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|Title:||Phylogenetic Relationships of Thermophilic Bacteria|
|Department / Program:||Biology|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Abstract:||There are two lines of prokaryotic descent--the eubacteria and the archaebacteria. The phylogenetic relationships of several new isolates of extremely thermophilic bacteria have been determined and used to gain a deeper understanding of the role of thermophilic bacteria in early evolution. The 16S and 23S ribosomal RNA genes from the new bacterial isolates were cloned and sequenced. Several types of analysis on the sequences were used to place these extreme thermophiles in the phylogenetic trees of the eubacterial or archaebacterial kingdoms.
Thermotoga maritima is an unusual eubacterium which is capable of sustaining growth at temperatures up to 90$\sp\circ$C and which contains lipids of unique composition. Thermotoga maritima is a slowly evolving lineage and represents the deepest known branching in the eubacterial kingdom.
Thermococcus celer is phenotypically a typical sulfur-dependent archaebacteria. However, Thermococcus celer does not group phylogenetically with its phenotypic counterparts, but rather is the deepest known branching of the methanogen-halophile side of the archaebacterial phylogenetic tree.
Archaeoglobus fulgidus is an archaebacterium of novel phenotype--it is the only archaebacterium known to metabolize sulfur by dissimilatory sulfate reduction and it contains pure factor 420 and produces trace amounts of methane even though it is lacking some of the coenzymes normally required for methanogenesis. The phylogenetic position of Archaeoglobus fulgidus in the archaebacterial tree places it between Thermococcus celer and the deepest branching methanogen, Methanococcus vannielii. The phylogenetic evidence supports the interpretation that Archaeoglobus fulgidus represents a transition stage between a sulfur-based metabolism and methanogenesis.
Acidianus infernus is an archaebacterium which is capable of utilizing sulfur in two ways: aerobically by the oxidation of elemental sulfur or strictly anaerobically by sulfur reduction. The sequence data groups Acidianus infernus with the genus Sulfolobus on the sulfur-dependent branch of the archaebacterial tree.
The present phylogenetic evidence suggests that the ancestor of the archaebacteria and the eubacteria was thermophilic. Extreme thermophiles represent the deepest branches of both prokaryotic kingdoms, and these deep-branching lineages are slowly evolving. Further investigation of extremely thermophilic bacteria will be pivotal in addressing the nature of the common ancestor and the thermophilic ancestry of prokaryotes.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1988.
|Date Available in IDEALS:||2015-05-14|