Candida albicans formed germ tubes when exposed to air containing 5 to 15% carbon dioxide (CO2). The CO2-mediated germ tube formation occurred optimally at 37 degrees C in a pH range of 5.5 to 6.5. No germ tubes were produced at 25 degrees C, even when the optimal concentration of CO2 (10%) was present in the environment. The requirement of CO2 for germ tube formation could be partially substituted by sodium bicarbonate but not by N2. Carbon dioxide was required to be present throughout the entire course of germ tube emergence suggesting that its role is not limited to an initial triggering of morphogenic change. We suggest that carbon dioxide may be a common effector responsible for the germ tube promoting activity of certain chemical inducers for C. albicans.

The formation of arthroconidia, especially the ontogeny of the arthroconidial wall in the dermatophyte Trichophyton mentagrophytes, was investigated by light and electron microscopy. Time-lapse photomicroscopy revealed that the new septa were inserted regularly along the length of the hypha. Each new septum divided a preexisting hyphal segment into approximately equal halves. The initial sign of arthroconidium formation detected by electron microscopy was the deposition of a conidium-specific wall layer on the inner surface of the preexisting hyphal wall. The invaginating septal material was continuous with the newly deposited inner wall layer of the sporulating hyphae. When septation was completed, the septum and septal furrow were continuous across the wall to the inner edge of the outer wall layer. After septation, the inner wall continued to thicken until it attained the thickness of a mature arthroconidial wall (0.3 – 0.5 μm). Simultaneously, immature arthroconidia continued to swell and eventually assumed a barrel shape. When disarticulated, arthroconidia were surrounded by the newly formed conidial wall at the poles, and the sides of the conidia were additionally bounded by the residual hyphal wall. As the arthroconidia matured, the remnants of the hyphal wall tended to be detached from the spore surface. From these observations we conclude that T. mentagrophytes formed arthroconidia by the enteroarthric mode rather than the holoarthric process as previously described.

No abstract