PHYLOGENETIC-RELATIONSHIPS AMONGST THE HYPERTHERMOPHILIC ARCHAEA DETERMINED FROM PARTIAL 23S RIBOSOMAL-RNA GENE-SEQUENCES

Large sections of the 23S rRNA genes of five hyperthermophiles Pyrobaculum islandicum, Pyrobaculum organotrophum, Pyrococcus furiosus, Pyrodictium occultum and Staphylothermus marinus were cloned and sequenced. The sequenced regions correspond to domains II to VI of the rRNA and only the 5'-region is lacking. They were aligned and compared with other archaeal 23S rRNA sequences. Two introns were located in the single gene of Pyrobaculum organotrophum but none were found in that of the closely related Pyrobaculum islandicum. The relevance of this result to the recent history of the archaeal rRNA introns is considered. A phylogenetic tree of the hyperthermophilic archaea is derived from the sequence alignments using the sequence of the extremely thermophilic bacterium Thermatoga maritima to define an outgroup.