Ultrastructure of natural and induced myxospores of Archangium gephyra

Abstract

The ultrastructure of natural myxospores and glycerol-induced myxospores has been studied in four Archangium gephyra strains (AG3, AG5, AG9, and AG10). The induced myxospores show an oval shape, characteristic of the genus Archangium, and an electron-dense coat surrounds the cell wall. The cytoplasm contains abundant electron-lucent inclusions. Sometimes, a membranous structure appears between the coat and the outer membrane. The fruiting-body myxospores show an oval shape similar to that observed in induced myxospores, but with a slightly thicker outer coat. In many of the natural myxospores, some membranous, lamellar or vesicular structures appear. They are located between the coat and the outer membrane, resembling those that appeared in induced myxospores. These have not been previously mentioned in papers on fruiting-body myxospores. These structures occasionally seem to be fused, giving rise to membranous sacs filled with an amorphous material of medium electron density. We propose that these vesicles are formed from the waved outer membrane and from the fruiting-body matrix. Large, dense, fusiform inclusions with an internal crystalline array are frequently found in the cytoplasm of natural myxospores, and cells during differentiation, in strains AG3, AG9, and AG10. Key words: Archangium gephyra, electron microscopy, myxospores, ultrastructure.