FIG. 3.

Distance tree showing the positions of 21 Thermococcus and Pyrococcus isolates and 30 reference strains. The sequences of T. aggregans (accession no. Y08384), T. alcaliphilus (AB055121), T. kodakaraensis KOD1 (D38650), T. sibiricus (AJ238992), T. sulfurophilus OGL-20P (AF394925), T. zilligii (U76534), and P. furiosus (U20163) were obtained from the GenBank database. The tree was constructed by using the neighbor-joining method (31) included in the GeneBase program (Applied-Maths). Phylogenetic distances were calculated based on 1,225 nucleotides of the 16S rRNA gene sequences (E. coli 16S rRNA gene positions 115 to 1365). Bootstrap values, expressed as percentages of 1,000 data sets, are indicated at the branch points. Only values higher than 60% are shown. Scale bar = 1 nucleotide substitution per 100 nucleotides. A superscript a indicates a species whose name has not been validly published.