Structures of the motile cells of Coelomomyces psorophorae and function of the zygote in encystment on a host

Abstract

Coelomomyces psorophorae is an aquatic fungus in the order Blastocladiales. Its motile zoospores and zygote transmit this pathogen to its copepod and mosquito larval hosts, respectively. In copepods, the fungal mycelium gives rise to isogametes, which fuse to form zygotes.The fine structure of the motile cells: zoospore, isogamete, and zygote, is reported. Morphology is compared with spore structure of other fungi in the order, and a model is proposed for a blastocladialian parasitic spore type. Features of this parasitic spore include close mitochondrial–nuclear contact, asymmetrical nucleus, internal axoneme, vestigial kinetosome lacking, and presence of adhesion vesicles.Encystment of zygotes on the cuticle of larvae of the mosquito Culiseta inornata appears to involve secretion of the contents of adhesion vesicles. Subsequent events include cell wall formation and dedifferentiation of specialized zygote structures.