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).

Seasonal M2 Internal Tides in the Arabian Sea

Internal tides play a crucial role in ocean mixing. To explore the seasonal features of mode-1 M2 internal tides in the Arabian Sea, we analyzed their propagation and energy distribution using along-track sea-level anomaly data collected by satellite altimeters. We identified four primary source regions of internal tides: Abd al Kuri Island, the Carlsberg Ridge, the northeastern Arabian Sea, and the Maldive Islands. The baroclinic signals that originate from Abd al Kuri Island propagate meridionally, whereas those originating from the west coast of India propagate southwestward. The strength and energy flux of the internal tides in the Arabian Sea exhibit significant seasonal and spatial variability. The internal tides generated during winter are more energetic and can propagate further than those generated in summer. Doppler shifting and horizontal variations in stratification can explain the differences in the internal tides’ seasonal distributions.

Active transpression along the Owen oceanic transform fault, India - Somalia plate boundary

<p>The Owen oceanic transform fault is a 300-km long linear structure connecting the Carlsberg and Sheba spreading centers in the northwest Indian Ocean. It presently forms with the Carlsberg ridge the active plate boundary between India and Somalia. The Owen transform fault accommodates the left-lateral strike-slip motion between India and Somalia at a rate of about 23 mm/yr<strong>. </strong> Firstly identified by Tuzo Wilson in the 60s, this oceanic transform remains poorly described. The fault was recently surveyed in the Spring of 2019 during the VARUNA and CARLMAG cruises (https://doi.org/10.17600/18001108, https://doi.org/10.17600/18000872) along its entire length aboard BHO Beautemps-Beaupré, an oceanographic ship operated by the French Naval Hydrographic and Oceanographic Services (SHOM) and the French Navy.</p><p>During these missions a set of high-resolution seismic lines (>5000 km) were acquired together with high resolution multibeam bathymetry. The data cover both the active and fossil traces of the transform fault between 9°N and 15°N, at a place where continuous deposition of the distal Indus turbiditic sediments offers a unique high-resolution stratigraphic record of past regional tectonic events.</p><p>The new bathymetric mapping reveals two remarkable transpressive ridges on the active fault trace. A precise stratigraphic work using seismic profiles and drilling data of the ODP leg 117 allows the time calibration of the new seismic lines as far south as the Carlsberg ridge.</p><p>We show that a major compressive event occurred on the Owen Oceanic Transform Fault recently between 1.5 Ma and 2.4 Ma. Compression is still active today as evidenced by Sub-bottom profiler data (3.5 kHz) and two compressive focal mechanisms found in the historical seismicity records. At the intersection with the Carlsberg ridge, the southern transpressive ridge bends and stands ~1200 m above the seafloor at its apex, suggesting a maximum surrection rate near 800 m/Ma.  These new geophysical dataset combined with previous cruises offers an unprecedented window on the recent evolution of the India-Somalia plate boundary.</p>

Sulfurimonas indica sp. nov., a hydrogen- and sulfur-oxidizing chemolithoautotroph isolated from a hydrothermal sulfide chimney in the Northwest Indian Ocean

A novel mesophilic, hydrogen- and sulfur-oxidizing bacterium, designated strain NW8NT, was collected from a sulfide chimney at the deep-sea hydrothermal vent on the Carlsberg Ridge of the Northwest Indian Ocean. The cells were Gram-stain-negative, motile, short rods with a single polar flagellum. The temperature, pH and salinity ranges for growth of strain NW8NT were 4–40 °C (optimum, 33 °C), pH 4.5–7.5 (optimum, pH 5.5) and 340–680 mM NaCl (optimum, 510 mM). The isolate was an obligate chemolithoautotroph capable of growth using hydrogen, thiosulfate, sulfide or elemental sulphur as the sole energy source, carbon dioxide as the sole carbon source and molecular oxygen as the sole electron acceptor. The major cellular fatty acids of strain NW8NT were summed feature 3 (C16 : 1 ω7c and/or C16 : 1 ω6c), C16 : 0 and summed feature 8 (C18 : 1 ω7c and/or C18 : 1 ω6c). The total size of its genome was 2 093 492 bp and the genomic DNA G+C content was 36.9 mol%. Phylogenetic analysis based on 16S rRNA gene sequences and core genes showed that the novel isolate belonged to the genus Sulfurimonas and was most closely related to Sulfurimonas paralvinellae GO25T (97.4 % sequence identity). The average nucleotide identity and DNA–DNAhybridization values between strain NW8NT and S. paralvinellae GO25T was 77.8 and 21.1 %, respectively. Based on the phylogenetic, genomic and phenotypic data presented here, strain NW8NT represents a novel species of the genus Sulfurimonas , for which the name Sulfurimonas indica sp. nov. is proposed, with the type strain NW8NT (=MCCC 1A13988T=KTCC 15780T).