ELECTRON MICROSCOPIC STUDY OF THE FORMATION OF SPINY CONIDIA IN SPECIES OF STREPTOMYCES

Abstract

The mode of formation of conidia by a strain of Streptomyces viridochromogenes was followed by the observation of ultrathin sections of aerial hyphae at various stages of sporulation. Before sporulation the aerial hyphae contain a long central strand of nuclear material. The laminated hyphal wall is covered with a fibrous non-spiny layer. At equal intervals, and apparently simultaneously, the hyphal wall becomes involuted while the outer fibrous sheath becomes spiny. The nuclear material constricts, adjacent to the points of involution of the wall. As the involution of the cell wall continues, only a thin isthmus of cytoplasm connects two adjacent future spores. The nuclear material breaks into spheroid structures. The spiny fibrous layer breaks into spore size segments that envelop each spore. An amorphous electron dense material accumulates between adjacent spores during maturation and eventually participates in the formation of interspore pads. Spores in a chain are held together only by the fusion between adjacent interspore pads. As the spores in a chain become fully mature, an area of weakness can be seen between spore pads that are still held together. Although studied in less detail, the mechanism of spore formation is believed to be similar in a strain of S. violaceus.