Leaf-cutting ants cultivate the fungus Leucoagaricus gongylophorus, which serves as a major food source. This symbiosis is threatened by microbial pathogens that can severely infect L. gongylophorus. Microbial symbionts of leaf-cutting ants, mainly Pseudonocardia and Streptomyces, support the ants in defending their fungus gardens against infections by supplying antimicrobial and antifungal compounds. The ecological role of microorganisms in the nests of leaf-cutting ants can only be addressed in detail if their secondary metabolites are known. Here, we use an approach for the rapid identification of established bioactive compounds from microorganisms in ecological contexts by combining phylogenetic data, database searches, and liquid chromatography electrospray ionisation high resolution mass spectrometry (LC-ESI-HR-MS) screening. Antimycins A 1 -A 4 , valinomycins, and actinomycins were identified in this manner from Streptomyces symbionts of leaf-cutting ants. Matrix-assisted laser desorption ionization (MALDI) imaging revealed the distribution of valinomycin directly on the integument of Acromyrmex echinatior workers. Valinomycins and actinomycins were also directly identified in samples from the waste of A. echinatior and A. niger leaf-cutting ants, suggesting that the compounds exert their antimicrobial and antifungal potential in the nests of leaf-cutting ants. Strong synergistic effects of the secondary metabolites produced by ant-associated Streptomyces were observed in the agar diffusion assay against Escovopsis weberi. Actinomycins strongly inhibit soil bacteria as well as other Streptomyces and Pseudonocardia symbionts. The antifungal antimycins are not only active against pathogenic fungi but also the garden fungus L. gongylophorus itself. In conclusion, secondary metabolites of microbial symbionts of leaf-cutting ants contribute to shaping the microbial communities within the nests of leaf-cutting ants.

The new 1,2: The feeding of fluorine‐labelled precursors together with mutagenesis experiments revealed that the rare 3‐amino‐salicylate moiety of antimycins is produced by a particular multicomponent oxidation complex.

The volatiles released by several streptomycetes were collected by using a closed-loop stripping apparatus (CLSA) and analysed by GC-MS. The obtained headspace extracts of various species contained blastmycinone, a known degradation product of the fungicidal antibiotic, antimycin A(3b), and several unknown derivatives. The suggested structures of these compounds, based on their mass spectra and GC retention indices, were confirmed by comparison to synthetic reference samples. Additional compounds found in the headspace extracts were butenolides formed from the blastmycinones by elimination of the carboxylic acid moiety. Analysis of a gene knockout mutant in the antimycin biosynthetic gene cluster demonstrated that all blastmycinones and butenolides are formed via the antimycin biosynthetic pathway. The structural variation of the blastmycinones identified here is much larger than within the known antimycins, thus suggesting that several antimycin derivatives remain to be discovered.