Phylogenetic tree highlighting the position of S. hellenicus relative to the type strains of the other species within the order Desulfurococcales. The tree was inferred from 1,333 aligned characters [4,5] of the 16S rRNA gene sequence under the maximum likelihood (ML) criterion . Rooting was done initially using the midpoint method  and then checked for its agreement with the current classification (Table 1). The branches are scaled in terms of the expected number of substitutions per site. Numbers adjacent to the branches are support values from 1,000 ML bootstrap replicates  (left) and from 1,000 maximum parsimony bootstrap replicates  (right) if larger than 60%. Lineages with type strain genome sequencing projects registered in GOLD  are labeled with one asterisk, those listed as ‘Complete and Published’ with two asterisks.