Cystochromones, Unusual Chromone-Containing Polyketides from the Myxobacterium <i>Cystobacter</i> sp. MCy9104

Seven new chromone-containing polyketides, termed cystochromones A–G, were isolated from the myxobacterial strain <i>Cystobacter</i> sp. MCy9104. Their structures were elucidated using comprehensive NMR spectroscopy and HR-MS/MS. Cystochromones bear a pentadecyl moiety unusually attached at C-5 of the chromone ring. Moreover, isotope-labeled substrate feeding experiments and NMR analysis suggested a hybrid iso-fatty acid and polyketide synthase biosynthetic pathway for these secondary metabolites

Microsclerodermins from Terrestrial Myxobacteria: An Intriguing Biosynthesis Likely Connected to a Sponge Symbiont

The microsclerodermins are unusual peptide natural products exhibiting potent antifungal activity reported from marine sponges of the genera Microscleroderma and Theonella. We here describe a variety of microbial producers of microsclerodermins and pedeins among myxobacteria along with the isolation of several new derivatives. A retrobiosynthetic approach led to the identification of microsclerodermin biosynthetic gene clusters in genomes of Sorangium and Jahnella species, allowing for the first time insights into the intriguing hybrid PKS/NRPS machinery required for microsclerodermin formation. This study reveals the biosynthesis of a “marine natural product” in a terrestrial myxobacterium where even the identical structure is available from both sources. Thus, the newly identified terrestrial producers provide access to additional chemical diversity; moreover, they are clearly more amenable to production optimization and genetic modification than the original source from the marine habitat. As sponge metagenome data strongly suggest the presence of associated myxobacteria, our findings underpin the recent notion that many previously described “sponge metabolites” might in fact originate from such microbial symbionts

Hyalachelins A–C, Unusual Siderophores Isolated from the Terrestrial Myxobacterium <i>Hyalangium minutum</i>

Three new siderophores, termed hyalachelins A–C (<b>1</b>–<b>3</b>), were isolated from the terrestrial myxobacterium <i>Hyalangium minutum</i>. Their structures were determined by 2D NMR and HR-MS/MS experiments, and their stereochemical configuration was established by a combination of NMR data, quantum mechanical calculations, and circular dichroism experiments. Hyalachelins are unusual catecholate-type siderophores that bear a 3,7,8-trihydroxy-1-oxo-1,2,3,4-tetra­hydro­isoquinoline-3-carbox­ylic acid. Their iron chelating activities were evaluated in a CAS assay showing EC₅₀ values of ∼30 μM