To find bioactive natural products, the ethyl acetate extract of Streptomyces cacaoi subsp. asoensis H2S5 was analyzed based on molecular networking. The analysis targeted a specific cluster and led to the discovery of two unprecedented rearranged ansamycins incorporating a fused 5/6/7 tricyclic ring system, strecacansamycins A (1) and B (2), and one rare glycosylated trienomycin, strecacansamycin C (3). Their structures were determined by comprehensive NMR analysis, ECD calculations, chemical reactions, and enzyme stereospecificity analysis. The genome of the produced strain was sequenced and the related gene cluster (tym) was identified. With the availability of the genome sequence data, the known stereospecificities of biosynthetic enzymes provided more evidence for the absolute stereochemistry identification. Anti-proliferative assays revealed that strecacansamycin A (1) exhibited significant activity with the IC₅₀ values of 2.21, 0.61, and 7.01 μM against PC-3, HepG2, and U87-MG cells, respectively.

Thioamidated ribosomally synthesized and post-translationally modified peptides (RiPPs) are recently characterized natural products with wide range of potent bioactivities, such as antibiotic, antiproliferative, and cytotoxic activities. These peptides are distinguished by the presence of thioamide bonds in the peptide backbone catalyzed by the YcaO-TfuA protein pair with its genes adjacent to each other. Genome mining has facilitated an in silico approach to identify biosynthesis gene clusters (BGCs) responsible for thioamidated RiPP production. In this work, publicly available genomic data was used to detect and illustrate the diversity of putative BGCs encoding for thioamidated RiPPs. AntiSMASH and RiPPER analysis identified 613 unique TfuA-related gene cluster families (GCFs) and 797 precursor peptide families, even on phyla where the presence of these clusters have not been previously described. Several additional biosynthesis genes are colocalized with the detected BGCs, suggesting an array of possible chemical modifications. This study shows that thioamidated RiPPs occupy a widely unexplored chemical landscape.

The ethyl acetate extract from the liquid fermentation of S. caelestis Aw99c exhibited high and broad antifungal activities against plant pathogenic fungi. Bioassay guide fractionation led to the discovery of two xanthones, citreamicin ε and θ. The draft genome sequence of S. caelestis Aw99c was analyzed by a similarity-based approach to elucidate the pathway for the citreamicins. A 48 kb citreamicin (cit) gene cluster with 51 open reading frames encoding type II polyketide synthases and unique polyketide tailoring enzymes was proposed based on the genome analysis and the chemical structure derivation. In vitro antifungal assay showed that citreamicin ε exhibited significant growth inhibition against the plant pathogenic fungi with MIC values ranging from 1.56 to 12.5 μM. The cellular structural change of M. grisea treated with citreamicin ε was detected by SEM and the result showed that citreamicin ε caused disruptive surface of the mycelia.