The adhesive droplet of capilliconidia of Basidiobolus ranarum exhibits unique ultrastructural features

Abstract

The capilliconidia of Basidiobolus ranarum produce an apical droplet of extracellular material that aids in dispersal by arthropods, such as mites and termites. Electron microscopic examination of the adhesive material comprising the haptor of capilliconidia has shown it to consist of an electron-dense band directly around the capilliconidial beak from which sinuous fibrous filaments extend radially. These filaments are partially digestible with proteinase-K and measure 18–20 nm wide by 3–4 μm long. Interspersed among the filaments are double membrane-bound ovoid organelles that are 0.2-0.3 μm × 0.3-0.4 μm and which contain electron-dense granular contents. Overlying the layer of sinuous filaments is a looser layer of coarsely fibrogranular material that, in turn, is covered with an outermost layer of densely granular material. What are interpreted to be earlier stages of adhesive formation exhibit an almost homogeneous appearance of the haptor material. No clearly defined wall or membrane delimits the droplet surface. A comparison is made between this adhesive material and that reported for other fungi.

Key Words:

• Basidiobolus
• capilliconidia
• adhesives