Evolutionary Measurements Using Ribosomal Rna Sequence Comparisons (Phylogeny)
Yang, De-Cheng
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https://hdl.handle.net/2142/70608
Description
Title
Evolutionary Measurements Using Ribosomal Rna Sequence Comparisons (Phylogeny)
Author(s)
Yang, De-Cheng
Issue Date
1986
Department of Study
Plant Pathology
Discipline
Plant Pathology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Microbiology
Abstract
Comparisons of complete 16S ribosomal RNA sequences have been used to confirm and refine the phylogeny of bacteria. Two bacterial 16S rRNAs have been analysed in this study.
In the first chapter Agrobacterium tumefaciens was used to study mitochondrial origins. Analysis of cytochrome c sequences suggest the mitochondrion to have arisen from the purple bacterial "phylum". However, the gene for mitochondrial cytochrome c is not located in the mitochondrial genome, but in the nucleus, which makes this hypothesis somewhat questionable. The genes for rRNAs do reside in the mitochondrial genome. To find direct genetic evidence and further delimit the source of the endosymbiont(s), the A. tumefaciens 16S rRNA gene was cloned and sequenced. Its sequence was compared to those of the plant mitochondrion and various eubacteria and analysed in several ways to demonstrate phylogenetic relationships. The results confirm the conclusion suggested by cytochrome c sequence analysis and further indicate that the (alpha)-subdivision of the purple bacteria appears to be the source of the endosymbiont(s) that gave rise to the mitochondria.
In the second chapter Methanospirillum hungatei was used to study archaebacterial phylogeny. The archaebacteria comprise two major divisions, the methanogens and their relatives (extreme halophiles and the wall-less species Thermoplasma acidophilum) and the sulfur-dependent archaebacteria. Within the former cluster, the methanogens form three distinct subgroups and the halophiles another. Earlier studies were unable to resolve the relationship among the three groups (the Methanobacteriales, the Methanococcales, and the Methanomicrobiales) and the extreme halophiles. To resolve these relationships, the Ms. hungatei (order Methanomicrobiales) 16S rRNA gene was sequenced. Analysis shows that Methanomicrobiales is specifically related to the extreme halophiles, to the exclusion of the Methanococcales and Methanobacteriales.
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