Descent of Bacteria and Eukarya from an archaeal root of life

Abstract

The three biological domains delineated based on SSU rRNAs are confronted by uncertainties regarding the relationship between Archaea and Bacteria, and the origin of Eukarya. Herein the homologies between the paralogous valyl-tRNA and isoleucyl-tRNA synthetases in a wide spectrum of species revealed vertical gene transmission from an archaeal root of life through a Primitive Archaea Cluster to an Ancestral Bacteria Cluster of species. The higher homologies of the ribosomal proteins (rProts) of eukaryotic Giardia toward archaeal relative to bacterial rProts established that an archaeal-parent rather than a bacterial-parent underwent genome merger with an alphaproteobacterium to generate Eukarya. Moreover, based on the top-ranked homology of the proteins of Aciduliprofundum among archaea toward the Giardia and Trichomonas proteomes and the pyruvate phosphate dikinase of Giardia, together with their active acquisition of exogenous bacterial genes plausibly through foodchain gene adoption, the Aciduliprofundum archaea were identified as leading candidates for the archaeal-parent of Eukarya.