The origin of life is a long-standing mystery which has puzzled many people. This mystery possesses not only philosophical, but also important biological significance. In order to unveil this mystery, first we can gain insight from the LUCA, that is, the Last Universal Common Ancestor, a hypothetical common ancestor to all the living organisms existing today. Our previous tRNA and aaRS paralogous gene studies congruously pointed to a Methanopyrus kandleri (Mka)-proximal LUCA. Further searches for organisms even closer to LUCA than Mka also may begin with members of Methanopyrus genus, or organisms that are close relatives of the Methanopyrus. Recently, the members of Methanopyrus were discovered within the Atlantic, Pacific and Indian Oceans. In this thesis, the usefulness of ValRS-IleR...[ Read more ]

The origin of life is a long-standing mystery which has puzzled many people. This mystery possesses not only philosophical, but also important biological significance. In order to unveil this mystery, first we can gain insight from the LUCA, that is, the Last Universal Common Ancestor, a hypothetical common ancestor to all the living organisms existing today. Our previous tRNA and aaRS paralogous gene studies congruously pointed to a Methanopyrus kandleri (Mka)-proximal LUCA. Further searches for organisms even closer to LUCA than Mka also may begin with members of Methanopyrus genus, or organisms that are close relatives of the Methanopyrus. Recently, the members of Methanopyrus were discovered within the Atlantic, Pacific and Indian Oceans. In this thesis, the usefulness of ValRS-IleRS interparalog distance as a probe was tested to assess the relative primitiveness of different Methanopyrus members originating from different oceans, and search for evidence for organisms even closer to LUCA than Mka. From the study, we observed that unlike either Pacific Ocean or Atlantic Ocean where only one Methanopyrus group has been discovered, two distinct Methanopyrus groups have been found in Indian Ocean pooled sample. Among the Methanopyrus isolates from the Atlantic and Pacific Oceans, Mka was identified to be closest to LUCA based on its highest ValRS-IleRS intraisolate identity. However, the Methanopyrus members from Indian group 2 showed an even higher VlaRS2-IleRS2 identity in matrix and therefore would be closer to LUCA than Mka. The Methanopyrus members from Indian Ocean group 1 would be farther away from LUCA than Mka based on their lower VlaRS1-IleRS1 identity in matrix. Thus, Indian Ocean group 2 was closest to LUCA; Pacific Ocean group and Indian Ocean group 1 shared a similar distance to LUCA; Atlantic group was the farthest away from LUCA. Therefore further studies on this archaea may shed new light on the origin of life.