A quantitative ultrastructural study on the transformation of Trypanosoma brucei metacyclic to bloodstream forms in vitro.

The transformation of metacyclic to bloodstream forms of Trypanosoma brucei brucei was studied in vitro using light and electron microscopy. The ultrastructural composition was investigated with stereological methods and the mean cell volume determined in a Coulter Channelyzer. The mitochondrion showed the most significant changes during transformation with a reduction in volume as well as in the membrane areas. The glycosomes remained unchanged whereas the lipid inclusions increased over the 24 h incubation period. The metacyclic forms contained many vesicles in the reservoir vicinity with surface coat-like material on the inner side of the membrane. Metacyclic forms also contained a previously undescribed structure, termed "inclusion body". These large, polymorphic structures whose function and origin are unknown disappeared during transformation. The mean cell volume for metacyclic forms was 15-16 microns3. During transformation the values first dropped and then increased to about 20 microns3 after 24 h.