Pneumocystis carinii Delanoë, its Ultrastructure and Ultrastructural Affinities*

Abstract

SYNOPSIS The fine structure of Pneumocystis carinii Delanoë 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.

Propagation of Pneumocystis carinii in Vitro

“…The ultrastructural features of P. carinii in culture were identical with those described from transmission electron microscopy studies of the organism in naturally infected rat and human lungs (2,5,20,21,37). The organisms were distinct from other structures in the CEL cell cultures when comparison was made between infected and uninfected cell cultures.…”

The Pneumocystis life cycle

“…Although many authors (for instance, Jirovec 1964, Kim et al 1972 suggested hypotheses regarding the Pneumocystis life cycle, the best ones were based on ultrastructural observations (Vavra & Kucera 1970, Campbell 1972, Vossen et al 1978, Matsumoto & Yoshida 1984, Yoshida 1989, Dei-Cas 2000. Thus, a major event in the history of Pneumocystis life cycle research was undoubtedly the finding of synaptonemal complexes in the nucleus of early sporocytes, indicating the occurrence of a meiotic division, i.e., of a sexual cycle (Matsumoto & Yoshida 1984).…”

“…The fungal nature of Pneumocystis was suggested by Vavra and Kucera (1970) on the basis of ultrastructural studies. It was further strengthened by Ruffolo (1994) when he proposed to rename the Pneumocystis stages according to fungal terminology.…”

Basic biology of Pneumocystis carinii: a mini review

“…The cytoplasm of the trophozoite is poor in organelles (Vavra & Kucera 1970). Free ribosomes predominate.…”