Induced production of zinniol analogues by co-cultivation of two endophytic fungi in the same ecological niche
Graphical abstract
Introduction
Endophytic fungi have been proven to be an important source of natural products with unique structures and significant biological activities (Aly et al., 2013; Gao et al., 2018). However, under the standard laboratory culture conditions, most of their biosynthetic gene clusters (BGCs) are silent, and many cryptic secondary metabolites have not been explored (Rutledge and Challis, 2015; Scherlach and Hertweck, 2009). To date, some strategies have been developed to activate silent BGCs to obtain novel natural products (Li and Lou, 2018). Among them, co-cultivation is well-known as an effective approach to induce the expression of BGCs through promoting interspecies interaction (Marmann et al., 2014; Chen et al., 2015). A plethora of traits, such as bioactive product formation (Wang et al., 2019), are typically involved in the interspecies interaction and improve the richness of microbial metabolites.
Recently, an endophytic fungus Pleosporales sp. F46, was isolated from the pedicel of the medicinal plant Mahonia fortunei by our research group (Li et al., 2019). Its rice culture fermentation afforded seven new heptaketides with antifungal or cytotoxic activities (Li et al., 2019). To maximize the chemical diversity of this fungal endophyte by promoting interspecies interaction, the co-cultivation of Pleosporales sp. F46 with the endophytic bacterium Bacillus wiedmannii Com1 was carried out, and a new antibacterial ergosterol was discovered (Wang et al., 2019). By further considering the interspecies interaction between endophytes in the same ecological niche, the endophytic fungus Acremonium pilosum F47, also isolated from the pedicel of M. fortunei, was selected for co-cultivation with Pleosporales sp. F46 in our current work. Herein, we report the isolation, characterization, and antibacterial evaluation of three new zinniol analogues, pleoniols A–C (1–3), via the co-cultivation of Pleosporales sp. F46 with A. pilosum F47.
Section snippets
Results and discussion
In the pre-screening period, the EtOAc extracts from the co-culture and axenic fermentations of endophytes in PDB media were analysed. HPLC-based metabolic profiling was performed to compare their metabolomes (Fig. 1). Several compounds were only detected when the endophytic fungus Pleosporales sp F46 was co-cultivated with A. pilosum F47 (Fig. 1), implying that several BGCs were activated. Further feeding experiments performed by adding sterilized fungal materials to culture media suggested
General experimental procedures
NMR spectra were recorded on a Bruker Advance spectrometer operating at 500 (1H) and 125 (13C) MHz. Mass spectra were obtained with an LTQ-Orbitrap spectrometer equipped with an ESI source. Optical rotation was measured on a Jasco P-1020 digital polarimeter (JASCO Corporation, Tokyo, Japan). IR spectra were obtained using a Cary 600 Series FTIR spectrometer (Agilent Technologies, Germany). Flash chromatography was performed on a Teledyne ISCO CombiFlash Rf 200 system equipped with a C18
Conclusions
Herein, we report the isolation and characterization of three new zinniol analogues, pleoniols A–C (1–3), and a known polyketide (4), from the co-cultivation of the endophytic fungi Pleosporales sp. F46 with A. pilosum F47. None of compounds 1–4 were detected when either one of the two fungi was cultured alone. The novel compounds 1–3 were evaluated for their antimicrobial and cytotoxic activities. Unfortunately, none of them were effective at the given concentrations against the tested
Declaration of Competing Interest
There are no competing conflicts to declare.
Acknowledgements
This work was supported by the National Natural Science Foundation of China [grant numbers 81903494 and 41706077]; and the Scientific Research Foundation of Qingdao University.
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