The hyphal tip structure of Basidiobolus sp.: a zygomycete fungus of uncertain phylogeny.

To date, among the zygomycete fungi that have been examined, a Spitzenkörper has not been reported. In this paper, the cytoplasmic order of hyphal tip cells of Basidiobolus sp., a zygomycete genus of uncertain phylogeny, has been examined using light microscopy and transmission electron microscopy methods. With phase-contrast light optics, a phase-dark body was observed at the tips of growing hyphae of Basidiobolus sp. The hyphal apex also showed high affinity for FM4-64 labelling resulting in an intense fluorescence signal. The phase-dark inclusion exhibited independent motility within the hyphal apex and its presence and position were correlated to the rate and direction of hyphal growth. The hyphal apex of Basidiobolus sp. did not contain γ-tubulin. Ultrastructural observations revealed a dense cluster of vesicles at the hyphal apex. These results suggest that the growing hypha of Basidiobolus sp. contains a Spitzenkörper, a character generally attributed to members of the ascomycete and basidiomycete fungi and not to zygomycete fungi.