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The stress biology of extremophile fungi and the nature of fungal interactions with algae

February 27, 2015


Dr. Steven Harris
University of Nebraska

Friday, February 27 @ 3:30 p.m.
Biology Lecture Theatre (Rm. 106 Biology)
W.P. Thompson (Biology) Building

Extremophiles are broadly recognized as organisms that can live in extreme conditions of temperature, acidity, alkalinity, or salinity. Besides expanding our views on the diversity of life on Earth and perhaps beyond, the study of extremophiles has also provided significant insight
into how organisms adapt to stress. Extremophile fungi that primarily colonize exposed rock surfaces, known as “rock inhabiting fungi’ (RIFs), were originally discovered in Antarctica, but have since been found throughout temperate habitats. RIFs possess numerous morphological and physiological adaptations that allow them to thrive in harsh environments that would normally preclude survival. We propose that the “model” black yeast Exophiala dermatitidis can be used to investigate the molecular basis of these adaptations. The accumulation of pigments such as melanin and carotenoids likely play a key role in the stress tolerance of E. dermatitidis. In their functional characterization of the GTPases Cdc42 and Rac1, Guo and Szaniszlo (unpub.) noted that the absence of Cdc42 resulted in the apparent loss of carotenoids. We have confirmed this and shown that cdc42 mutants fail to induce the carotenoid biosynthetic gene cluster. We are currently using transcriptome sequencing to better define the role of Cdc42 in pigment synthesis and broader stress responses. We also discovered that E. dermatitidis can engage in transient mutualisms with photosynthetic algae to support growth and development. This was accomplished by co-culturing E. dermatitidis with the alga Chlorella sorokiniana in the presence of light on a minimal medium that otherwise lacked carbon. Preliminary results show that co- cultivation markedly enhances growth and favours stable associations between fungal and algal cells. Our results also suggest that algal phytohormones trigger the accumulation of lipid bodies in E. dermatitidis, and imply that transient mutualisms play a significant role in enabling the survival of extremophile fungi in harsh environments.

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