Figure 1.

Phylogenetic tree of the known Pyrobaculum species based on 16S ribosomal RNA sequence. Accession numbers and associated culture collection identifiers (when available) for 16S ribosomal RNA genes are: Pyrobaculum aerophilum (NC_003364.1, DSM 7523); P. calidifontis (NC_009073.1, DSM 21063); P. islandicum (NC_008701.1, DSM 4184); P. arsenaticum (NC_009376.1, DSM 13514); P. oguniense (CP003316, DSM 13380); Thermoproteus neutrophilus (NC_010525.1, DSM 2338); P. sp. 1860 (CP003098.1); P. organotrophum (AB304846.1, DSM 4185); P. sp. CBA1503 (HM594679.1); P. sp. M0H (AB302407.1); P. sp. AQ1.S2 (DQ778007.1); P.WIJ3 (AJ277125.1); ‘P. neutrophilum’ (X81886). Sequences were aligned using MAFFT v.6 [8], followed by manual curation [9] to remove 16S ribosomal introns and all terminal gap columns caused by missing sequence. The maximum likelihood tree was constructed using Tree-Puzzle v. 5.2 [10] using exact parameter estimates, 10,000 quartets and 1000 puzzling steps. Thermoproteus tenax Kra1 (NC_016070.1, DSM 2078) was included as an outgroup. Numbered branches show bootstrap percentages and branch lengths depict nucleotide mutation rate (see scale bar upper right).