Definition for Dimorphic
From Biology Forums Dictionary
Dimorphic means two forms; pleiomorphic means more than one form. The terms are applied to fungi because they can have different forms, of hyphae or spores. At the most obvious, fungi commonly have sexual and asexual stages in their life cycles. What is less commonly understood, is that some fungi may have many morphologically different types of asexual spore. LINK Further, the thallus of some fungi may reversibly switch from spheres (yeast cells), to elongated conjoined buds (pseudohyphae), to filamentous (hyphae) under specific environmental conditions (temperature, energy, organic nitrogen, pH, oxygen, osmotic potential, minerals such as Ca etc). These forms are independent of one another and have quite specific developmental characteristics.
Many fungi produce two different spore types during asexual proliferation. Unfortunately, these states can cause confusion when the spore resembles those of other fungi. Similarity of form does not necessarily indicate relatedness, and care must be taken when naming fungi using asexual structures.
Yeast-like cells and hyphae of the dimorphic fungus Aureobasidium pullulans.
The nature of each form may also be under genetic control. Many fungi modify their growth according to the environmental conditions under which they grow. For instance, soil fungi have a sparse filamentous growth in culture when organic carbon is poorly available. When organic carbon is plentiful, the hyphae branch frequently, and the mycelium is dense. The net effect for the fungus is that in conditions of plentiful energy, the fungus is able to absorb large quantities, but when food is lacking, little energy is spent on exploring the location. In addition, different parts of a single mycelium may exhibit different forms: dense colonisaion of attractive and sparce colonisation (including presence of strands) of unattractive habitats. The main consequence of the variation in growth patterns is that fungi in soil thoroughly explore and efficiently exploit the highly variable and dynamic oligotrophic environment.
