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Metabolites from the Fungal Endophyte Aspergillus austroafricanus in Axenic Culture and in Fungal–Bacterial Mixed Cultures
journal contribution
posted on 2016-04-12, 19:16 authored by Weaam Ebrahim, Mona El-Neketi, Laura-Isabell Lewald, Raha S. Orfali, Wenhan Lin, Nidja Rehberg, Rainer Kalscheuer, Georgios Daletos, Peter ProkschThe endophytic fungus Aspergillus
austroafricanus isolated from leaves of the aquatic plant Eichhornia crassipes was fermented axenically on solid rice
medium as well as in mixed
cultures with Bacillus subtilis or with Streptomyces
lividans. Chromatographic analysis of EtOAc extract of axenic
cultures afforded two new metabolites, namely, the xanthone dimer
austradixanthone (1) and the sesquiterpene (+)-austrosene
(2), along with five known compounds (3–7). Austradixanthone (1) represents the first
highly oxygenated heterodimeric xanthone derivative. When A. austroafricanus was grown in mixed cultures with B. subtilis or with S. lividans, several
diphenyl ethers (8–11) including
the new austramide (8) were induced up to 29-fold. The
structures of new compounds were unambiguously elucidated using 1D-
and 2D-NMR spectroscopy, HRESIMS, and chemical derivatization. Compound 7 exhibited weak cytotoxicity against the murine lymphoma
L5178Y cell line (EC50 is 12.6 μM). In addition,
compounds 9 and 10, which were enhanced
in mixed fungal/bacterial cultures, proved to be active against Staphylococcus aureus (ATCC 700699) with minimal inhibitory
concentrations (MICs) of 25 μM each (6.6 μg/mL), whereas
compound 11 revealed moderate antibacterial activity
against B. subtilis 168 trpC2 with an MIC value of
34.8 μM (8 μg/mL).
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chemical derivatization12.6 μ MFungal Endophyte Aspergillus austroafricanusBacillus subtilisdiphenyl ethersoxygenated heterodimeric xanthoneStreptomyces lividans25 μ Mxanthone dimer austradixanthoneATCCMIC valueEC 50compounds 9Chromatographic analysis1 Dplant Eichhornia crassipesCompound 7Axenic CultureStaphylococcus aureusaxenic culturescompound 11endophytic fungus Aspergillus austroafricanussubtilis 168 trpC 2rice mediumHRESIMSmurine lymphoma L 5178Y cell line
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