Close evolutionary relatedness of archaebacteria, Methanococcus and Halobacterium, to eukaryotes demonstrated by composite phylogenetic trees of elongation factors EF-Tu and EF-G: Eocyte tree is unlikely

Abstract

From a comparison of elongation factors Tu(EF-Tu) and G(EF-G) from a variety of species covering all the three urkingdoms (eubacteria, archaebacteria, and eukaryotes), including two archaebacterial species, Methanococcus vanielli, a methanogen, and Halobacterium halobium, an extremely holophilic archaebacterium, a rooted phylogenetic tree was inferred by the neighbor joining method and the maximum likelihood method, and the phylogenetic relationship among the three urkingdoms was determined. Furthermore the branching patterns of the three urkingdoms were examined in detail by the bootstrap resampling analysis. It was shown that both the extremely halophilic archaebacterium and the methanogen are more closely related to eukaryotes than they are to eubacteria with significant reliability. Thus the eocyte tree proposed by Lake et al. is highly unlikely: According to the eoeyte tree, the two archaebacterial groups should be closely related to eubacteria and distantly related to eukaryotes.