Author contributions and conflict of interest Daniel Braga performed research, analyzed data (molecular biology, malachite green assay, mass spectrometry) and contributed to writing the manuscript, Daniel Last performed research and analyzed data (structure elucidation, Fno assay, biogas plant studies), Mahmudul Hasan performed research (CofC/D enzyme assays), Huijuan Guo performed research and analyzed data (structure elucidation), Daniel Leichnitz performed research (chemical synthesis), Zerrin Uzum performed research (microscopy), Ingrid Richter performed research (microscopy), Felix Schalk performed research (cofE constructs), Christine Beemelmanns designed research, acquired funding, analyzed data (structure elucidation, synthesis) and edited the manuscript, Christian Hertweck designed research, acquired funding and edited the manuscript, Gerald Lackner designed the study, acquired funding and wrote the original manuscript. The authors declare no conflict of interest.

Fungus-growing termites have optimized the decomposition of recalcitrant plant biomass to access valuable nutrients by engaging in a tripartite symbiosis with complementary contributions from a fungal mutualist and a codiversified gut microbiome. This complex symbiotic interplay makes them one of the most successful and important decomposers for carbon cycling in Old World ecosystems.

In this study, we analyzed if Actinomadura sp. RB99 produces siderophores that that could be responsible for the antimicrobial activity observed in co-cultivation studies. Dereplication of high-resolution tandem mass spectrometry (HRMS/MS) and global natural product social molecular networking platform (GNPS) analysis of fungus-bacterium cocultures resulted in the identification of five madurastatin derivatives (A1, A2, E1, F, and G1), of which were four new derivatives. Chemical structures were unambiguously confirmed by HR-ESI-MS, 1D and 2D NMR experiments, as well as MS/MS data and their absolute structures were elucidated based on Marfey's analysis, DP4 + probability calculation and total synthesis. Structure analysis revealed that madurastatin E1 (2) contained a rare 4-imidazolidinone cyclic moiety and madurastatin A1 (5) was characterized as a Ga 3 + -complex. The function of madurastatins as siderophores was evaluated using the fungal pathogen Cryptococcus neoformans as model organism. Based on homology models, we identified the putative NRPS-based gene cluster region of the siderophores in Actinomadura sp. RB99.

Dedicated to Prof. Rolf Huisgen. Herein, we report the targeted isolation and characterization of four linear nonribosomally synthesized tetrapeptides (pseudoxylaramide AD) and two cyclic nonribosomal peptide synthetase-polyketide synthase-derived natural products (xylacremolide A and B) from the termite-associated stowaway fungus Pseudoxylaria sp. X187. The fungal strain was prioritized for further metabolic analysis based on its taxonomical position and morphological and bioassay data. Metabolic data were dereplicated based on high-resolution tandem mass spectrometry data and global molecular networking analysis. The structure of all six new natural products was elucidated based on a combination of 1D and 2D NMR analysis, Marfey's analysis and X-ray crystallography.

23 Phone: +49 3631 532 1104 24 25 Author contributions and conflict of interest 26 Daniel Braga performed research, analyzed data (molecular biology, malachite green assay, mass spectrometry) 27 and contributed to writing the manuscript, Daniel Last performed research and analyzed data (structure 28 elucidation, Fno assay, biogas plant studies), Mahmudul Hasan performed research (CofC/D enzyme assays), 29 Huijuan Guo performed research and analyzed data (structure elucidation), Daniel Leichnitz performed research 30 (chemical synthesis), Zerrin Uzum performed research (microscopy), Ingrid Richter performed research 31 (microscopy), Felix Schalk performed research (cofE constructs), Christine Beemelmanns designed research, 32 acquired funding, analyzed data (structure elucidation, synthesis) and edited the manuscript, Christian Hertweck 33 designed research, acquired funding and edited the manuscript, Gerald Lackner designed the study, acquired 34 funding and wrote the original manuscript. The authors declare no conflict of interest. 35 Abstract 1