Diversification of the microtubule system in the early stage of eukaryote evolution: Elongation factor 1 alpha and alpha-tubulin protein phylogeny oftermite symbiotic oxymonad and hypermastigote protists

The symbiotic protists of the lower termite have been regarded as a model o f early-branched eukaryotes because of their simple cellular systems and mo rphological features. However, cultivation of these symbiotic protists is v ery difficult. For this reason, these interesting protists have not been we ll characterized in terms of their molecular biology. In research on these organisms which have not yet been cultivated, we developed a method for ret rieving specific genes from a small number of cells, through micromanipulat ion without axenic cultivation, and we obtained EF-1 alpha and alpha -tubul in genes from members of the Hypermastigida-the parabasalid protist Trichon ympha agilis and the oxymonad protists Pyrsonympha grandis and Dinenympha e xilis-from the termite Reticulitermes speratus gut community. Results of ph ylogenetic analysis of the amino acid sequences of both proteins, EF-1 alph a and alpha -tubulin, indicate that the hypermastigid, parabasalid, and oxy monad protists do not share a close common ancestor. In addition, although the EF-1 alpha phylogeny indicates that these two groups of protists branch ed at an early stage of eukaryotic evolution, the alpha -tubulin phylogeny indicates that these protists can be assigned to two diversified clades. As shown in a recent investigation of alpha -tubulin phylogeny, eukaryotic or ganisms can be divided into three classes: an animal-parabasalids clade, a plant-protists clade, and the diplomonads. In this study, we show that para basalids, including hypermastigids, can be classified as belonging to the a nimal-parabasalids clade and the early-branching eukaryote oxymonads can be classified as belonging to the plant-protists clade. Our findings suggest that these protists have a cellular microtubule system that has diverged co nsiderably, and it seems that such divergence of the microtubule system occ urred in the earliest stage of eukaryotic evolution.