The parabasal filaments of Trichomonas vaginalis: A new filament and observations using 0.8 nm-resolution scanning electron microscopy

Trichomonas vaginalis is the etiologic agent of trichomoniasis, the most common nonviral sexually transmitted infection worldwide, with an estimated 260 million new cases annually. T. vaginalis contains organelles common to all eukaryotic cells, uncommon cell structures such as hydrogenosomes, and a complex and elaborate cytoskeleton constituting the mastigont system. The mastigont system is mainly formed by several proteinaceous structures associated with basal bodies, the pelta-axostylar complex made of microtubules, and striated filaments named the costa and the parabasal filaments (PFs). Although the structural organization of trichomonad cytoskeletons has been analyzed using several techniques, observation using a new generation of scanning electron microscopes with a resolution exceeding 1 nm has allowed more detailed visualization of the three-dimensional organization of the mastigont system. In this study, we have investigated the cytoskeleton of T. vaginalis using a diverse range of scanning probe microscopy techniques, which were complemented by electron tomography and Fast-Fourier methods. This multi-modal approach has allowed us to characterize an unknown parabasal filament and reveal the ultrastructure of other striated fibers that have not been published before. Here, we show the differences in origin, striation pattern, size, localization, and additional details of the PFs, thus improving the knowledge of the cell biology of this parasite.