THE RESERVOSOMES OF EPIMASTIGOTE FORMS OF TRYPANOSOMA-CRUZI - OCCURRENCE DURING IN-VITRO CULTIVATION

Reservosomes are large membrane-bound structures found mainly at the posterior end of epimastigote forms of Trypanosoma cruzi, the agent of Chagas' disease. We screened 5-day-old culture forms of the following strains at the ultrastructural level for the presence of reservosomes: T. cruzi strains Y and YuYu as well as Trypanosoma (Schizotrypanum) spp. strains M431, M504, and M519 isolated from bats (Epitesicus sp.) in Santa Catarina, Brazil. The organelles could be found in all strains analyzed, supporting a previous hypothesis that they are a marker of trypanosomes of the Schizotrypanum subgenus. Stereological analysis was carried out with the Y strain to follow the development of reservosomes and lipid droplets during in vitro cultivation of the parasites. Reservosomes were partitioned to the daughter cells during cell division such that the organelles were present in newly formed parasites. Estimation of the volume density after 3, 5, 7, 9, and 12 days of cultivation showed that it was lower in younger cultures, becoming maximal at day 9 (8.0%), but decreased in older cultures (5.9% at day 12). Morphological changes also occurred: type I reservosomes presented an electron-dense matrix with lipid droplets and were characteristic of younger cultures, whereas type II reservosomes presented a homogeneous matrix without lipid inclusions and predominated in older cultures. These organelles were absent in bloodstream trypomastigote forms isolated from infected mice. Lipid inclusions were found in larger numbers at the 3rd and 12th days of culture, but their volume density was lower at the log phase of growth.