A hyperthermophilic, strictly anaerobic archaeon, designated strain SY113^T, was isolated from a deep-sea hydrothermal vent chimney on the Southwest Indian Ridge at a water depth of 2770 m. Enrichment and isolation of strain SY113^Twere performed at 85 °C at 0.1 MPa. Cells of strain SY113^Twere irregular motile cocci with peritrichous flagella and generally 0.8–2.4 µm in diameter. Growth was observed at temperatures between 50 and 90 °C (optimum at 85 °C) and under hydrostatic pressures of 0.1–60 MPa (optimum, 27 MPa). Cells of SY113^Tgrew at pH 4.0–9.0 (optimum, pH 5.5) and a NaCl concentration of 0.5–5.5 % (w/v; optimum concentration, 3.0 % NaCl). Strain SY113^Twas an anaerobic chemoorganoheterotroph and grew on complex proteinaceous substrates such as yeast extract and tryptone, as well as on maltose and starch. Elemental sulphur stimulated growth, but not obligatory for its growth. The G+C content of the genomic DNA was 55.0 mol%. Phylogenetic analysis of the 16S rRNA sequence of strain SY113^Tshowed that the novel isolate belonged to the genusThermococcus. On the basis of physiological characteristics, average nucleotide identity values andin silicoDNA–DNA hybridization results, we propose a novel species, namedThermococcus aciditoleranssp. nov. The type strain is SY113^T(=MCCC 1K04190^T=JCM 39083^T).

A novel moderately thermophilic, anaerobic, heterotrophic bacterium (strain SY095^T) was isolated from a hydrothermal vent chimney located on the Southwest Indian Ridge at a depth of 2730 m. Cells were Gram-stain-positive, motile, straight to slightly curved rods forming terminal endospores. SY095^Twas grown at 45–60 °C (optimum 50–55 °C), pH 6.0–7.5 (optimum 7.0), and in a salinity of 1–4.5 % (w/v) NaCl (optimum 2.5 %). Substrates utilized by SY095^Tincluded fructose, glucose, maltose,N-acetyl glucosamine and tryptone. Casamino acid and amino acids (glutamate, glutamine, lysine, methionine, serine and histidine) were also utilized. The main end products from glucose fermentation were acetate, H₂and CO₂. Elemental sulphur, sulphate, thiosulphate, sulphite, fumarate, nitrate, nitrite and Fe(III) were not used as terminal electron acceptors. The predominant cellular fatty acids were C_14 : 0(60.5%) and C_16 : 0(7.6 %). The main polar lipids consisted of diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, five unidentified phospholipids and two unidentified aminophospholipids. No respiratory quinones were detected. The chromosomal DNA G+C content was 30.8 mol%. The results of phylogenetic analysis of the 16S rRNA gene sequences indicated that SY095^Twas closely related toCrassaminicella profundaRa1766H^T(95.8 % 16S rRNA gene sequence identity). SY095^Texhibited 78.1 % average nucleotide identity (ANI) toC. profundaRa1766H^T. Thein silicoDNA–DNA hybridization (DDH) value indicated that SY095^Tshared 22.7 % DNA relatedness withC. profundaRa1766H^T. On the basis of its phenotypic, genotypic and phylogenetic characteristics, SY095^Tis suggested to represent a novel species of the genusCrassaminicella, for which the nameCrassaminicella thermophilasp. nov. is proposed. The type strain is SY095^T(=JCM 34213=MCCC 1K04191). An emended description of the genusCrassaminicellais also proposed.

Bioluminescence is a common phenomenon in nature, especially in the deep ocean. The physiological role of bacterial bioluminescence involves protection against oxidative and UV stresses. Yet, it remains unclear if bioluminescence contributes to deep-sea bacterial adaptation to high hydrostatic pressure (HHP). In this study, we constructed a non-luminescent mutant of ΔluxA and its complementary strain c-ΔluxA of Photobacterium phosphoreum ANT-2200, a deep-sea piezophilic bioluminescent bacterium. The wild-type strain, mutant and complementary strain were compared from aspects of pressure tolerance, intracellular reactive oxygen species (ROS) level and expression of ROS-scavenging enzymes. The results showed that, despite similar growth profiles, HHP induced the accumulation of intracellular ROS and up-regulated the expression of ROS-scavenging enzymes such as dyp, katE and katG, specifically in the non-luminescent mutant. Collectively, our results suggested that bioluminescence functions as the primary antioxidant system in strain ANT-2200, in addition to the well-known ROS-scavenging enzymes. Bioluminescence contributes to bacterial adaptation to the deep-sea environment by coping with oxidative stress generated from HHP. These results further expanded our understanding of the physiological significance of bioluminescence as well as a novel strategy for microbial adaptation to a deep-sea environment.