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

Reservosomes are large membrane-bound structures found mainly at the p osterior 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) s pp. strains M431, M504, and M519 isolated from bats (Epitesicus sp.) i n 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 wa s carried out with the Y strain to follow the development of reservoso mes and lipid droplets during in vitro cultivation of the parasites. R eservosomes were partitioned to the daughter cells during cell divisio n such that the organelles were present in newly formed parasites. Est imation of the volume density after 3, 5, 7, 9, and 12 days of cultiva tion 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). Morph ological changes also occurred: type I reservosomes presented an elect ron-dense matrix with lipid droplets and were characteristic of younge r cultures, whereas type II reservosomes presented a homogeneous matri x without lipid inclusions and predominated in older cultures. These o rganelles were absent in bloodstream trypomastigote forms isolated fro m infected mice. Lipid inclusions were found in larger numbers at the 3rd and 12th days of culture, but their volume density was lower at th e log phase of growth.