What we can learn from the study of thermophilic archaea: From the common ancestor to the protoenkaryotic cell.
Akihiko Yamagishi
School of Life Science, Tokyo University of Pharmacy and Life Science, 1432-1 Horinouchi, Hachioji, Tokyo 192-0392 Japan
Phone: 0426-76-7139, Fax: 0426-76-7145, e-mail: yamagisi@LS.toyaku.ac.jp
The general phylogenetic tree constructed from 16SrRNA sequences has been widely accepted. Based on the composite phylogenetic tree of duplicated genes, root of the tree is placed in the eubacterial branch of the tree. Woese has pointed out the antiquity of thermophilic organisms. Several other authors have discussed the thermophilic origin of life and/or thermophilic common ancestor. However, the thermophilic origin of life is criticized by Millar based on unstability of biological compound. Thermophilic common ancestor is also criticized by Forrtere. Recently, Galtier et al. have estimated the G+C content of rRNA genes of the common ancestor and suggested the nonhyperthermophilic common ancestor. We have designed the experiments to test the thermophilic common ancestor hypothesis. The results will be presented.
Enkaryotic cells have complex cellular structures having membrane-surrounded organelles. Mitochondria and chloroplasts have endosymbiotic origin of proteobacterium and cyanobacterium, respectively. Nuclear and cytoplasmic portion of eukaryotic cells has originated from common ancestor with archaebacteria. We have found lamellar structures of cells in thermophilic archaeon Thermoplasma acidophilum. The implication of the structure will be discussed.
