MICROSPORIDIAN SPORE WALL - ULTRASTRUCTURAL FINDINGS ON ENCEPHALITOZOON HELLEM EXOSPORE

A study of the spore wall of Encephalitozoon hellem was performed on t hin sections, freeze-fracture, and deep-etched samples to obtain infor mation on spore wall organization and composition. Our observations de monstrate that the spore wall is formed by an inner 30-35 nm electron- lucent endospore and an outer 25-30 nm electron-dense exospore. The ex ospore is a complex of three layers: an outer spiny layer, an electron -lucent intermediate lamina and an inner fibrous layer. Freeze-fractur e and deep-etching techniques reveal that the intermediate lamina and the inner fibrous layer result from the different spatial disposition of the same 4-nm thick fibrils. In thin sections the endospore reveals a scattered electron-dense material that appears in the form of trabe cular structures when analyzed in deep-etched samples. The presence of chitin in the exospore is discussed.