This study describes the ultrastructure of septa (cross-walls) in Dimargaris cristalligena, a mycoparasite fungus that parasitizes members of the Mucorales order. Using electron microscopy with potassium permanganate and aldehyde-osmium fixation methods, researchers examined the fine structure of septa in vegetative hyphae, sporangiophores, and infection structures. The vegetative hyphal septum features a central pore with a flared margin containing an electron-dense plug, flanked by globose bodies surrounded by ribosome-free cytoplasm on each side. Cytoplasmic continuity is maintained through the pore via the plasmalemma. In sporangiophores and sporulating structures, the septal plug exhibits different morphology, with an upper globose protuberance and lower obconic lobe. The related species Tieghemiomyces californicus displays similar septal ultrastructure. The complex septum is characteristic of the Dimargaritaceae family and may have taxonomic significance. The authors suggest the septal plugs could regulate cytoplasmic flow or prevent excessive cytoplasm loss following cell breakage, though experimental evidence is lacking. These findings support distinguishing the Dimargaritaceae from other related fungal orders based on septal morphology.

Key findings

• Dimargaritis cristalligena septa contain a central pore with an electron-dense plug flanked by globose bodies, a structure unique to the Dimargaritaceae family
• Vegetative hyphal septa differ morphologically from sporangiophore septa, which possess asymmetric plug lobes (globose upper, obconic lower)
• The septal plug appears soluble in dilute alkali and can regulate cytoplasmic flow between hyphal compartments
• Similar septal ultrastructure in Tieghemiomyces californicus confirms this morphology as a characteristic family trait with taxonomic importance