Ultrastructural and morphological characterization of Trypanosoma bubalisi reveals an active endocytic system

Trypanosoma bubalisi is a newly identified mammalian trypanosome isolated from a freshwater leech (Hirudinaria manillensis) and the water buffalo (Bubalus bubalis) is considered its host. Despite the detailed morphological description of in vitro cultivated forms of this trypanosome, little is known about its ultrastructure. In this study, a detailed ultrastructure of T. bubalisi was characterized using scanning electron microscopy, transmission electron microscopy and focused ion beam-scanning electron microscopy. Two membrane-bound organelles were identified, multivesicular body-like vesicles (ve1) and large lipid-rich vesicles resembling reservosomes (ve2), alongside an extracellular 'beads-on-a-string' structure. These all appear to be associated with endocytosis or secretion. Three-dimensional reconstructions confirmed the organization and distribution of the two membrane-bound organelles. Functional assays using Tomato lectin and Lyso-Tracker demonstrated that ve2 is involved in endocytic uptake and may act as a terminal storage compartment. Compared to the pathogen causing Nagana, Trypanosoma brucei, T. bubalisi showed higher endocytic activity under both 27 °C and 4 °C conditions. These findings suggest that T. bubalisi possesses an active endocytic system and may share conserved mechanisms of material transport and storage with the pathogen causing Chagas' disease, Tryponosoma cruzi.