Pneumocystis carinii Delanoë, its ultrastructure and ultrastructural affinities.

TLDR: It is concluded from the ultrastructural evidence that Pneumocystis may indeed be a yeast or have a yeast-like stage in its life cycle, but it is not completely similar to any fungus whose ultrastructure has been described so far.

Abstract: SYNOPSIS The fine structure of Pneumocystis carinii Delanoe is described in detail and is compared to the fine structure of protozoa and fungi. Pneumocystis does not have ultrastructural affinities to Protozoa but rather to fungi. Specifically, the process of intracystic body formation in the cyst is similar to the formation of ascospores inside a yeast ascus. The significance of the structural similarity between Pneumocystis and fungi is discussed. It is concluded from the ultrastructural evidence that Pneumocystis may indeed be a yeast or have a yeast-like stage in its life cycle. However, Pneumocystis is not completely similar to any fungus whose ultrastructure has been described so far. Perhaps its particular structure may be an adaptation to the parasitic way of life in mammalian lungs. It should be cultivated in order to be sure of its exact taxonomic position.