Electron Microscope Study of the Proliferative Form of Besnoitia jellisoni

Abstract

Electron microscope studies of the proliferative form of Besnoitia jellisoni confirm its close relationship to Toxoplasma gondii. Its pellicle consists of an outer and an inner membrane under which 22 longitudinal fibrils are found. A micropyle is formed by an invagination of the outer membrane. At the anterior end a polar ring surrounds the conoid. Club-like "toxonemes" extend posteriorly from within the conoid. A large vesicle with a tube connecting its lumen to the exterior through the conoid may represent a feeding mechanism. One or 2 mitochondria, rough endoplasmic reticulum, and free ribosomes are distributed throughout the cytoplasm. The Golgi zone is anterior to the nucleus. A large vacuole of unknown function is found near the Golgi zone. Endodyogeny, a division by internal budding, occurs producing 2 daughter cells within a parent cell. Stages possibly representing binary fission were also observed.