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RESEARCH PRODUCT

Transition from Protozoa to Metazoa: An Experimental Approach

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Until recently, stromatolites were thought to be the oldest fossils on earth that were very abundant 2000 to 3000 Ma (million years) ago (Walter 1994). Recently, the biological origin of these fossils has been questioned (Walter 1996). The universal phylogenetic tree exhibits a tripartite division of the living world into Bacteria (“eubacterial”), Archaea (“archebacterial”), and Eucarya [“eukaryotic” (Woese 1987; Woese et al. 1991)]. Based on comparisons of amino acid (aa) sequence data from enzymes, it has been proposed that the common ancestor of prokaryotes and eukaryotes lived about 2000 Ma ago (Doolittle et al. 1996). Phylogenetic analysis of the 70kDa heat-shock proteins suggested that the first eukaryotic cell was a fusion product of a member of the Archaebacteria with a Gram-negative bacterium. Later in evolution a purple proteobacterium and a cyanobacterium invaded eukaryotic cells and gave rise to mitochondria and chloroplasts (Gupta and Singh 1994).