[Fine structure of the vegetative and spore-forming hyphae of Micropolyspora fascifera]

Changes in the fine structure of the hyphae were studied in the course of spore formation by Micropolyspora fascifera. Sporulating hyphae differ from vegetative hyphae by a less dense cytoplasm, a large zone of the nucleoid with distinctly fibrillar structure, and a thin layerless cell wall. Spore formation is accompanied with autolysis of the vegetative hyphae, which consists in vacuolization of the hyphae and appearance of a large number of tubular membrane structures within them. Spores are formed, like in Actinomyces spp., by simultaneous division of the hyphae with septa; the structure of sporulating septa is similar to that of the fragmenting mycelium in Nocardia; the structure of mature spores is similar to that in some Actinomyces spp. Therefore, M. fascifera differs from other Micropolyspora spp. not only by the chemical composition of the cells (the presence of nocardiomicolic acids) but also by their structure. Taxonomic position of the species is discussed.