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Archaebacterial phylogeny: perspectives on the urkingdoms.
1Department of Genetics and Development, University of Illinois, Urbana 61801, USA.
Systematic and Applied Microbiology
|January 1, 1986
Summary
Archaebacterial phylogeny, based on 16S ribosomal RNA sequences, reveals two main divisions: sulfur-dependent thermophiles and methanogens with relatives. This classification confirms archaebacteria as a distinct evolutionary lineage.
Area of Science:
- Microbiology
- Evolutionary Biology
- Molecular Biology
Background:
- Archaebacterial phylogeny has been historically challenging to define.
- Earlier classifications relied on phenotypic data, leading to ambiguities.
Purpose of the Study:
- To refine and extend the understanding of archaebacterial phylogeny.
- To establish a robust classification based on molecular sequence data.
Main Methods:
- Comparative analysis of complete 16S ribosomal RNA (rRNA) gene sequences.
- Phylogenetic reconstruction and analysis of sequence divergence.
Main Results:
- Archaebacteria resolve into two primary phylogenetic divisions: sulfur-dependent thermophiles (Division I) and methanogens/relatives (Division II).
- Division I is phenotypically and phylogenetically coherent, including genera like Sulfolobus and Thermoproteus.
- Division II is more diverse, encompassing methanogens, extreme halophiles, and thermoacidophiles, with Thermococcus celer potentially representing a third division.
- Extreme halophiles show a specific relationship to Methanomicrobiales within Division II.
- 16S rRNA sequence data strongly supports archaebacteria as a distinct clade, separate from eubacteria and eukaryotes.
Conclusions:
- 16S rRNA sequence analysis provides a reliable framework for archaebacterial classification.
- The proposed two-division system refines existing concepts and resolves taxonomic uncertainties.
- Alternative phylogenetic proposals lacking sequence evidence are critically evaluated and found wanting.