Reevaluation of the phylogenetic depth of the marine aerobic hyperthermophilic archaeon Aeropyrum pernix based on comparative analysis of 23S rRNA sequences

Aeropyrum pernix, a strictly aerobic marine hyperthermophilic archaeon, has been studied as a potential biotechnological source. In order to clarify t he phylogenetic position of A. pernix, the nearly complete nucleotide seque nce of the 23S rRNA was determined and compared with the other hitherto kno wn archaeal counterparts. To avoid the artifact caused by disparities of G + C content, transversion evolutionary distance analysis was adopted. The r esult confirmed that A. pernix is closely allied to the Pyrodictium-Desulfu rococcus-Staphylothermus group (the order "Igneococcales") within the kingd om Crenarchaeota. However, it also revealed that the genus Aeropyrum diverg es sharply from the other genera within the family Desulfurococcaceae. Thus , we concluded that the decision to transfer the genus Aeropyrum from the f amily Desulfurococcaceae is reasonable in light of our present data, as wel l as the physiological characteristics of this archaeon reported previously .