Ultrastructural changes in the cell surface of Coelomomyces punctatus infecting mosquito larvae

As the fungus Coelomomyces punctatus develops in the coelomic cavity of the mosquito Anopheles quadrimaculatus, the conformation of the plasma membrane and extracellular coat of the fungus changes markedly. The vegetative stage was surrounded by a granular and fibrillar extracellular coat which reacted positively in the silver methenamine procedure for the localization of polysaccharides. Numerous simple, branched or contorted cytoplasmic protuberances covered the irregularly shaped hyphal bodies. The surface of the hyphal body adjacent to the fat body of the mosquito had occasional involutions of the plasma membrane sheathed by cisternae of endoplasmic reticulum. In contrast with these hyphal bodies, cytoplasmic protuberances were spaced at wide intervals along filamentous hyphae. Aborting thalli were contorted and deeply lobed. The plasma membrane was smooth, and cytoplasmic protuberances were absent on other hyphae and hyphal bodies, particularly at advanced stages of infection. Instead unattached vesicles, morphologically similar to the protuberances found on some thalli, were embedded in granular material clustered around the smooth plasma membrane of these thalli. Mosquito hemocytes appeared to engulf these vesicles and granular material. As the vegetative stage was transformed into the reproductive stage, a newly formed, compact extracellular layer surrounded the sporangial initial. Later, a darkly staining wall appeared around the resting sporangium. Cisternae of endoplasmic reticulum consistently subtended thin areas in this pitted wall.