Electron Microscopic Observation of the Sporangial Structure of Strains of Actinoplanaceae

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Abstract
Eight strains of Streptosporangium spp. and one strain each of Spirillospora albida and an Ampullariella-like Actinoplanes sp. were observed by electron microscopy. The sporangiospores of all these organisms had a smooth surface. All formed their sporangia by the ingrowth of a hypha inside a bag formed by the extension of the outer sheath of the sporangiophore. The sporogenic hypha was not branched in strains of Streptosporangium but was branched in S. albida and the Actinoplanes sp. Spore formation was by septation of the intrasporangial hyphae. When it occurred, septation took place by the same annular ingrowth of the cell wall common in gram-positive bacteria. The septum at the apex of the sporangiophore was formed before the others. Septation was seen to occur between two fully formed septa, indicating almost simultaneous formation of large segments dividing again, almost simultaneously, into smaller spore-sized segments.