Antifungal metabolites from Myxococcus stipitatus GXUA 01510 for the control of sugarcane Pokkah boeng disease caused by Fusarium sacchari

Abstract

Four previously undescribed phenyl polyenes, prophenalamides D-E (1–2) and phenalamides F-G (3–4), along with nine known compounds (5–13), were isolated from the fermentation extract of Myxococcus stipitatus GXUA 01510. Compounds 10–13 have not previously been reported from myxobacteria. The structures of these compounds were elucidated using HR-ESI-MS, and NMR spectroscopic analyses. The antifungal experiment revealed that the thiazole compounds cystothiazole A (7) and melithiazol F (9) exhibited significant activity against Fusarium sacchari strains FS-9DF-3-2 and FS-2-1, an agricultural pathogen associated with sugarcane Pokkah boeng disease. Cystothiazole A (7) significantly inhibited spore germination, displaying EC₅₀ values of 1.00 µg mL⁻¹ against FS-9DF-3-2 and 0.67 µg mL⁻¹ against FS-2-1. Regarding mycelial growth, it exhibited EC₅₀ values of 3.01 and 9.71 µg mL⁻¹ for the two strains. Remarkably, unlike the positive control and many other antifungal natural products, cystothiazole A (7), which is a rare trait among existing agents, exhibits a distinctive ability to suppress spore germination. Similarly, melithiazol F (9) inhibited mycelial growth, with EC₅₀ values of 2.94 and 1.08 µg mL⁻¹ against FS-9DF-3-2 and FS-2-1, respectively. Furthermore, both cystothiazole A (7) and melithiazol F (9) significantly increased nucleic acid and protein leakage in F. sacchari spores, highlighting their potential to disrupt cell membrane integrity. These findings not only enrich the chemical diversity of myxobacterial metabolites but also provide promising molecular scaffolds for developing novel biocontrol agents.