Thermococcus siculi sp. nov., a Novel Hyperthermophilic Archaeon Isolated from a Deep-Sea Hydrothermal Vent at the Mid-Okinawa Trough
Ralf GROTE*a, Lina LIb, Jin TAMAOKAb, Chiaki KATOb, Koki HORIKOSHIb, and Garabed ANTRANIKIANa
a Department of Technical Microbiology, Technical University Hamburg -Harburg, Denickestrasse 15, D-21071 Hamburg, Germany
b The DEEPSTAR Group, Japan Marine Science and Technology Center, 2-15 Natsushima- cho, Yokosuka 237, Japan
Hyperthermophilic bacteria and archaea (temperature optimum > 80℃) have attracted the attention of researchers due to their evolutionary significance, their ability to maintain their cellular integrity even at most inhospitable temperatures, and their biotechnological potential. These hyperthermophiles have been mainly isolated from terrestrial and shallow marine environments (1). As a result of the progress in deep-sea exploration systems, an increasing number of hyperthermophilic archaea has been isolated recently from eco-systems located in the deep-sea (2).
A novel coccoid-shaped, hyperthermophilic, anaerobic archaeon, strain RG-20, was isolated from a deep-sea hydrothermal vent fluid sample taken at 1,394 m depth at the Mid-Okinawa Trough (27°32.7'N, 126°58.5'E) by employing the manned submersible "Shinkai 2000". Cells of this isolate occur singly or in pairs and are about 0.8 to 2μm in diameter as determined by phase-contrast microscopy. Growth was observed over a broad temperature range, namely between 50 and 93℃ with an optimum at 85℃. The pH-range for growth was 5.0 to 9.0, with an optimum around 7.0. Strain RG-20 requires 1 to 5% of NaCl for growth and cell lysis was observed at concentrations below 1%. The newly isolated strain grows preferentially in the presence of elemental sulfur on proteinaceous substrates such as yeast extract, peptone or tryprone, but no growth was observed on pyruvate, lipids or carbohydrates including starch, xylan and pullulan. This microorganism is resistant to streptomycin, chloramphenicol, ampicillin and kanamycin at concentrations up to 150 μg/ml, but was susceptible to rifampicin. Thin-layer chromatography (TLC) examinations of the hydrolyzed core lipids revealed the presence of archaeol and caldarchaeol. The mol% G+C content of the DNA is 55.8. Partial sequencing of the 16S rDNA indicates that strain RG-20 belongs to the genus Thermococcus. Considering these data and based on the results from DNA-DNA hybridization studies covering five different Thermococcus and one Pyrococcus species, we propose that this microorganism should be classified as a new species named Thermococcus siculi.
1. Stetter, K.O. (1996) FEMS Microbiol. Rev., 18, 149-158.
2. Tunnicliffe, V. (1991) Oceanogr. Mar. Biol. Annu. Rev., 29, 319-407.
