16S rDNA-based phylogeny of the archaeal order Sulfolobales and reclassification of Desulfurolobus ambivalens as Acidianus ambivalens comb nov

A 16S rDNA-based phylogenetic analysis of 12 thermoacidophilic members of Archaea demonstrates the Sulfolobales to be a monophyletic group within the Crenarchaeota. Several phylogenetic clusters are evident, sometimes not in agreement with the present taxonomic ranking. The four Sulfolobus species, represent three well separated branches. Further taxonomic features suitable to distinguish these groups are so far lacking, however. Therefore, a description of higher ranks appears not to be useful at present. The same is true for Acidianus brierleyi, which is clearly separated from the type species Acidianus infernus. On the other hand, Desulfurolobus ambivalens appears as a close relative of Acidianus infernus and, therefore does not represent a different genus. In line with its other physiological and biochemical similarities we assign Desulfurolobus ambivalens to the genus Acidianus as Acidianus ambivalens comb. nov. (type strain DSM 3772).