Microbial diversity of Loki's Castle black smokers at the Arctic Mid‐Ocean Ridge

Hydrothermal vent systems harbor rich microbial communities ranging from aerobic mesophiles to anaerobic hyperthermophiles. Among these, members of the archaeal domain are prevalent in microbial communities in the most extreme environments, partly because of their temperature‐resistant and robust membrane lipids. In this study, we use geochemical and molecular microbiological methods to investigate the microbial diversity in black smoker chimneys from the newly discovered Loki's Castle hydrothermal vent field on the Arctic Mid‐Ocean Ridge (AMOR) with vent fluid temperatures of 310–320 °C and pH of 5.5. Archaeal glycerol dialkyl glycerol tetraether lipids (GDGTs) and H‐shaped GDGTs with 0–4 cyclopentane moieties were dominant in all sulfide samples and are most likely derived from both (hyper)thermophilic Euryarchaeota and Crenarchaeota. Crenarchaeol has been detected in low abundances in samples derived from the chimney exterior indicating the presence of Thaumarchaeota at lower ambient temperatures. Aquificales and members of the Epsilonproteobacteria were the dominant bacterial groups detected. Our observations based on the analysis of 16S rRNA genes and biomarker lipid analysis provide insight into microbial communities thriving within the porous sulfide structures of active and inactive deep‐sea hydrothermal vents. Microbial cycling of sulfur, hydrogen, and methane by archaea in the chimney interior and bacteria in the chimney exterior may be the prevailing biogeochemical processes in this system.     

Ultrastructural evidence for iron accumulation within the tube of Vestimentiferan Ridgeia piscesae

This study reports on the accumulation of iron within the tube wall of the deep sea vent macro invertebrate Vestimentiferan Ridgeia piscesae collected from Juan de Fuca ridge. Combining an array of approaches including environmental scanning electron microscope (ESEM), electron probe micro-analysis (EPMA), X-ray microanalysis (EDS) and transmission electron microscope (TEM), we provide evidences for the influence of prokaryotic organisms on the accumulation of metals on and within the tube wall. Two types of iron-rich minerals such as iron oxides and framboidal pyrites are identified within or on the tube wall. Our results reveal the presence of prokaryotic organism is apparently responsible for the early accumulation of iron-rich minerals in the tube wall. The implications of the biomineralisation of iron in tube wall at hydrothermal vents are discussed.     

Anaerobic Respiration on Tellurate and Other Metalloids in Bacteria from Hydrothermal Vent Fields in the Eastern Pacific Ocean

This paper reports the discovery of anaerobic respiration on tellurate by bacteria isolated from deep ocean (1,543 to 1,791 m) hydrothermal vent worms. The first evidence for selenite- and vanadate-respiring bacteria from deep ocean hydrothermal vents is also presented. Enumeration of the anaerobic metal(loid)-resistant microbial community associated with hydrothermal vent animals indicates that a greater proportion of the bacterial community associated with certain vent fauna resists and reduces metal(loid)s anaerobically than aerobically, suggesting that anaerobic metal(loid) respiration might be an important process in bacteria that are symbiotic with vent fauna. Isolates from Axial Volcano and Explorer Ridge were tested for their ability to reduce tellurate, selenite, metavanadate, or orthovanadate in the absence of alternate electron acceptors. In the presence of metal(loid)s, strains showed an ability to grow and produce ATP, whereas in the absence of metal(loid)s, no growth or ATP production was observed. The protonophore carbonyl cyanide m-chlorophenylhydrazone depressed metal(loid) reduction. Anaerobic tellurate respiration will be a significant component in describing biogeochemical cycling of Te at hydrothermal vents.     

Anaerobic respiration on tellurate and other metalloids in bacteria from hydrothermal vent fields in the eastern Pacific Ocean

This paper reports the discovery of anaerobic respiration on tellurate by bacteria isolated from deep ocean (1,543 to 1,791 m) hydrothermal vent worms. The first evidence for selenite- and vanadate-respiring bacteria from deep ocean hydrothermal vents is also presented. Enumeration of the anaerobic metal(loid)-resistant microbial community associated with hydrothermal vent animals indicates that a greater proportion of the bacterial community associated with certain vent fauna resists and reduces metal(loid)s anaerobically than aerobically, suggesting that anaerobic metal(loid) respiration might be an important process in bacteria that are symbiotic with vent fauna. Isolates from Axial Volcano and Explorer Ridge were tested for their ability to reduce tellurate, selenite, metavanadate, or orthovanadate in the absence of alternate electron acceptors. In the presence of metal(loid)s, strains showed an ability to grow and produce ATP, whereas in the absence of metal(loid)s, no growth or ATP production was observed. The protonophore carbonyl cyanide m-chlorophenylhydrazone depressed metal(loid) reduction. Anaerobic tellurate respiration will be a significant component in describing biogeochemical cycling of Te at hydrothermal vents.     

Genetic diversity and connectivity of deep‐sea hydrothermal vent metapopulations

Deep‐sea hydrothermal vents provide ephemeral habitats for animal communities that depend on chemosynthetic primary production. Sporadic volcanic and tectonic events destroy local vent fields and create new ones. Ongoing dispersal and cycles of extirpation and colonization affect the levels and distribution of genetic diversity in vent metapopulations. Several species exhibit evidence for stepping‐stone dispersal along relatively linear, oceanic, ridge axes. Other species exhibit very high rates of gene flow, although natural barriers associated with variation in depth, deep‐ocean currents, and lateral offsets of ridge axes often subdivide populations. Various degrees of impedance to dispersal across such boundaries are products of species‐specific life histories and behaviours. Though unrelated to the size of a species range, levels of genetic diversity appear to correspond with the number of active vent localities that a species occupies within its range. Pioneer species that rapidly colonize nascent vents tend to be less subdivided and more diverse genetically than species that are slow to establish colonies at vents. Understanding the diversity and connectivity of vent metapopulations provides essential information for designing deep‐sea preserves in regions that are under consideration for submarine mining of precious metals.     

Haemocyte response associated with induction of shell regeneration in the deep-sea vent mussel Bathymodiolus azoricus (Bivalvia: Mytilidae)

This study reports on the haemocyte responses after induction of shell regeneration in the hydrothermal mussel Bathymodiolus azoricus. Haemolymph was drawn from live mussels collected at Menez Gwen hydrothermal vent site (850 m depth) at the Mid Atlantic Ridge (MAR) and was compared with those collected following laboratory acclimatisation (1 atm and Ca-rich algal diet) and also with induced specimen for up to 30 days. Simultaneously, histological changes in mantle micro-morphology with the histochemical detection of Ca mobilisation in tissues were conducted.On the basis of light- and transmission electron microscopy, it is concluded that the physiological equipment involved in shell regeneration in the deep sea bivalve closely resembles that in littoral mytilids, a group that B. azoricus is closely related. This in spite of previously alleged molecular and cellular adaptations to extreme conditions typical at deep sea hydrothermal vents. Three types of blood cells were identified sharing various morphological similarities with those in many non-vent bivalves. Significant increase in the number of circulating haemocytes was detected from day 5 after induction shell regeneration. It is suggested that the increase may be a result of migration of haemocytes from the connective tissue, probably to the shell growth frontline. It is alleged that a first peak in haemocyte number is a non-specific immune response related wound healing, which renders changes in the pallial fluid that are favourable for CaCO₃ deposition. The conspicuous presence of an unidentified, acid soluble, highly refractive structure in the haemolymph of induced mussels was detected, which may play a role in Ca nucleation.This study has set the stage for investigations underway on the influence of hydrostatic pressure on shell biomineralisation in B. azoricus subjected to post-capture hyperbaric simulations.     

Microbial diversity of a sulphide spire located in the Edmond deep-sea hydrothermal vent field on the Central Indian Ridge

A culture‐independent molecular phylogenetic survey was carried out for a bacterial and archaeal community of a mineralized crust coating a sulphide spire, which was collected from the Edmond vent field (23° S, 69° E, 3300 m depth) on the Central Indian Ridge. Small‐subunit rRNA genes (16S rDNA) were amplified from environmental DNA by PCR utilizing Bacteria‐specific, and Archaea‐specific 16S rDNA primers. PCR products were cloned and 26 bacterial and nine archaeal unique sequence types (phylotypes) were identified from 150 clones analysed by restriction fragment length polymorphism, representing eight and four distinct lineages, respectively. The majority (>90%) of the bacterial phylotypes group with the ?‐Proteobacteria and confirms the global prevalence of ?‐Proteobacteria in deep‐sea hydrothermal environments. Among the ?‐Proteobacteria, >40% of the phylotypes were closely related to the recently isolated deep‐sea vent thermophilic chemolithoautotrophic sulphur‐reducer, Nautilia lithotrophica. A single bacterial sequence was nearly identical (99% similarity) to the thermophilic hydrogen‐oxidizing Hydrogenobacter thermolithotrophum, and is the first report of Hydrogenobacter at deep‐sea hydrothermal vents. A majority (97%) of the archaeal phylotypes grouped with the ‘Deep‐sea Hydrothermal Vent Euryarchaeotal Group’, a phylogenetic lineage of uncultured Archaea that have only been reported from other deep‐sea hydrothermal vents on the Mid‐Atlantic Ridge, East Pacific Rise, Juan de Fuca Ridge, Isu–Ogasawara Arc, Okinawa Trough and the Manus Basin. A single sequence was closely related to the hyperthermophilic sulphur‐reducing Thermococcales frequently found in diverse deep‐sea vent environments. Scanning electron micrographs of the mineralized crust reveal abundant filamentous, rod and coccoidal forms encased in sulphur and sulphide mineral precipitate, suggesting that the thermophilic chemolithoautorophs and sulphide‐producing heterotrophs may influence the architecture and sulphur cycling of the sulphide spire.     

Description of a new family,new genus,and two new species of deep‐sea Forcipulatacea (Asteroidea), including the first known sea star from hydrothermal vent habitats

Based on a phylogenetic analysis of undescribed taxa within the Forcipulatacea, a new family of deep‐sea forcipulatacean starfishes, Paulasteriidae fam. nov., is described from deep‐sea settings. Paulasterias tyleri gen. et sp. nov. was observed at recently documented hydrothermal vents on the East Scotia Ridge, Southern Ocean. A second species, Paulasterias mcclaini gen. et sp. nov. was observed in deep‐sea settings in the North Pacific, more distant from hydrothermal vents. Both species are multi‐armed (with between six and eight arms), with a fleshy body wall, and a poorly developed or absent adoral carina. Here, we include discussions of pedicellariae morphology, feeding biology, and classification. © 2015 The Linnean Society of London     

Biomarkers Reveal Diverse Microbial Communities in Black Smoker Sulfides from Turtle Pits (Mid-Atlantic Ridge,Recent) and Yaman Kasy (Russia,Silurian)

The steep biogeochemical gradients near deep sea hydrothermal vents provide various niches for microbial life. Here we present biosignatures of such organisms enclosed in a modern and an ancient hydrothermal sulfide deposit (Turtle Pits, Mid-Atlantic Ridge, Recent; Yaman Kasy, Russia, Silurian). In the modern sulfide we found high amounts of specific bacterial and archaeal biomarkers with δ¹³C values between ?8 and ?37‰ VPDB. Our data indicate the presence of thermophilic members of the autotrophic Aquificales using the reductive tricarboxylic acid (rTCA) cycle as well as of methanogenic and chemolithoheterotrophic Archaea. In the ancient sample, most potential biomarkers of thermophiles were obscured by compounds derived from allochthonous organic matter (OM), except for an acyclic C₄₀ biphytane and its C₃₉ breakdown product. Both samples contained high amounts of unresolved complex mixtures (UCM) of hydrocarbons. Apparently, OM in the sulfides had to withstand high thermal stress, indicated by highly mature hopanes, steranes, and cheilanthanes with up to 41 carbon atoms.     

Diversity in mussel beds at deep-sea hydrothermal vents and cold seeps

Remarkably little is known about fundamental distinctions (or similarities) between the faunas of deep‐sea hydrothermal vents and seeps. Low species richness at vents has been attributed to the transient nature of vent habitats and to toxic effects of hydrogen sulphide and heavy metals in vent effluents. Seeps are arguably more stable and more chemically benign than vents. They have also been regarded as more diverse, but until now there has not been a rigorous test of this hypothesis. We evaluated diversity indices for invertebrates associated with mussel beds at six vents and two seeps and found that invertebrate diversity was significantly higher at seeps than vents, although some vent mussel beds supported nearly the same diversity as seep mussel beds. Lower diversity at vents may be a consequence of a greater physiological barrier to invasion at vents than at seeps. Diversity was lowest where spacing between vents was greatest, suggesting that risks of extinction as a result of dispersal‐related processes may contribute to the pattern of diversity observed at vents.     

基于宏基因组学重建来自深海热液喷口的Epsilonproteobacteria基因组及其代谢分析

【背景】非致病性Epsilonproteobacteria广泛存在于全球各种不同的自然环境中,特别是一些极端生境如深海热液喷口,并且经常在微生物群落中作为优势物种被发现。然而,由于现阶段培养技术的限制,仅有为数不多的深海热液Epsilonproteobacteria被分离培养,极大限制了对其生理特征、代谢方式以及生态功能的深入认识。【目的】研究深海热液未培养Epsilonproteobacteria的进化地位、代谢潜能及其在原位生态系统中可能发挥的作用。【方法】基于宏基因组学Binning的方法,从采集自东太平洋海隆深海热液烟囱体样本中构建4个高质量的Epsilonproteobacteria基因组Bin225、Bin51、Bin54和Bin189,并进行了系统发育和代谢途径的分析。【结果】Bin189在系统发育树上相对独立于其他所有已知的Epsilonproteobacteria类群,而其余3个重构基因组都与Nitratiruptor sp. SB155-2具有较近的亲缘关系。在代谢潜能方面,所有的基因组除了都含有sqr硫氧化和rTCA碳固定途径的基因以外,也同时具有脂多糖输出转运子和多种分泌系统。Bin189显示出与其它基因组显著不同的代谢特征,其中还检测到与有机物和氨基酸转运相关的功能基因。而其他的3个基因组均具有完整的反硝化途径的功能基因,其中2个还具有Sox系统、氢化酶和鞭毛移动系统。【结论】Bin189可能是一种新发现的深海热液兼性化能营养型Epsilonproteobacteria,推测其余的3个类群能够利用硫化物和氢气作为能源进行化能自养生长。考虑到它们多样的代谢潜能,这些Epsilonproteobacteria类群很可能在深海热液微生物群落的形成发展和地球化学元素循环中发挥重要作用。     

Off-axis symbiosis found: Characterization and biogeography of bacterial symbionts of Bathymodiolus mussels from Lost City hydrothermal vents

Organisms at hydrothermal vents inhabit discontinuous chemical 'islands' along mid-ocean ridges, a scenario that may promote genetic divergence among populations. The 2003 discovery of mussels at the Lost City Hydrothermal Field provided a means of evaluating factors that govern the biogeography of symbiotic bacteria in the deep sea. The unusual chemical composition of vent fluids, the remote location, and paucity of characteristic vent macrofauna at the site, raised the question of whether microbial symbioses existed at the extraordinary Lost City. If so, how did symbiotic bacteria therein relate to those hosted by invertebrates at the closest known hydrothermal vents along the Mid-Atlantic Ridge (MAR)? To answer these questions, we performed microscopic and molecular analyses on the bacteria found within the gill tissue of Bathymodiolus mussels (Mytilidae, Bathymodiolinae) that were discovered at the Lost City. Here we show that Lost City mussels harbour chemoautotrophic and methanotrophic endosymbionts simultaneously. Furthermore, populations of the chemoautotrophic symbionts from the Lost City and two sites along the MAR are genetically distinct from each other, which suggests spatial isolation of bacteria in the deep sea. These findings provide new insights into the processes that drive diversification of bacteria and evolution of symbioses at hydrothermal vents.     

Bacterial Populations (First Record) at Two Shallow Hydrothermal Vents of the Mexican Pacific West Coast

Thermophilic and metal-oxidizing bacteria were identified in shallow hydrothermal vents on the western Mexican coast. The role of these bacteria in biomineralization processes observed in the vents is explained, and the effect of the vents on biodiversity of prokaryotes is discussed. Research was done at two shallow hydrothermal vent sites: Bahía Concepción (BC) in the Baja California Peninsula and Punta Mita (PM), on the central Pacific coast. Temperature at the sediments proximal to the vents was similar, but the redox potentials (0.5 V in BC and ?0.3 V in PM) and pH (6.2 in BC and as low as 4.5 in PM) differed. The composition of the discharged water ranged from nearly seawater to lower-salinity fluids, and the gas phase was mainly CO₂ at BC and N₂ and CH₄ at PM. The study focuses on the biogeochemical processes related to the different species of bacteria present in the studied sites, which are involved in the anaerobic oxidation of methane (AOM), seawater sulfate reduction, and metal oxidation. The detected bacterial lineages represented typical deep vent species, which disproves a previous hypothesis that proposed that different consortia were populating deep and shallow hydrothermal vents. The results obtained here show that the main parameter affecting the bacterial groups present in shallow vents was the redox potential: gamma-, delta-, and epsilon proteobacteria as well as Bacteriodetes are present under the oxidizing conditions of BC, and Thermotogae, Aquificae, and Planctomycetes are present in PM. Sunlight abundance favored the prevalence of halophilic and Chlorofleaxae bacteria in both areas.     

Growth and phylogenetic properties of novel bacteria belonging to the epsilon subdivision of the Proteobacteria enriched from Alvinella pompejana and deep-sea hydrothermal vents

Recent molecular characterizations of microbial communities from deep-sea hydrothermal sites indicate the predominance of bacteria belonging to the epsilon subdivision of Proteobacteria (epsilon Proteobacteria). Here, we report the first enrichments and characterizations of four epsilon Proteobacteria that are directly associated with Alvinella pompejana, a deep sea hydrothermal vent polychete, or with hydrothermal vent chimney samples. These novel bacteria were moderately thermophilic sulfur-reducing heterotrophs growing on formate as the energy and carbon source. In addition, two of them (Am-H and Ex-18.2) could grow on sulfur lithoautrotrophically using hydrogen as the electron donor. Optimal growth temperatures of the bacteria ranged from 41 to 45 degrees C. Phylogenetic analysis of the small-subunit ribosomal gene of the two heterotrophic bacteria demonstrated 95% similarity to Sulfurospirillum arcachonense, an epsilon Proteobacteria isolated from an oxidized marine surface sediment. The autotrophic bacteria grouped within a deeply branching clade of the epsilon Proteobacteria, to date composed only of uncultured bacteria detected in a sample from a hydrothermal vent along the mid-Atlantic ridge. A molecular survey of various hydrothermal vent environments demonstrated the presence of two of these bacteria (Am-N and Am-H) in more than one geographic location and habitat. These results suggest that certain epsilon Proteobacteria likely fill important niches in the environmental habitats of deep-sea hydrothermal vents, where they contribute to overall carbon and sulfur cycling at moderate thermophilic temperatures.     

Comparison of thermophilic methanogens from submarine hydrothermal vents

An extremely thermophilic methanogen was isolated from hydrothermal vent sediment (80°–120° C) collected from the Guaymas Basin, Gulf of California, at a depth of approximately 2000 m. The isolate was a characteristic member of the genus Methanococcus based on its coccoid morphology, ability to produce methane from CO₂ and H₂, and DNA base composition (31.4 mol% G+C); it is distinguished from previously described extremely thermophilic vent methanogens by its ability to grow and produce methane from formate and in the composition of membrane lipids. The temperature range for growth was 48°–94° C (optimum near 85° C); the pH optimum was 6.0. The isolate grew autotrophically but was stimulated by selenium and growth nutrients supplied by yeast extract and trypticase. Extracted polar lipids consisted primarily of diphytanyl glycerol diether (62%), macrocyclic glycerol diether (15.3%), and dibiphytanyl glycerol tetraether (11.8%). Neutral lipids were dominated by a series of C₃₀ isoprenoids; in addition, a novel series of C₃₅ isoprenoids were detected. The isolate appears to be a close relative of the previously described Methanococcus jannaschii, isolated from the East Pacific Rise hydrothermal vent system. From the frequency of isolation, it appears that extremely thermophilic methanococci are the predominant representatives of the methanogenic archaebacteria occurring at deep sea hydrothermal vents.     

Strain-level genomic variation in natural populations of Lebetimonas from an erupting deep-sea volcano

Chemolithoautotrophic Epsilonproteobacteria are ubiquitous in sulfidic, oxygen-poor habitats, including hydrothermal vents, marine oxygen minimum zones, marine sediments and sulfidic caves and have a significant role in cycling carbon, hydrogen, nitrogen and sulfur in these environments. The isolation of diverse strains of Epsilonproteobacteria and the sequencing of their genomes have revealed that this group has the metabolic potential to occupy a wide range of niches, particularly at dynamic deep-sea hydrothermal vents. We expand on this body of work by examining the population genomics of six strains of Lebetimonas, a vent-endemic, thermophilic, hydrogen-oxidizing Epsilonproteobacterium, from a single seamount in the Mariana Arc. Using Lebetimonas as a model for anaerobic, moderately thermophilic organisms in the warm, anoxic subseafloor environment, we show that genomic content is highly conserved and that recombination is limited between closely related strains. The Lebetimonas genomes are shaped by mobile genetic elements and gene loss as well as the acquisition of novel functional genes by horizontal gene transfer, which provide the potential for adaptation and microbial speciation in the deep sea. In addition, these Lebetimonas genomes contain two operons of nitrogenase genes with different evolutionary origins. Lebetimonas expressed nifH during growth with nitrogen gas as the sole nitrogen source, thus providing the first evidence of nitrogen fixation in any Epsilonproteobacteria from deep-sea hydrothermal vents. In this study, we provide a comparative overview of the genomic potential within the Nautiliaceae as well as among more distantly related hydrothermal vent Epsilonproteobacteria to broaden our understanding of microbial adaptation and diversity in the deep sea.     

Growth and Phylogenetic Properties of Novel Bacteria Belonging to the Epsilon Subdivision of the Proteobacteria Enriched from Alvinella pompejana and Deep-Sea Hydrothermal Vents

Recent molecular characterizations of microbial communities from deep-sea hydrothermal sites indicate the predominance of bacteria belonging to the epsilon subdivision of Proteobacteria (epsilon Proteobacteria). Here, we report the first enrichments and characterizations of four epsilon Proteobacteria that are directly associated with Alvinella pompejana, a deep sea hydrothermal vent polychete, or with hydrothermal vent chimney samples. These novel bacteria were moderately thermophilic sulfur-reducing heterotrophs growing on formate as the energy and carbon source. In addition, two of them (Am-H and Ex-18.2) could grow on sulfur lithoautrotrophically using hydrogen as the electron donor. Optimal growth temperatures of the bacteria ranged from 41 to 45°C. Phylogenetic analysis of the small-subunit ribosomal gene of the two heterotrophic bacteria demonstrated 95% similarity to Sulfurospirillum arcachonense, an epsilon Proteobacteria isolated from an oxidized marine surface sediment. The autotrophic bacteria grouped within a deeply branching clade of the epsilon Proteobacteria, to date composed only of uncultured bacteria detected in a sample from a hydrothermal vent along the mid-Atlantic ridge. A molecular survey of various hydrothermal vent environments demonstrated the presence of two of these bacteria (Am-N and Am-H) in more than one geographic location and habitat. These results suggest that certain epsilon Proteobacteria likely fill important niches in the environmental habitats of deep-sea hydrothermal vents, where they contribute to overall carbon and sulfur cycling at moderate thermophilic temperatures.     

High potential for temperate viruses to drive carbon cycling in chemoautotrophy‐dominated shallow‐water hydrothermal vents

Viruses are the most abundant life forms in the world's oceans and they are key drivers of biogeochemical cycles, but their impact on the microbial assemblages inhabiting hydrothermal vent ecosystems is still largely unknown. Here, we analysed the viral life strategies and virus‐host interactions in the sediments of a newly discovered shallow‐water hydrothermal field of the Mediterranean Sea. Our study reveals that temperate viruses, once experimentally induced to replicate, can cause large mortality of vent microbes, significantly reducing the chemoautotrophic carbon production, while enhancing the metabolism of microbial heterotrophs and the re‐cycling of the organic matter. These results provide new insights on the factors controlling primary and secondary production processes in hydrothermal vents, suggesting that the inducible provirus‐host interactions occurring in these systems can profoundly influence the functioning of the microbial food web and the efficiency in the energy transfer to the higher trophic levels.     

Methane- and sulfur-metabolizing microbial communities dominate the Lost City hydrothermal field ecosystem

Hydrothermal venting and the formation of carbonate chimneys in the Lost City hydrothermal field (LCHF) are driven predominantly by serpentinization reactions and cooling of mantle rocks, resulting in a highly reducing, high-pH environment with abundant dissolved hydrogen and methane. Phylogenetic and terminal restriction fragment length polymorphism analyses of 16S rRNA genes in fluids and carbonate material from this site indicate the presence of organisms similar to sulfur-oxidizing, sulfate-reducing, and methane-oxidizing Bacteria as well as methanogenic and anaerobic methane-oxidizing Archaea. The presence of these metabolic groups indicates that microbial cycling of sulfur and methane may be the dominant biogeochemical processes active within this ultramafic rock-hosted environment. 16S rRNA gene sequences grouping within the Methylobacter and Thiomicrospira clades were recovered from a chemically diverse suite of carbonate chimney and fluid samples. In contrast, 16S rRNA genes corresponding to the Lost City Methanosarcinales phylotype were found exclusively in high-temperature chimneys, while a phylotype of anaerobic methanotrophic Archaea (ANME-1) was restricted to lower-temperature, less vigorously venting sites. A hyperthermophilic habitat beneath the LCHF may be reflected by 16S rRNA gene sequences belonging to Thermococcales and uncultured Crenarchaeota identified in vent fluids. The finding of a diverse microbial ecosystem supported by the interaction of high-temperature, high-pH fluids resulting from serpentinization reactions in the subsurface provides insight into the biogeochemistry of what may be a pervasive process in ultramafic subseafloor environments.