Trypanosomes (phylum Euglenozoa, genus Kinetoplastida) infect a wide variety of vertebrates including human. Euglenozoa is classified into three general groups ; heterotrophic form, flee-living form and parasitic form. Kinetoplastida includes various parasitic flagellates. Interestingly, no parasitic form is known in Euglenozoa except the class Kinetoplastida. Therefore, Kinetoplastida are considered to acquired parasitic ability after divergence of genus Kinetoplastida and other lineages. In this study, I focused on the horizontal gene transfer (HGT) events of ancient trypanosomes because HGT is a major driving force to increase evolvability. To identify horizontally transferred genes in trypanosomes, I comprehensively analyzed DNA-sequences data. Firstly, I compared whole genes of T. cruzi or T. brucei and whole genome of 2, 504 prokaryote species, thereby obtained trypanosome genes conserved in prokaryotes. Secondly, I selected HGT candidates by eliminating inherited and duplicated genes. As a result, T. brucei and T. cruzi is predicted to possess 63 and 72 HGT genes, respectively from various donor prokaryotes strains belong to a wide of phylum, such as Firmicutes, Bacteroidetes and Proteobacteria. Finally, I identified HGT candidates which evolutionary processes were strongly suggested by phylogenetic analysis. Consequently, I defined trans-Sialidase and DNA repair protein as strong HGT candidates. These enzymes play a central role for evasion of host's immune system, suggesting that HGT events had encouraged the development of parasitic abilities of trypanosomes. I hope that this study contributes to deeper understanding of infectious diseases caused by protozoa and the drug discovery of trypanosomiasis.
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