The Nucleotide Sequence of the 16S rRNA Gene and Flanking Regions from Methanobacterium formicicum: The Phylogenetic Relationship between Methanogenic and Halophilic Archaebacteria

Abstract

Summary By blot hybridization experiments it was demonstrated that Methanobacterium formicicum possesses two putative rDNA transcriptional units of the eubacterial type (5′-16S-tRNA Ala -23S-5S-3′). Fragments of each unit which contain the 16S rRNA gene plus flanking regions were cloned and their nucleotide sequences determined. The 16S rRNA encoding sequence was compared to the respective sequences of Methanococcus vannielii, Halobacterium volcanii, Halobacterium cutirubrum and Halococcus morrhuae . The following results were obtained: (i) The three halophiles share an equal evolutionary distance; (ii) the Methanococcus and Methanobacterium sequences are more closely related than previously indicated by the S AB values; the evolutionary distance between Methanobacterium and the halophile sequences is less than the one exhibited by the Methanococcus structure; (iii) the evolutionary rates of the sequences are quite different; the Methanobacterium formicium sequence exhibits an evolutionary rate somewhat lower than the Methanococcus structure and is drastically different from the high genetic drift of the halophile small subunit rRNA's.