Functional insights into the biosynthesis of antifungal mandimycin.

BACKGROUND

Escalating fungicide resistance intensifies crop losses, demanding sustainable solutions. We report Streptomyces netropsis AK308 from Xinjiang's Ailik Lake, which produces mandimycin, a polyene macrolide whose unique C-35 dideoxysaccharide is reported to enable phospholipid targeting, thereby potentially circumventing ergosterol-based resistance mechanisms. We evaluated its efficacy against 12 key pathogens and mapped its biosynthetic gene cluster to enable future development.

RESULTS

The mandimycin mixture consisting of four congeners (A-D), showed broad-spectrum activity against 12 phytopathogens with EC₅₀ values ranging from 0.02 to 8.98 μg mL-1. It outperformed natamycin, particularly against Botryosphaeria berengeriana and Valsa ceratosperma. Genomic analysis revealed the snt biosynthetic cluster, confirmed by disrupting core PKS genes (sntM, sntNII) resulting in no production. Functional dissection revealed: (i) sntO-sntS govern atratcynose A synthesis/attachment (ΔsntO eliminated all congeners), (ii) Deletion of the regulator gene sntT abolished mandimycin production entirely, whereas inactivation of sntU, a gene putatively involved in precursor synthesis, reduced the yield by 44.7%, and (iii) overexpression of individual snt genes (A, B, T, U) consistently increased the relative abundance of monoglycosylated congeners (B/D) over fully glycosylated ones (A/C), directly identifying C-35 glycosylation as the major biosynthetic bottleneck.

CONCLUSIONS

This study identifies mandimycin as a potential agricultural antifungal agent. The validation of the snt cluster reveals the key role of C-35 glycosylation in limiting production, offering a pathway for targeted metabolic engineering to enhance yield and improve sustainable crop protection. © 2026 Society of Chemical Industry.