Peschel, G. | Search bioRxiv

bioRxiv2024

Spirolactone, an unprecedented antifungal β-lactone spiroketal macrolide from Streptomyces iranensis

Fungal infections pose a great threat to public health and there are limited antifungal medicaments. Streptomyces is an important source of antibiotics, represented by the clinical drug amphotericin B. The rapamycin-producer Streptomyces iranensis harbors an unparalleled Type I polyketide synthase, which codes for a novel antifungal macrolide alligamycin A (1), the structure of which was confirmed by NMR, MS, and X-ray crystallography. Alligamycin A harbors an undescribed carbon skeleton with 13 chiral centers, featuring a ({beta}-lactone moiety, a [6,6]-spiroketal ring, and an unprecedented 7-oxo-octylmalonyl-CoA extender unit incorporated by a potential novel crotonyl-CoA carboxylase/reductase. The ali biosynthetic gene cluster was confirmed through CRISPR-based gene editing. Alligamycin A displayed profound antifungal effects against numerous clinically relevant filamentous fungi, including Talaromyces and Aspergillus species. ({beta}-Lactone ring is essential for the antifungal activity and alligamycin B (2) with disruption in the ring abolished the antifungal effect. Proteomics analysis revealed alligamycin A potentially disrupted the integrity of fungal cell walls and induced the expression of stress-response proteins in Aspergillus niger. Alligamycins represent a new class of potential drug candidate to combat fungal infections.

biochemistry↗

bioRxiv2022

Streptomyces alleviate abiotic stress in plant by producing pteridic acids

Soil microbiota can confer fitness advantages to plants and increase crop resilience to drought and other abiotic stressors. However, there is little evidence on the mechanisms correlating a microbial trait with plant abiotic stress tolerance. Here, we report that Streptomyces effectively alleviates the drought and salinity stress by producing spiroketal polyketide pteridic acid H (1) and its isomer F (2), both of which promote root growth in Arabidopsis at a concentration of 1.3 nM under abiotic stress. Pteridic acids induce stress response genes expression in salinity-stressed Arabidopsis seedlings. The bifunctional biosynthetic gene cluster of pteridic acids and antimicrobial elaiophylin is confirmed in vivo and mainly disseminated by vertical transmission which is geographically distributed in various environments. This discovery reveals a perspective for understanding plant-Streptomyces interactions and provides a promising approach for utilising beneficial Streptomyces and their secondary metabolites in agriculture to mitigate the detrimental effects of climate change.

microbiology↗