Draft genome sequence of the sexually transmitted pathogen Trichomonas vaginalis

Abstract

We describe the genome sequence of the protist Trichomonas vaginalis, a sexually transmitted human pathogen. Repeats and transposable elements comprise about two-thirds of the approximately 160-megabase genome, reflecting a recent massive expansion of genetic material. This expansion, in conjunction with the shaping of metabolic pathways that likely transpired through lateral gene transfer from bacteria, and amplification of specific gene families implicated in pathogenesis and phagocytosis of host proteins may exemplify adaptations of the parasite during its transition to a urogenital environment. The genome sequence predicts previously unknown functions for the hydrogenosome, which support a common evolutionary origin of this unusual organelle with mitochondria.

Fig. 1

Karyotype and fluorescent in situ hybridization (FISH) analysis of T. vaginalis chromosomes. (A) Metaphase chromosome squashes of T. vaginalis reveal six chromosomes (I to VI). (B) FISH analysis using an 18S rDNA probe shows that all ~250 rDNA units localize to a single chromosome. (C) In contrast, the Tvmar1 transposable element (8) is dispersed throughout the genome.

Fig. 2

Schematic of T. vaginalis amino acid metabolism. A complete description of enzymatic reactions (represented as numbers) is given in the SOM text. Broken lines represent enzymes for which no gene was identified in the genome sequence, although the activity would appear to be required. Green boxes indicate enzymes encoded by candidate LGT genes.

Fig. 3

Structural organization of putative T. vaginalis surface molecules involved in host cell adherence and cyto-toxicity (28). Candidate surface protein families (a to f) are depicted as part of the glycocalyx (gray shading), known to be composed of LPG (g). The number of proteins with an inferred transmembrane domain (red box) is indicated at right, with the size of the entire family shown in parentheses. Substantial length variation exists between and within families (proteins are not drawn to scale). Additional information can be found in table S18.