Quantitative Ultrastructural Differences between Strains of the Trypanosoma brucei Subgroup During Transformation in Blood*

SYNOPSIS. Differences in the relative and absolute cell organization between strains of the Trypanosoma brucei subgroup were studied during the transformation from slender to stumpy bloodforms. Two pleomorphic and 1 monomorphic T. b. brucei, and 1 pleomorphic T. b. rhodesiense strains were investigated. Volume densities, surface densities and surface to volume ratios showed barely significant differences between the 2 pleomorphic T. b. brucei strains; absolute parameters, however, differ markedly between all the strains investigated. Only the relative parameters of the mitochondrion show notable differences between T. b. brucei and T. b. rhodesiense examined here. During the transformation from slender to stumpy forms the enlargement of the mitochondrial volume in T. b. brucei is achieved by an increase in width of the mitochondrial tube and in T. b. rhodesiense by the formation of a more elaborate network. The ratio of the inner mitochondrial membrane surface area to the mitochondrial matrix volume showed no significant change in all 3 pleomorphic strains examined. Because of their morphometric similarity to slender forms of pleomorphic T. b. brucei strains, it can be assumed that the monomorphic trypanosomes correspond morphologically to slender trypanosomes. Neither pleomorphism nor strain specificity have a significant influence on the relative amount of “vesicles” and lipid inclusions.