Fungal growth in culture media simulating an extreme environment.

BACKGROUND There is an increasing interest in the study of microorganisms that inhabit extreme environments for reasons that vary from gaining insight into the origin of life to the searching of new biotechnological applications. AIMS In this work, we studied the tolerance of fungi isolated from the Aguas Agrias Stream (AAS; Tharsis, Huelva, Spain), an acidic metal-rich environment, to a culture medium prepared with water from this extreme ecosystem (AASW medium). The ability of some culture collection strains of moulds and yeasts to grow on AASW medium was also assessed. METHODS For moulds, a tolerance index was calculated by dividing the growth diameter of colonies on AASW medium by the diameter in the control medium, and their germinative potential was recorded. For yeasts and yeast-like fungi, the minimum inhibitory concentration of AASW was determined. RESULTS In general, the fungi isolated from the AAS showed differences in their ability to germinate and grow on AASW medium. Collection strains of the genus Aspergillus could grow on AASW medium, but showed some differences in tolerance when compared to environmental isolates. CONCLUSIONS Extremotolerant fungi can manifest differences in their tolerance to culture media that simulate the conditions of their natural habitat. The results of this work suggest that the ability of fungi to grow in acidic, metal-rich environments might be more widespread than previously thought, and highlight the importance of determining the factors that are responsible for tolerance to these extreme environments.