylogenetic analysis based on 16S rRNA gene sequences indicated that the new isolate belonged to the class Epsilonproteobacteria, but the isolate was distantly related to the previously described Epsilonproteobacteria species potentially at the genus level (<90 %). On the basis of its physiological and molecular characteristics, strain 496Chim(T) (=DSM 22050(Τ) = JCM 15747(Τ) = NBRC 105224(Τ)) represents the sole species of a new genus, Thiofractor, for which the name Thiofractor thiocaminus is proposed.

Acquisition of epibiotic bacteria along the life cycle of the hydrothermal shrimp Rimicaris exoculata.

The caridean shrimp Rimicaris exoculata dominates the fauna at several Mid-Atlantic Ridge hydrothermal vent sites. This shrimp has an enlarged gill chamber, harboring a dense ectosymbiotic community of chemoautotrophic bacteria associated with mineral oxide deposits. Until now, their acquisition is not fully understood. At three hydrothermal vent sites, we analyzed the epibionts diversity at different moult stages and also in the first stages of the shrimp life (eggs, hatched eggs (with larvae) and juveniles). Hatched eggs associated with young larvae were collected for the first time directly from gravid females at the Logachev vent site during the Serpentine cruise. An approach using 16S rRNA clone libraries, scanning and transmission electron microscopy, and fluorescent in situ hybridization was used. Molecular results and microscope observations indicated a switch in the composition of the bacterial community between early R. exoculata life cycle stage (egg libraries dominated by the Gammaproteobacteria) and later stages (juvenile/adult libraries dominated by the Epsilonproteobacteria). We hypothesized that the epibiotic phylotype composition could vary according to the life stage of the shrimp. Our results confirmed the occurrence of a symbiosis with Gammaproteobacteria and Epsilonproteobacteria, but more complex than previously assumed. We revealed the presence of active type-I methanotrophic bacteria colonizing the cephalothorax of shrimps from the Rainbow site. They were also present on the eggs from the Logachev site. This could be the first 'epibiotic' association between methanotrophic bacteria and hydrothermal vent crustacean. We discuss possible transmission pathways for epibionts linked to the shrimp life cycle.

Drivers of epsilonproteobacterial community composition in sulfidic caves and springs.

Epsilonproteobacteria are widely distributed in marine, freshwater, and terrestrial environments, although most well-studied groups are from hydrothermal vents and the human intestinal tract. The environmental variables that control epsilonproteobacterial communities in sulfidic terrestrial environments, however, are poorly understood. Here, the environmental variables that influence epsilonproteobacterial community composition in geographically separated sulfidic caves and springs were determined by coarse and fine-scale approaches: denaturing gradient gel electrophoresis profiling of 23S rRNA PCR amplicons and clone library sequencing of the 16S-ITS-23S rRNA operon. Sequences retrieved from this study were not closely related to cultured representatives, indicating that existing culture collections do not adequately capture the diversity of terrestrial Epsilonproteobacteria. Comparisons of 16S-ITS-23S rRNA operon sequences from four sites revealed that some distant communities (> 8000 km) share closely related populations of Epsilonproteobacteria, while other sites have nearly clonal and phylogenetically distinct populations. Statistical evaluations of sequence data reveal that multiple environmental variables (e.g. temperature, pH, salinity, dissolved oxygen, and bicarbonate concentrations) influence Epsilonproteobacteria community composition. Locations with clonal populations tended to be from higher temperatures and intermediate dissolved oxygen concentrations. rRNA operon sequences outside of the 16S rRNA gene may be critical to recognizing environmental drivers of epsilonproteobacterial community composition.

A gastric pathogen moves chemotaxis in a new direction.

For almost 50 years, Escherichia coli has been the model for understanding how bacteria orient their movement in response to chemical cues, but recent studies of chemotaxis in other bacteria have revealed interesting variations from prevailing paradigms. Investigating the human pathogen Helicobacter pylori, Amieva and colleagues [mBio 2(4):e00098-11, 2011] discovered a new chemotaxis regulator, ChePep, which modulates swimming behavior through the canonical histidine-aspartate phosphorelay system. Functionally conserved among the epsilonproteobacteria, ChePep is essential for H. pylori to navigate deep into the stomach's gastric glands and may be an attractive target for novel antibiotics.

ChePep controls Helicobacter pylori Infection of the gastric glands and chemotaxis in the Epsilonproteobacteria.

UNLABELLED: Microbes use directed motility to colonize harsh and dynamic environments. We discovered that Helicobacter pylori strains establish bacterial colonies deep in the gastric glands and identified a novel protein, ChePep, necessary to colonize this niche. ChePep is preferentially localized to the flagellar pole. Although mutants lacking ChePep have normal flagellar ultrastructure and are motile, they have a slight defect in swarming ability. By tracking the movement of single bacteria, we found that ΔChePep mutants cannot control the rotation of their flagella and swim with abnormally frequent reversals. These mutants even sustain bursts of movement backwards with the flagella pulling the bacteria. Genetic analysis of the chemotaxis signaling pathway shows that ChePep regulates flagellar rotation through the chemotaxis system. By examining H. pylori within a microscopic pH gradient, we determined that ChePep is critical for regulating chemotactic behavior. The chePep gene is unique to the Epsilonproteobacteria but is found throughout this diverse group. We expressed ChePep from other members of the Epsilonproteobacteria, including the zoonotic pathogen Campylobacter jejuni and the deep sea hydrothermal vent inhabitant Caminibacter mediatlanticus, in H. pylori and found that ChePep is functionally conserved across this class. ChePep represents a new family of chemotaxis regulators unique to the Epsilonproteobacteria and illustrates the different strategies that microbes have evolved to control motility. IMPORTANCE: Helicobacter pylori strains infect half of all humans worldwide and contribute to the development of peptic ulcers and gastric cancer. H. pylori cannot survive within the acidic lumen of the stomach and uses flagella to actively swim to and colonize the protective mucus and epithelium. The chemotaxis system allows H. pylori to navigate by regulating the rotation of its flagella. We identified a new protein, ChePep, which controls chemotaxis in H. pylori. ChePep mutants fail to colonize the gastric glands of mice and are completely outcompeted by normal H. pylori. Genes encoding ChePep are found only in the class Epsilonproteobacteria, which includes the human pathogen Campylobacter jejuni and environmental microbes like the deep-sea hydrothermal vent colonizer Caminibacter mediatlanticus, and we show that ChePep function is conserved in this class. Our study identifies a new colonization factor in H. pylori and also provides insight into the control and evolution of bacterial chemotaxis.

Identity of epibiotic bacteria on symbiontid euglenozoans in O2-depleted marine sediments: evidence for symbiont and host co-evolution.

A distinct subgroup of euglenozoans, referred to as the 'Symbiontida,' has been described from oxygen-depleted and sulfidic marine environments. By definition, all members of this group carry epibionts that are intimately associated with underlying mitochondrion-derived organelles beneath the surface of the hosts. We have used molecular phylogenetic and ultrastructural evidence to identify the rod-shaped epibionts of the two members of this group, Calkinsia aureus and B.bacati, hand-picked from the sediments of two separate oxygen-depleted, sulfidic environments. We identify their epibionts as closely related sulfur or sulfide-oxidizing members of the epsilon proteobacteria. The epsilon proteobacteria generally have a significant role in deep-sea habitats as primary colonizers, primary producers and/or in symbiotic associations. The epibionts likely fulfill a role in detoxifying the immediate surrounding environment for these two different hosts. The nearly identical rod-shaped epibionts on these two symbiontid hosts provides evidence for a co-evolutionary history between these two sets of partners. This hypothesis is supported by congruent tree topologies inferred from 18S and 16S rDNA from the hosts and bacterial epibionts, respectively. The eukaryotic hosts likely serve as a motile substrate that delivers the epibionts to the ideal locations with respect to the oxic/anoxic interface, whereby their growth rates can be maximized, perhaps also allowing the host to cultivate a food source. Because symbiontid isolates and additional small subunit rDNA gene sequences from this clade have now been recovered from many locations worldwide, the Symbiontida are likely more widespread and diverse than presently known.

Nautilia nitratireducens sp. nov., a thermophilic, anaerobic, chemosynthetic, nitrate-ammonifying bacterium isolated from a deep-sea hydrothermal vent.

A thermophilic, anaerobic, chemosynthetic bacterium, designated strain MB-1(T), was isolated from the walls of an active deep-sea hydrothermal vent chimney on the East Pacific Rise at degrees 50' N 10 degrees 17' W. The cells were Gram-negative-staining rods, approximately 1-1.5 mum long and 0.3-0.5 mum wide. Strain MB-1(T) grew at 25-65 degrees C (optimum 55 degrees C), with 10-35 g NaCl l(-1) (optimum 20 g l(-1)) and at pH 4.5-8.5 (optimum pH 7.0). Generation time under optimal conditions was 45.6 min. Growth occurred under chemolithoautotrophic conditions with H(2) as the energy source and CO(2) as the carbon source. Nitrate was used as the electron acceptor, with resulting production of ammonium. Thiosulfate, sulfur and selenate were also used as electron acceptors. No growth was observed in the presence of lactate, peptone or tryptone. Chemo-organotrophic growth occurred in the presence of acetate, formate, Casamino acids, sucrose, galactose and yeast extract under a N(2)/CO(2) gas phase. The G+C content of the genomic DNA was 36.0 mol%. Phylogenetic analysis of the 16S rRNA gene sequence indicated that this organism is closely related to Nautilia profundicola AmH(T), Nautilia abyssi PH1209(T) and Nautilia lithotrophica 525(T) (95, 94 and 93 % sequence identity, respectively). On the basis of phylogenetic, physiological and genetic considerations, it is proposed that the organism represents a novel species within the genus Nautilia, Nautilia nitratireducens sp. nov. The type strain is MB-1(T) (=DSM 22087(T) =JCM 15746(T)).

Nautilia abyssi sp. nov., a thermophilic, chemolithoautotrophic, sulfur-reducing bacterium isolated from an East Pacific Rise hydrothermal vent.

A novel strictly anaerobic, thermophilic, sulfur-reducing bacterium, designated PH1209(T), was isolated from an East Pacific Rise hydrothermal vent (1 degrees N) sample and studied using a polyphasic taxonomic approach. Cells were Gram-negative, motile rods (approx. 1.60 x 0.40 microm) with a single polar flagellum. Strain PH1209(T) grew at temperatures between 33 and 65 degrees C (optimum 60 degrees C), from pH 5.0 to 8.0 (optimum 6.0-6.5), and between 2 and 4 % (w/v) NaCl (optimum 3 %). Cells grew chemolithoautotrophically with H(2) as an energy source, S(0) as an electron acceptor and CO(2) as a carbon source. Strain PH1209(T) was also able to use peptone and yeast extract as carbon sources. The G+C content of the genomic DNA was 35 mol%. Phylogenetic analyses based on 16S rRNA gene sequencing showed that strain PH1209(T) fell within the order Nautiliales, in the class Epsilonproteobacteria. Comparative 16S rRNA gene sequence analysis indicated that strain PH1209(T) belonged to the genus Nautilia and shared 97.2 and 98.7 % 16S rRNA gene sequence identity, respectively, with the type strains of Nautilia lithotrophica and Nautilia profundicola. It is proposed, from the polyphasic evidence, that the strain represents a novel species, Nautilia abyssi sp. nov.; the type strain is PH1209(T) (=DSM 21157(T)=JCM 15390(T)).

Nautilia profundicola sp. nov., a thermophilic, sulfur-reducing epsilonproteobacterium from deep-sea hydrothermal vents.

A thermophilic, strictly anaerobic, sulfur-reducing epsilonproteobacterium (strain AmH(T)) isolated from deep-sea hydrothermal vents is described. Cells were motile, Gram-negative rods. Growth was observed at 30-55 degrees C, pH 6.0-9.0 and 2-5 % (w/v) NaCl. Chemolithoautotrophic growth occurred with molecular hydrogen or formate as the electron donor and elemental sulfur as the electron acceptor, producing hydrogen sulfide. Heterotrophic and mixotrophic growth occurred with formate as a source of carbon. The dominant phospholipid fatty acids were C(18 : 1)omega7c (73.26 % of the total), C(16 : 1)omega7c (12.70 %) and C(16 : 0) (12.27 %). The genomic DNA G+C content was 33.5 mol%. Phylogenetic analysis based on 16S rRNA gene sequences placed strain AmH(T) within the family Nautiliaceae of the Epsilonproteobacteria. DNA-DNA hybridization experiments between strain AmH(T) and Nautilia lithotrophica DSM 13520(T) revealed a level of relatedness of 34.6 % between the two strains. Based on physiological and phylogenetic characteristics, strain AmH(T) is considered to represent a novel species of the genus Nautilia, for which the name Nautilia profundicola sp. nov. is proposed. The type strain is AmH(T) (=ATCC BAA-1463(T) =DSM 18972(T)).