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Endophytic Streptomyces in the traditional medicinal plant Arnica montana L.: secondary metabolites and biological activity

Wardecki, Tina, Brötz, Elke, De Ford, Christian, von Loewenich, Friederike D., Rebets, Yuriy, Tokovenko, Bogdan, Luzhetskyy, Andriy, Merfort, Irmgard
Antonie van Leeuwenhoek 2015 v.108 no.2 pp. 391-402
Arnica montana, Candida parapsilosis, Fusarium verticillioides, Gram-positive bacteria, Staphylococcus aureus, Streptomyces, antibiotics, antifungal properties, cycloheximide, cytotoxicity, diketopiperazines, endophytes, medicinal plants, multigene family, mycorrhizal fungi, nutrients, pathogens, plant growth, secondary metabolites, sequence analysis, sesquiterpenoid lactones, soil, symbiosis
Arnica montana L. is a medical plant of the Asteraceae family and grows preferably on nutrient poor soils in mountainous environments. Such surroundings are known to make plants dependent on symbiosis with other organisms. Up to now only arbuscular mycorrhizal fungi were found to act as endophytic symbiosis partners for A. montana. Here we identified five Streptomyces strains, microorganisms also known to occur as endophytes in plants and to produce a huge variety of active secondary metabolites, as inhabitants of A. montana. The secondary metabolite spectrum of these strains does not contain sesquiterpene lactones, but consists of the glutarimide antibiotics cycloheximide and actiphenol as well as the diketopiperazines cyclo-prolyl-valyl, cyclo-prolyl-isoleucyl, cyclo-prolyl-leucyl and cyclo-prolyl-phenylalanyl. Notably, genome analysis of one strain was performed and indicated a huge genome size with a high number of natural products gene clusters among which genes for cycloheximide production were detected. Only weak activity against the Gram-positive bacterium Staphylococcus aureus was revealed, but the extracts showed a marked cytotoxic activity as well as an antifungal activity against Candida parapsilosis and Fusarium verticillioides. Altogether, our results provide evidence that A. montana and its endophytic Streptomyces benefit from each other by completing their protection against competitors and pathogens and by exchanging plant growth promoting signals with nutrients.