Fungal spore germination into yeast or mycelium: possible implications of dimorphism in evolution and human pathogenesis.

The ability of dimorphism in fungi is conventionally regarded as a reversible change between the two vegetative forms, yeast and mycelium, in response to environmental change. A zygomycetous isolate, Benjaminiella poitrasii, exhibited yeast-mycelium transition in response to the change in temperature (37-28 degrees C) and decrease in glucose concentration. For the first time the presence of dimorphic response during asexual and sexual spore germination is reported under the dimorphism-triggering conditions in B. poitrasii. The zygospores germinated into budding yeast when subjected to yeast-form supporting conditions. The mycelium-form favoring conditions gave rise to true mycelium. Similarly, the asexual spores displayed a dimorphic response during germination. Our observations suggest that dimorphism is an intrinsic ability present in the vegetative, asexual, and sexual forms of the fungus. As dimorphic fungi are intermediate to the unicellular yeast and the filamentous forms, understanding of the dimorphic character could be useful to trace the evolutionary relationships among taxonomically different fungi. Moreover, the implications of spore germination during the onset of pathogenesis and in drug development for human health care are discussed.