CyanoAsterisMETAB · Exploration of the biosynthetic potential of the secondary metabolome of the newly identified fungal endophyte Cyanodermella asteris

Exploration of the biosynthetic potential of the secondary metabolome of the newly identified fungal endophyte Cyanodermella asteris

Traditionally, identification of bioactive compounds from different natural sources (e.g., plants, fungi and bacteria) has always been an important avenue for pharmaceutical discovery efforts. Due to these endeavors, various classes of pharmaceuticals, such as antibiotics (e.g., -lactams, tetracycline, macrolides), antiparasitics (e.g., avermectin), antiprotozoals (e.g., artemisinin), immunosuppressive drugs (e.g., rapamycins) and antineoplastic agents (e.g., paclitaxel, doxorubicin) have been discovered and proved to be highly relevant for clinical application. In this regard, The Fungal Kingdom has played a key role. Especially after the groundbreaking discovery of penicillin, the world experienced an enormous interest to explore various fungal sources aiming to identify new antimicrobial compounds and other medically useful agents, such as the lipid-lowering agents (e.g., lovastatin) and immunosuppressive drugs (e.g., cyclosporine). Nowadays, an increasing interest for fungal natural products (NPs) has been encountered. This is mainly triggered by the availability of whole-genome information for different fungal species and by the tremendous progress in bioinformatics, genetic manipulation techniques and analytical technologies. Information gained from whole-genome sequences of different fungal species through powerful bioinformatic tools made us understand that the amount of NPs so far isolated from the fungal world is just a drop in the ocean compared to the great potential of NPs waiting to be explored. Hence, all these multidisciplinary advancements coupled with the urgent need for new antibiotics to treat life-threatening infections from resistant microorganisms, have once again made fungal-based NPs an attractive source for drug leads. Within the fungal world, endophytic fungi comprise an important source of species with multiple implications. An endophyte is a microorganism (fungi or bacteria) that lives within the plant tissues without causing apparent harmful health effects for the plant itself. Interestingly, in several cases it was demonstrated that fungal endophytes are responsible for the production of bioactive compounds which were originally reported as products of the respective fungal host plants. To illustrate this concept, currently it was demonstrated the direct implication of fungal endophytes in the biosynthesis of the anti-tumor/immunosuppressive astins which were originally reported to be produced by the traditional Chinese medicinal plant Aster tataricus L. The fungal endophyte involved in astins biosynthesis was isolated from flowering parts of A. tataricus L. and named Cyanodermella asteris. Since the majority of biosynthetic gene clusters (BGCs) from C. asteris seem to be silent or expressed in very low yields under laboratory conditions, we hypothesize that C. asteris possesses a substantial hidden potential for novel and possibly bioactive natural products (NPs). In this regard, we explored several in silico-predicted BGCs, which have been examined within the framework of this project. Hence, the main aim of this project was to elucidate the chemical products of the selected BGCs by cloning, heterologous expression as well as via metabolome mining and secondary metabolomics of the wild-type species C. asteris. The main objectives of the intended project are: - Objective 1: Cloning and vector construction of the selected BGCs. The aim of this objective was that bioinformatically selected BGCs to be cloned in suitable vectors for fungal transformation. - Objective 2: Heterologous expression of selected BGCs in suitable fungal hosts. The purpose of this objective was that constructed vectors harboring BGCs of interest to be transformed via protoplastation into heterologous fungal hosts such as Aspergillus oryzae. - Objective 3: HRMS-based metabolomics and dereplication of comparative metabolomes. The purpose of this objective was annotation of metabolites making the difference between transformed and native (isogenic) fungal hosts via global untargeted metabolomics comparison. In case of biomarker annotation, dereplication strategies using in-house and comprehensive external databases (e.g. Antibase) as well as online tandem MS-based infrastructures (e.g. GNPS) will be used. Metabolome mining of the wild-type was also explored in detail. - Objective 4: Isolation and structure elucidation of novel natural products from selected BGCs. The aim of the last objective was to perform classical compound purification and subsequent structural elucidation in the case of unsuccessful dereplication due to structural novelty.

Data: CORDIS, © European Union