The mechanism of cyclical development in trypanosomes of the Trypanosoma brucei sub-group: An hypothesis based on ultrastructural observations

Abstract

A comparison of the fine structure of blood-stream and culture (insect midgut) forms of trypanosomes of the T. brucei sub-group has shown that the two differ in the extent of the chondriome (mitochondria) which appears to arise from the kinetoplast. Blood-stream forms have a simple tubular anterior mitochondrion and no posterior mitochondrion. Culture forms have extensive and elaborate anterior mitochondria and a sinuous posterior mitochondrion extending from the kinetoplast to the posterior extremity of the flagellate. It is suggested that the morphological change evident in the trypanosome on transition from blood-stream to insect midgut is brought about by the outgrowth of this posterior mitochondrion which increases the distance between the kinetoplast and the posterior extremity of the flagellate. Proliferation of mitochondria by the kinetoplast is marked biochemically by a change in the pattern of respiration. This is probably an adaptation to life at a lower oxygen tension. It is thought possible that the physiological and morphological changes in cyclical development of trypanosomes of the T. brucei sub-group will prove intelligible in terms of the mitochondrial proliferation and regression demanded by the environment.