A possible mitochondrial gene in the early-branching amitochondriate protist Trichomonas vaginalis - PubMed (original) (raw)

A possible mitochondrial gene in the early-branching amitochondriate protist Trichomonas vaginalis

A J Roger et al. Proc Natl Acad Sci U S A. 1996.

Abstract

Trichomonads are anaerobic flagellated protists that, based on analyses of ribosomal RNA sequences, represent one of the earliest branching lineages among the eukaryotes. The absence of mitochondria in these organisms coupled with their deep phylogenetic position has prompted several authors to suggest that trichomonads, along with other deeply-branching amitochondriate protist groups, diverged from the main eukaryotic lineage prior to the endosymbiotic origin of mitochondria. In this report we describe the presence of a gene in Trichomonas vaginalis specifically related to mitochondrial chaperonin 60 (cpn60). A recent study indicates that a protein immunologically related to cpn60 is located in trichomonad hydrogenosomes. Together, these data provide evidence that ancestors of trichomonads perhaps harbored the endosymbiotic progenitors of mitochondria, but that these evolved into hydrogenosomes early in trichomonad evolution.

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Figures

Figure 1

Figure 1

Phylogenies of cpn60 homologs. Sequences were selected from the database for organisms previously shown to branch in the region of the mitochondrial cpn60 clade (11, 12). The trees shown are derived from neighbor-joining analysis of a accepted point mutation corrected distance matrix. Percentage bootstrap support is shown above selected branches in boxes, from bootstrap analyses employing the protein maximum likelihood (ML), neighbor-joining distance (NJ), and maximum parsimony (MP) methods. (A) Cpn60 tree derived from the full alignment. The maximum likelihood tree (ln likelihood = −8933.6) differed from the neighbor-joining tree by the placement of the T. vaginalis and E. histolytica sequences as sister groups. Parsimony generated five trees of length = 2369 all of which differed principally from the tree shown by the placement of T. vaginalis as a sister group of the Rickettsiales species. Asterisks (∗) indicate that the method used did not recover this node in the majority of bootstrap replicates. (B) Cpn60 tree with the E. histolytica sequence excluded. Maximum likelihood yielded a tree of identical topology (ln likelihood = −12181.7), while parsimony generated three trees of length = 2209. Two of these differed from the neighbor-joining tree by the placement of the α-Protebacteria (excluding the Rickettsiales) as a sister group to the γ- and β-Proteobacteria. The third differed by placing T. vaginalis as an immediate relative to the Rickettsiales (see_Results_).

Figure 2

Figure 2

The impact of the sampling of Rickettsiales species on the bootstrap support for two alternative topologies of the cpn60 tree. The dataset excluding the E. histolytica sequence, was used to examine the bootstrap support for two alternative clades each indicated by • on the two trees. (A) The T. vaginalis/mitochondria clade found by neighbor-joining, maximum likelihood and two of the three maximum parsimony trees. (B) The T. vaginalis/Rickettsiales clade displayed by the third maximum parsimony tree (see Materials and Methods). Percentage bootstrap support for each clade is indicated to the left of the trees. Three different combinations of Rickettsiales species were used in the dataset. Species abbreviations are: Ec, Ehrlichia chaffeensis; Cr, C. ruminantium and Rt;R. tsutsugamushi. For each combination of species, bootstrap support for the clade was evaluated using the methods NJ (neighbor-joining distance), MP (maximum parsimony) and ML (protein maximum likelihood) as described in the Materials and Methods.

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