Adaptation strategies of Aspergillus species to environmental challenges

Abstract

Evolution shaped the adaptability of Aspergilli to diverse stress conditions, such as low temperature or adaptation to hostile environments. We applied different assays and multi-omics approaches to gain deeper understanding about these strategies. The determination of intracellular ATP levels during the freezing process revealed a high resistance of Aspergillus nidulans against cold- and cryostress, suggesting that A. nidulans is able to induce protective mechanisms to withstand environmental stresses. Large-scale proteomics, transcriptomics and metabolomics allowed us to gain insights into the low temperature response of this fungus at 10°C, which revealed an induction of cold protection mechanisms, sexual development and natural product biosynthesis. These findings indicated the existence of a light-independent mechanism to trigger sexual developmental regulated by cold. Further on, the production of so-far uncharacterised secondary metabolites with inhibitory effects against fungi and Gram-positive bacteria was induced, which may represent a valuable source for therapeutic compounds. Another stress is caused by human cells. The adaptation mechanisms of the regulation of extracellular protease secretion by deletion of the transcription factors XprG and PrtT in the human-pathogenic fungus Aspergillus fumigatus were characterised by an LC-MS/MS based proteomic approach. Despite an impaired degradation of substrate proteins, the double deletion strain XprG/PrtT did not show an attenuated virulence in a murine infection model of invasive aspergillosis. Furthermore, XprG and PrtT influenced additional processes, such as cell wall modifications and allergen production. Thus, the mutant strain XprG/PrtT may be useful for investigating the allergic response to fungal protein antigens. In summary, Aspergilli used in this study showed strong adaptability to the applied stress conditions and a valuable multi-omics data set for future studies was generated.