The role of hydrodynamics for the spatial distribution of high-temperature hydrothermal vent-endemic fauna in the deep ocean environment.

Active hydrothermal vents provide the surrounding submarine environment with substantial amounts of matter and energy, thus serving as important habitats for diverse megabenthic communities in the deep ocean and constituting a unique, highly productive chemosynthetic ecosystem on Earth. Vent-endemic biological communities gather near the venting site and are usually not found beyond a distance of the order of 100 m from the vent. This is surprising because one would actually expect matter ejected from high-temperature vents, which generate highly turbulent buoyancy plumes, to be suspended and carried far away by the plume flows and deep-sea currents. Here, we study this problem from a fluid dynamics perspective by simulating the vent hydrodynamics using a numerical model that couples the plume flow with induced matter and energy transport. We find that both low- and high-temperature vents deposit most vent matter relatively close to the plume. In particular, the tendency of turbulent buoyancy plumes to carry matter far away is strongly counteracted by generated entrainment flows back into the plume stem. The deposition ranges of organic and inorganic hydrothermal particles obtained from the simulations for various natural high-temperature vents are consistent with the observed maximum spatial extent of biological communities, evidencing that plume hydrodynamics exercises strong control over the spatial distribution of vent-endemic fauna. While other factors affecting the spatial distribution of vent-endemic fauna, such as geology and geochemistry, are site-specific, the main physical features of plume hydrodynamics unraveled in this study are largely site-unspecific and therefore universal across vent sites on Earth.

Revealing the response of microbial communities to polyethylene micro(nano)plastics exposure in cold seep sediment.

To date, multiple studies have shown that the accumulation of microplastics (MPs)/nanoplastics (NPs) in the environment may lead to various problems. However, the effects of MPs/NPs on microbial communities and biogeochemical processes, particularly methane metabolism in cold seep sediments, have not been well elucidated. In this study, an indoor microcosm experiment for a period of 120 days exposure of MPs/NPs was conducted. The results showed that MPs/NPs addition did not significantly influence bacterial and archaeal richness in comparison with the control (p > 0.05), whereas higher levels of NPs (1 %, w/w) had a significant adverse effect on bacterial diversity (p < 0.05). Moreover, the bacterial community was more sensitive to the addition of MPs/NPs than the archaea, and Epsilonbacteraeota replaced Proteobacteria as the dominant phylum in the MPs/NPs treatments (except 0.2 % NPs). With respect to the co-occurrence relationships, network analysis showed that the presence of NPs, in comparison with MPs, reduced microbial network complexity. Finally, the presence of MPs/NPs decreased the abundance of mcrA, while promoting the abundance of pmoA. This study will help elucidate the responses of microbial communities to MPs/NPs and evaluate their effects on methane metabolism in cold seep ecosystems.

Potential autotrophic carbon-fixer and Fe(II)-oxidizer Alcanivorax sp. MM125-6 isolated from Wocan hydrothermal field.

The genus Alcanivorax is common in various marine environments, including in hydrothermal fields. They were previously recognized as obligate hydrocarbonoclastic bacteria, but their potential for autotrophic carbon fixation and Fe(II)-oxidation remains largely elusive. In this study, an in situ enrichment experiment was performed using a hydrothermal massive sulfide slab deployed 300 m away from the Wocan hydrothermal vent. Furthermore, the biofilms on the surface of the slab were used as an inoculum, with hydrothermal massive sulfide powder from the same vent as an energy source, to enrich the potential iron oxidizer in the laboratory. Three dominant bacterial families, Alcanivoraceae, Pseudomonadaceae, and Rhizobiaceae, were enriched in the medium with hydrothermal massive sulfides. Subsequently, strain Alcanivorax sp. MM125-6 was isolated from the enrichment culture. It belongs to the genus Alcanivorax and is closely related to Alcanivorax profundimaris ST75FaO-1 T (98.9% sequence similarity) indicated by a phylogenetic analysis based on 16S rRNA gene sequences. Autotrophic growth experiments on strain MM125-6 revealed that the cell concentrations were increased from an initial 7.5 × 105 cells/ml to 3.13 × 108 cells/ml after 10 days, and that the δ13C VPDB in the cell biomass was also increased from 234.25‰ on day 2 to gradually 345.66 ‰ on day 10. The gradient tube incubation showed that bands of iron oxides and cells formed approximately 1 and 1.5 cm, respectively, below the air-agarose medium interface. In addition, the SEM-EDS data demonstrated that it can also secrete acidic exopolysaccharides and adhere to the surface of sulfide minerals to oxidize Fe(II) with NaHCO3 as the sole carbon source, which accelerates hydrothermal massive sulfide dissolution. These results support the conclusion that strain MM125-6 is capable of autotrophic carbon fixation and Fe(II) oxidization chemoautotrophically. This study expands our understanding of the metabolic versatility of the Alcanivorax genus as well as their important role(s) in coupling hydrothermal massive sulfide weathering and iron and carbon cycles in hydrothermal fields.

Endosymbiont population genomics sheds light on transmission mode, partner specificity, and stability of the scaly-foot snail holobiont.

The scaly-foot snail (Chrysomallon squamiferum) inhabiting deep-sea hydrothermal vents in the Indian Ocean relies on its sulphur-oxidising gammaproteobacterial endosymbionts for nutrition and energy. In this study, we investigate the specificity, transmission mode, and stability of multiple scaly-foot snail populations dwelling in five vent fields with considerably disparate geological, physical and chemical environmental conditions. Results of population genomics analyses reveal an incongruent phylogeny between the endosymbiont and mitochondrial genomes of the scaly-foot snails in the five vent fields sampled, indicating that the hosts obtain endosymbionts via horizontal transmission in each generation. However, the genetic homogeneity of many symbiont populations implies that vertical transmission cannot be ruled out either. Fluorescence in situ hybridisation of ovarian tissue yields symbiont signals around the oocytes, suggesting that vertical transmission co-occurs with horizontal transmission. Results of in situ environmental measurements and gene expression analyses from in situ fixed samples show that the snail host buffers the differences in environmental conditions to provide the endosymbionts with a stable intracellular micro-environment, where the symbionts serve key metabolic functions and benefit from the host's cushion. The mixed transmission mode, symbiont specificity at the species level, and stable intracellular environment provided by the host support the evolutionary, ecological, and physiological success of scaly-foot snail holobionts in different vents with unique environmental parameters.

Thermosipho ferrireducens sp.nov., an anaerobic thermophilic iron(III)-reducing bacterium isolated from a deep-sea hydrothermal sulfide deposits.

A thermophilic, anaerobic, iron-reducing bacterium strain JL129W03T (=KCTC 15905T=MCCC 1A14213T) was isolated from a sulfide sample collected from the Daxi hydrothermal field (60.5° E, 6.4° N, 2919 m depth) on the Carlsberg Ridge, northwest Indian Ocean. Cells grew at 55-75 °C(optimum, 70 °C), at pH 6.0-9.0 (optimum, pH 6.0-7.0) and at NaCl concentrations of 1.5-4.5 % (w/v; optimum 3.0 %). Under optimal growth conditions, the generation time was around 85 min. The isolate was an obligate chemoorganoheterotroph, utilizing complex organic compounds, carbohydrates, organic acids and one amino acid. It was anaerobic and facultatively dependent on elemental sulphur and various forms of Fe(III) as an electron acceptor: insoluble forms and soluble forms. It did not reduce sulfite, sulphate, thiosulfate or nitrate. The G+C content of its genomic DNA was 34.0 mol%. Phylogenetic 16S rRNA gene sequence analyses revealed that its closest relative was Thermosipho atlanticus DV1140T with 95.81 % 16S rRNA sequence similarity. On the basis of physiological distinctness and phylogenetic distance, the isolate is considered to represent a novel species of the genus Thermosipho, for which the name Thermosipho ferrireducens sp. nov. is proposed. The type strain is strain JL129W03T (=KCTC 15905T;=MCCC 1A14213T).

Sulfurovum indicum sp. nov., a novel hydrogen- and sulfur-oxidizing chemolithoautotroph isolated from a deep-sea hydrothermal plume in the Northwestern Indian Ocean.

A novel mesophilic, hydrogen-, and sulfur-oxidizing bacterium, designated strain ST-419T, was isolated from a deep-sea hydrothermal vent plume on the Carlsberg Ridge of the Northwestern Indian Ocean. The isolate was a Gram-staining-negative, non-motile and coccoid to oval-shaped bacterium. Growth was observed at 4-50 °C (optimum 37 °C), pH 5.0-8.6 (optimum pH 6.0) and 1.0-5.0 % (w/v) NaCl (optimum 3.0 %). ST-419T could grow chemlithoautotrophically with molecular hydrogen, sulfide, elemental sulfur and thiosulfate as energy sources. Molecular oxygen, nitrate and elemental sulfur could be used as electron acceptors. The predominant fatty acids were C16 : 1ω7c, C18 : 1ω7c and C16 : 0. The major polar lipids were phosphatidylethanolamine, diphosphatidylglycerol and phosphatidylglycerol. The respiratory quinone was menaquinone MK-6 and the G+C content of the genomic DNA was 42.4 mol%. Phylogenetic analysis based on 16S rRNA gene sequences revealed that ST-419T represented a member of genus Sulfurovum and was most closely related to Sulfurovum riftiae 1812ET, with 97.6 % sequence similarity. The average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values between ST-419T and S. riftiae 1812ET were 74.6 and 19.6 %, respectively. The combined genotypic and phenotypic data indicate that ST-419T represents a novel species within the genus Sulfurovum, for which the name Sulfurovum indicum sp. nov. is proposed. The type strain is ST-419T (=MCCC 1A17954T=KCTC 25164T).

Variability of the Indonesian Throughflow in the Makassar Strait over the Last 30 ka.

The hydrological characteristics, including temperatures and salinities, of the upper water over the last 30 ka from two sites connected by the Indonesian Throughflow (ITF) across the Makassar Strait are reconstructed and compared. The thermocline hydrological gradient in the strait was larger during 13.4~19 ka BP and 24.2~27 ka BP than that in the Holocene. The weakened ITF during those periods in the last glacial period, corresponding to the decreased trade wind stress under an El Niño-like climate mean state, likely accounts for the increased thermocline gradient. The thermocline water temperature variabilities of the two sites, in particular the highest peaks at ~7 ka BP, are different from the records of the open western Pacific. Reoccurrence of the South China Sea Throughflow and thus a decreased surface throughflow along the Makassar Strait perhaps led to a warmer peak of thermocline temperature at ~7 ka BP than at ~11 ka BP.

Brevibacterium sediminis sp. nov., isolated from deep-sea sediments from the Carlsberg and Southwest Indian Ridges.

Three actinobacterial strains, FXJ8.128, FXJ8.269T and FXJ8.309, were isolated from deep-sea sediments collected from the Carlsberg Ridge and Southwest Indian Ridge at depths of 3690, 1800 and 2461 m, respectively. The three strains had highly similar 16S rRNA gene sequences (99.8-99.9 % identities) and formed a monophyletic clade within the Brevibacterium 16S rRNA gene tree, showing 98.2-98.9 % 16S rRNA gene sequence identities with type strains Brevibacterium epidermidis NCIMB 702286T, Brevibacterium iodinum DSM 20626T, Brevibacterium linens DSM 20425T, Brevibacterium oceani BBH7T and Brevibacterium permense VKM Ac-2280T. All three isolates showed activity towards the breakdown of pectin and fluoranthene. They contained MK-8(H2) as the most predominant menaquinone, diphosphatidylglycerol, phosphatidylglycerol and a glycolipd as the main polar lipids, and anteiso-C15 : 0 and anteiso-C17 : 0 as the major cellular fatty acids. Moreover, the three isolates were distinguished readily from the phylogenetically related type strains by DNA-DNA hybridization values, by random amplified polymorphic DNA fingerprint profiles and by a range of physiological and biochemical characteristics. On the basis of the above polyphasic taxonomic data, strains FXJ8.128, FXJ8.269T and FXJ8.309 represent a novel species of the genus Brevibacterium, for which the name Brevibacterium sediminis sp. nov. is proposed. The type strain is FXJ8.269T (=CGMCC 1.15472T=DSM 102229T).

Bacillus oceani sp. nov., isolated from seawater.

Two Gram-staining-positive, endospore-forming, rod-shaped bacterial strains, designated strain SW109T and strain W006, were isolated from a seawater sample collected from the Indian Ocean. The strains were strictly aerobic, catalase- and oxidase-positive and motile by peritrichous flagella. The predominant cellular fatty acids (>10 %) were anteiso-C15 : 0, iso-C15 : 0 and iso-C14 : 0. The major menaquinone was menaquinone-7 (MK-7) and the major polar lipids were diphosphatidylglycerol, phosphatidylglycerol and phosphatidylethanolamine. The genomic DNA G+C content of strain SW109T and strain W006 was 46.3 and 46.1 mol%, respectively. Phylogenetic analyses based on 16S rRNA gene sequences indicated that the two strains represented a novel member of the genus Bacillus, showing the highest similarity with Bacillus halodurans LMG 7121T and Bacillus okuhidensis DSM 13666T (96.4 and 96.2 % sequence similarity, respectively). On the basis of phylogenetic inference and phenotypic characteristics, it is proposed that the two strains represent a novel species of the genus Bacillus, for which the name Bacillus oceani sp. nov. is proposed. The type strain is SW109T ( = CGMCC 1.12347T = DSM 100579T).

Belliella marina sp. nov., isolated from seawater.

Gram-stain-negative, rod-shaped bacterium, strain SW112T, was isolated from a seawater sample collected from the Indian Ocean. The strain was strictly aerobic and catalase- and oxidase-positive. Strain SW112T grew at 4-42 °C (optimum 30 °C), at pH 5.5-9.5 (optimum pH 7.5) and in the presence of 0-9.0 % (w/v) NaCl (optimum 2.0-3.0 %). The predominant cellular fatty acids were iso-C15 : 0 (29.7 %), iso-C17 : 03-OH (14.3 %) and summed feature 3 (comprising C16 : 1ω7c and/or C16 : 1ω6c, 15.1 %). The major menaquinone was menaquinone-7 and the major polar lipid was phosphatidylethanolamine. The genomic DNA G+C content of strain SW112T was 39 mol%. Phylogenetic analyses based on 16S rRNA gene sequences revealed that strain SW112T was related to members of the genus Belliella, showing the highest similarity with Belliella aquatica TS-T86T and Belliella baltica DSM 15883T (96.5 % and 96.4 %sequence similarity, respectively). On the basis of phylogenetic inference and phenotypic characteristics, it is proposed that strain SW112T represents a novel species of the genus Belliella, for which the name Belliella marina sp. nov. is proposed. The type strain is SW112T(=CGMCC 1.15180T=KCTC 33694T).