Thermococcus gorgonarius sp. nov. and Thermococcus pacificus sp. nov.: heterotrophic extremely thermophilic archaea from New Zealand submarine hot vents

Abstract

Two extremely thermophilic archaea, designated W-12 and P-4, were isolated from a geothermal vent in the tidal zone of Whale Island, New Zealand, and from geothermally heated bottom deposits of the Bay of Plenty, New Zealand, respectively. Cells of isolate W-12 are irregular cocci, 0·3--1·2 pm in diameter, motile with polar flagella. The cell envelope consists of one layer of subunits with a major protein of M_r 75000. Cells produce protrusions of different kinds: prostheca-like, chains of bubbles, or network of fimbriae. Cells of isolate P-4 are regular cocci, 0·7--1·0 μm in diameter, motile with polar flagella. The cell envelope consists of two layers of subunits; its major protein has an M_r of 56000. Both organisms are obligate anaerobes, fermenting peptides in the case of strain W-12, or peptides and starch in the case of P-4. Elemental sulfur is required for growth and is reduced to hydrogen sulfide. The optimal growth temperature of the new isolates is in the range 80-88 °C. The optimal growth pH is 6·5--7·2. The G+C content of the DNA of strain W-12 is 50·6 mol%, and of strain P-4 is 53·3 mol%. Based on physiological characteristics, 16S rDNA sequence comparison and DNA base composition, the new isolates were considered to be members of the genus Thermococcus. The low level of DNA-DNA hybridization with the type strains of other Thermococcus species confirms the novel species status of the new isolates. The new isolates are described as Thermococcus gorgonarius sp. nov., with type strain W-12 (= DSM 10395^T), and Thermococcus pacificus sp. nov., with type strain P-4 (= DSM 10394^T).