Discovery of deep-sea acoels from a chemosynthesis-based ecosystem.

Chemosynthesis-based ecosystems such as hydrothermal vents and hydrocarbon seeps harbour various endemic species, each uniquely adapted to the extreme conditions. While some species rely on obligatory relationships with bacterial symbionts for nutrient uptake, scavengers and predators also play important roles in food web dynamics in these ecosystems. Acoels, members of the phylum Xenacoelomorpha, are simple, worm-like invertebrates found in marine environments worldwide but are scarcely understood taxa. This study presents a novel genus and species of acoel from a deep-sea hydrocarbon seep off Hatsushima, Japan, Hoftherma hatsushimaensis gen. et sp. nov. Our multi-locus phylogenetic analysis revealed that the acoels are nested within Hofsteniidae, a family previously known exclusively from shallow waters. This finding suggests that at least two independent colonization events occurred in the chemosynthesis-based environments from the phylum Xenoacoelomorpha, represented by hofsteniid acoels and Xenoturbella. Previous reports of hofsteniid species from low-oxygen and sulfide-rich environments, including intertidal habitats with decomposing leaves, in addition to H. hatsushimaensis gen. et sp. nov. from a deep-sea hydrocarbon seep, imply a common ancestral adaptation to sulfide-rich ecosystems within Hofsteniidae. Moreover, the sister relationship between solenofilomorphid acoels predominating in sulfide-rich habitats indicates common ancestral adaptation to sulfide-rich ecosystems between these two families.

Methylomarinovum caldicuralii gen. nov., sp. nov., a moderately thermophilic methanotroph isolated from a shallow submarine hydrothermal system, and proposal of the family Methylothermaceae fam. nov.

A novel methane-oxidizing bacterium, strain IT-9(T), was isolated from a shallow submarine hydrothermal system occurring in a coral reef in Japan. Strain IT-9(T) was a Gram-negative, aerobic, motile, coccoid or oval-shaped bacterium with the distinctive intracytoplasmic membrane arrangement of a type I methanotroph. Strain IT-9(T) was a moderately thermophilic, obligate methanotroph that grew on methane and methanol at 30-55 °C (optimum 45-50 °C). The strain possessed the particulate methane monooxygenase (pMMO). The ribulose monophosphate pathway was operative for carbon assimilation. NaCl was required for growth within a concentration range of 1-5 % (optimum 3 %). The hao gene encoding hydroxylamine oxidoreductase (HAO) involved in nitrification was detected by a PCR experiment. The major phospholipid fatty acids were C16 : 0 and C18 : 1ω7c. The major isoprenoid quinone was Q-8. The DNA G+C content was 66.0 mol%. The 16S rRNA gene sequence of strain IT-9(T) was only moderately related to the sequences of members of the closest genera Methylohalobius (94.1 % similarity) and Methylothermus (91.7-91.9 % similarity); however, those sequences formed a deeply branching monophyletic group within the order Methylococcales. Phylogenies based on 16S rRNA gene sequences, deduced partial PmoA sequences and deduced partial Hao sequences and physiological and chemotaxonomic characteristics revealed that strain IT-9(T) represents a novel species of a new genus, for which the name Methylomarinovum caldicuralii gen. nov., sp. nov. is proposed. The type strain of Methylomarinovum caldicuralii is IT-9(T) ( = JCM 13666(T) = DSM 19749(T)). In addition, we propose a new family, Methylothermaceae fam. nov., in the order Methylococcales, to accommodate the genera Methylothermus, Methylohalobius and Methylomarinovum. The genera Methylothermus and Methylohalobius have been recognized as being distinct from other genera in the methane-oxidizing order Methylococcales in the class Gammaproteobacteria. These genera form a distinctive monophyletic lineage within the order on the basis of 16S rRNA gene sequence phylogeny. This seems consistent with their distinctive physiological traits; the genus Methylothermus includes the most thermophilic species, and the genus Methylohalobius includes the most halophilic species, within the order. Although these two genera include only three species at the time of writing, similar sequences of 16S rRNA genes and pmoA genes encoding pMMO have been detected in a geothermal area or deep-sea hydrothermal vent fields by studies using culture-independent techniques. This suggests that unknown methanotrophs of this lineage inhabit various extreme environments.

Methylomarinum vadi gen. nov., sp. nov., a methanotroph isolated from two distinct marine environments.

Two aerobic methane-oxidizing bacterial strains were isolated from distinct marine environments in Japan. Strains IT-4(T) and T2-1 were Gram-stain-negative, aerobic, motile, plump short rods or oval-shaped bacteria with a single polar flagellum and type I intracytoplasmic membranes. They were obligate methanotrophs that grew only on methane or methanol. Each strain possessed the particulate methane monooxygenase (pMMO). The ribulose monophosphate pathway was operative for carbon assimilation. The strains grew best at 37 °C, and did not grow at 45 °C. NaCl was required for growth within a concentration range of 1-8 % (w/v). The major phospholipid fatty acids were C16 : 0, C16 : 1ω7c, and C16 : 1ω5t. The major isoprenoid quinone was MQ-8. The DNA G+C content was 50.9-51.7 mol%. The 16S rRNA gene sequences of the strains showed 99.4 % similarity to each other, and DNA-DNA hybridization analysis indicated that the strains were representatives of the same species. The 16S rRNA gene sequences were highly similar to some marine environmental sequences (94.0-97.7 % similarity), but did not show similarities more than 94 % with sequences of members of other related genera, such as Methylomicrobium, Methylobacter, Methylomonas and Methylosarcina. Phylogenies based on 16S rRNA gene sequences and deduced partial PmoA sequences, and the physiological and chemotaxonomic characteristics revealed that strains IT-4(T) and T2-1 represent a novel species of a new genus in the family Methylococcaceae, for which the name Methylomarinum vadi gen. nov., sp. nov. is proposed. The type strain is IT-4(T) ( = JCM 13665(T) = DSM 18976(T)).

Spatial distribution of viruses associated with planktonic and attached microbial communities in hydrothermal environments.

Viruses play important roles in marine surface ecosystems, but little is known about viral ecology and virus-mediated processes in deep-sea hydrothermal microbial communities. In this study, we examined virus-like particle (VLP) abundances in planktonic and attached microbial communities, which occur in physical and chemical gradients in both deep and shallow submarine hydrothermal environments (mixing waters between hydrothermal fluids and ambient seawater and dense microbial communities attached to chimney surface areas or macrofaunal bodies and colonies). We found that viruses were widely distributed in a variety of hydrothermal microbial habitats, with the exception of the interior parts of hydrothermal chimney structures. The VLP abundance and VLP-to-prokaryote ratio (VPR) in the planktonic habitats increased as the ratio of hydrothermal fluid to mixing water increased. On the other hand, the VLP abundance in attached microbial communities was significantly and positively correlated with the whole prokaryotic abundance; however, the VPRs were always much lower than those for the surrounding hydrothermal waters. This is the first report to show VLP abundance in the attached microbial communities of submarine hydrothermal environments, which presented VPR values significantly lower than those in planktonic microbial communities reported before. These results suggested that viral lifestyles (e.g., lysogenic prevalence) and virus interactions with prokaryotes are significantly different among the planktonic and attached microbial communities that are developing in the submarine hydrothermal environments.

Kosmotoga arenicorallina sp. nov. a thermophilic and obligately anaerobic heterotroph isolated from a shallow hydrothermal system occurring within a coral reef, southern part of the Yaeyama Archipelago, Japan, reclassification of Thermococcoides shengliensis as Kosmotoga shengliensis comb. nov., and emended description of the genus Kosmotoga.

A novel thermophilic and sulfur-reducing bacterium, strain S304(T), was isolated from the Taketomi submarine hot spring shallow hydrothermal field located at southern part of the Yaeyama Archipelago, Japan. The cells were non-motile short thick rods or oval cocci 1.1-2.7 µm in length and 1.1-1.9 µm in width. Strain S304(T) was an obligately anaerobic heterotroph and sulfur reduction stimulates growth. Growth was observed between 50-65°C (optimum 60°C), pH 6.2-8.0 (optimum pH 7.1), 1.0-6.0% NaCl concentration (optimum 3.0%). The fatty acid composition was C(16:0) (71.4%), C(18:0) (20.9%) and C(18:1) (7.7%). The G + C content of genomic DNA was 40.8 mol%. The 16S rRNA gene sequence analysis indicated that strain S304(T) belonged to the genus Kosmotoga. Based on physiological and phylogenetic features of a new isolate, we propose new species in the genus Kosmotoga: the type strain of Kosmotoga arenicorallina sp. nov is S304(T) (=JCM 15790(T) = DSM22549(T)). Thermococcoides shengliensis 2SM-2(T) is phylogenetically associated with Kosmotoga olearia 14.5.1(T). Based on the phylogenetic relationship between Thermococcoides shengliensis 2SM-2(T) and Kosmotoga olearia 14.5.1(T), we propose the reclassification of Thermococcoides shengliensis as Kosmotoga shengliensis comb. nov. (type strain 2SM-2(T)). In addition, an emended description of the genus Kosmotoga is proposed.

Culture-dependent and -independent characterization of microbial communities associated with a shallow submarine hydrothermal system occurring within a coral reef off Taketomi Island, Japan.

Microbial communities in a shallow submarine hydrothermal system near Taketomi Island, Japan, were investigated using cultivation-based and molecular techniques. The main hydrothermal activity occurred in a craterlike basin (depth, approximately 23 m) on the coral reef seafloor. The vent fluid (maximum temperature, >52 degrees C) contained 175 microM H2S and gas bubbles mainly composed of CH4 (69%) and N2 (29%). A liquid serial dilution cultivation technique targeting a variety of metabolism types quantified each population in the vent fluid and in a white microbial mat located near the vent. The most abundant microorganisms cultivated from both the fluid and the mat were autotrophic sulfur oxidizers, including mesophilic Thiomicrospira spp. and thermophilic Sulfurivirga caldicuralii. Methane oxidizers were the second most abundant organisms in the fluid; one novel type I methanotroph exhibited optimum growth at 37 degrees C, and another novel type I methanotroph exhibited optimum growth at 45 degrees C. The number of hydrogen oxidizers cultivated only from the mat was less than the number of sulfur and methane oxidizers, although a novel mesophilic hydrogen-oxidizing member of the Epsilonproteobacteria was isolated. Various mesophilic to hyperthermophilic heterotrophs, including sulfate-reducing Desulfovibrio spp., iron-reducing Deferribacter sp., and sulfur-reducing Thermococcus spp., were also cultivated. Culture-independent 16S rRNA gene clone analysis of the vent fluid and mat revealed highly diverse archaeal communities. In the bacterial community, S. caldicuralii was identified as the predominant phylotype in the fluid (clonal frequency, 25%). Both bacterial clone libraries indicated that there were bacterial communities involved in sulfur, hydrogen, and methane oxidation and sulfate reduction. Our results indicate that there are unique microbial communities that are sustained by active chemosynthetic primary production rather than by photosynthetic production in a shallow hydrothermal system where sunlight is abundant.

Isolation and characterization of a thermophilic, obligately anaerobic and heterotrophic marine Chloroflexi bacterium from a Chloroflexi-dominated microbial community associated with a Japanese shallow hydrothermal system, and proposal for Thermomarinilinea lacunofontalis gen. nov., sp. nov.

A novel marine thermophilic and heterotrophic Anaerolineae bacterium in the phylum Chloroflexi, strain SW7(T), was isolated from an in situ colonization system deployed in the main hydrothermal vent of the Taketomi submarine hot spring field located on the southern part of Yaeyama Archipelago, Japan. The microbial community associated with the hydrothermal vent was predominated by thermophilic heterotrophs such as Thermococcaceae and Anaerolineae, and the next dominant population was thermophilic sulfur oxidizers. Both aerobic and anaerobic hydrogenotrophs including methanogens were detected as minor populations. During the culture-dependent viable count analysis in this study, an Anaerolineae strain SW7(T) was isolated from an enrichment culture at a high dilution rate. Strain SW7(T) was an obligately anaerobic heterotroph that grew with fermentation and had non-motile thin rods 3.5-16.5 µm in length and 0.2 µm in width constituting multicellular filaments. Growth was observed between 37-65°C (optimum 60°C), pH 5.5-7.3 (optimum pH 6.0), and 0.5-3.5% (w/v) NaCl concentration (optimum 1.0%). Based on the physiological and phylogenetic features of a new isolate, we propose a new species representing a novel genus Thermomarinilinea: the type strain of Thermomarinilinea lacunofontalis sp. nov., is SW7(T) (=JCM15506(T)=KCTC5908(T)).

Sulfurivirga caldicuralii gen. nov., sp. nov., a novel microaerobic, thermophilic, thiosulfate-oxidizing chemolithoautotroph, isolated from a shallow marine hydrothermal system occurring in a coral reef, Japan.

Novel thermophilic bacteria, designated strains VW1 and MM1(T), were isolated from hydrothermal fluid and microbial mat samples, respectively, collected from a shallow marine hydrothermal system (water depth 22 m) occurring in coral reefs off Taketomi Island, Okinawa, Japan. Cells of the two novel strains were motile rods with a single polar flagellum in the exponential growth phase. In a medium that included elemental sulfur, cells of the two strains became non-motile with oval to spherical cell shapes. For both strains, growth occurred at between 30 and 60 degrees C (optimum temperature of 50-55 degrees C; 60-80 min doubling time) and between pH 5.5 and 7.1 (optimum pH 6.0). The isolates were microaerobic chemolithoautotrophs capable of using thiosulfate or tetrathionate as the sole energy source, O(2) as the sole electron acceptor and CO(2) as the sole carbon source. Organic substrates, such as yeast extract and tryptone, inhibited growth of both strains. The G+C contents of genomic DNA were 51.3 and 49.5 mol% for strains VW1 and MM1(T), respectively. Phylogenetic analysis based on 16S rRNA gene sequences indicated that the two strains were closely related to each other (99.9 % sequence similarity) and were distantly related to other previously described genera within the Gammaproteobacteria. The novel isolates could also be differentiated from other gammaproteobacterial genera on the basis of their physiological properties. It is suggested that the novel isolates represent the type species of a new genus, for which the name Sulfurivirga caldicuralii gen. nov., sp. nov. (type strain MM1(T)=JCM 13439(T)=DSM 17737(T)) is proposed.