Pyrococcus woesei, sp. nov., an ultra-thermophilic marine archaebacterium, representing a novel order, Thermococcales

The anaerobic sulfur-reducing marine archaebacterium Pyrococcus woesei is an "ultra-thermophile" growing optimally between 100 and 103°C at pH 6 to 6.5 and 30 g/l NaCl. Growth proceeds, on solid supports or in suspension, by sulfur respiration of yeast extract or peptides, on yeast extract also without S ^o in the presence of H ₂, or on polysaccharides in the presence of H ₂ and S ^o. The generation time was as low as 35 minutes either on solid supports or in suspension. The cells have a roughly spherical, often elongated and constricted appearance, similar to Thermococcus celer. Frequently, they occur as diploforms. Cells grown on solid supports have dense tufts of flagellae or pili attached to one pole. When P. woesei was grown by sulfur respiration on yeast extract or bactotryptone in the presence of starch, complete lysis occurred after the peak of cell density had been reached. Concomitantly icosaedric particles of about 30 nm in diameter were liberated which showed a defined simple protein composition. P. woesei belongs to the Thermococcaceae as indicated by the immunochemical cross-reaction of its DNA-dependent RNA polymerase with the polymerases of T. celer and the isolate AN1 from New Zealand. Quantitative analysis of its phylogenetic position by DNA-rRNA cross-hybridization places it at the end of a long branch of the Thermococcaceae, whereas the isolate AN1 is on a branch of intermediate length and T. celer on an extremely short branch. The phylogenetic depth of this group and its clear separation from the neighbouring Thermoproteales and Methanococcales call for the introduction of a separate order: Thermococcales, which represents a third major division of the archaebacteria between the Thermoproteales + Sulfolobales and the methanogens + halophiles.