Chemical Ecology/Biological Chemistry, University of Konstanz, Universitätsstraße 10, 78457, Konstanz, Germany.
Plant Ecology and Systematics, Technical University Kaiserslautern, Erwin-Schrödingerstraße 13, 67653, Kaiserslautern, Germany.
Chemistry. 2018 Mar 20;24(17):4445-4452. doi: 10.1002/chem.201706071. Epub 2018 Feb 22.
The specialized, fungal pathogen Escovopsis weberi threatens the mutualistic symbiosis between leaf-cutting ants and their garden fungus (Leucoagaricus gongylophorus). Because E. weberi can overwhelm L. gongylophorus without direct contact, it was suspected to secrete toxins. Using NMR and mass spectrometry, we identified several secondary metabolites produced by E. weberi. E. weberi produces five shearinine-type indole triterpenoids including two novel derivatives, shearinine L and shearinine M, as well as the polyketides, emodin and cycloarthropsone. Cycloarthropsone and emodin strongly inhibited the growth of the garden fungus L. gongylophorous at 0.8 and 0.7 μmol, respectively. Emodin was also active against Streptomyces microbial symbionts (0.3 μmol) of leaf-cutting ants. Shearinine L instead did not affect the growth of L. gongylophorus in agar diffusion assays. However, in dual choice behavioral assays Acromyrmex octospinosus ants clearly avoided substrate treated with shearinine L for the garden fungus after a 2 d learning period, indicating that the ants quickly learn to avoid shearinine L.
专门的真菌病原体 Escovopsis weberi 威胁着切叶蚁与其共生真菌（Leucoagaricus gongylophorus）之间的互利共生关系。由于 E. weberi 可以在没有直接接触的情况下压倒 L. gongylophorus，因此怀疑它会分泌毒素。使用 NMR 和质谱，我们鉴定了 E. weberi 产生的几种次级代谢产物。E. weberi 产生了五种 shearinine 型吲哚三萜，包括两种新型衍生物 shearinine L 和 shearinine M，以及 polyketides emodin 和 cycloarthropsone。Cycloarthropsone 和 emodin 在 0.8 和 0.7 μmol 时强烈抑制了共生真菌 L. gongylophorous 的生长。Emodin 对切叶蚁的微生物共生体 Streptomyces 也具有活性（0.3 μmol）。Shearinine L 则在琼脂扩散试验中对 L. gongylophorus 的生长没有影响。然而，在双选择行为试验中，A. octospinosus 蚂蚁在 2 天的学习期后明显避免了含有 shearinine L 的基质处理的共生真菌，表明蚂蚁很快学会了避免 shearinine L。
