Oligomycin A from Streptomyces paludis: potent antifungal activity against Colletotrichum truncatum and control of soybean anthracnose.

BACKGROUND: Soybean anthracnose caused by Colletotrichum truncatum is a destructive disease threatening soybean production. Increasing fungicide resistance and concerns over chemical residues highlight the need for new antifungal agents with distinct bioactive scaffolds. This study aims to identify the antifungal metabolite produced by Streptomyces paludis 13-3 and evaluate its potential for soybean anthracnose management RESULTS: Bioassay-guided fractionation of the fermented extract of S. paludis 13-3 led to the isolation of oligomycin A, characterized via nuclear magnetic resonance spectroscopy and high-resolution electrospray ionization mass spectrometry. It exhibited half-maximal effective concentration (EC50) values of 0.0173 μg mL-1 and 0.0811 μg mL-1 against mycelial growth and conidial germination of C. truncatum, respectively. Its antifungal potency was approximately 58 times more potent than difenoconazole. At a concentration of 1 μg mL-1, oligomycin A achieved 85.85% control efficacy against soybean anthracnose on detached seedlings without inducing phytotoxicity, and inhibited eight tested phytopathogens by 61.69-83.39% at 0.1 μg mL-1. Fluorescence staining and scanning electron microscopy observations indicated intracellular reactive oxygen species (ROS) accumulation and significant structural damage in C. truncatum treated with oligomycin A.

CONCLUSION: This study provides the first evidence that oligomycin A exhibits strong antifungal activity against C. truncatum and effectively suppresses soybean anthracnose development in detached seedlings. These findings expand the known antifungal spectrum of oligomycin A and highlight its value as a natural lead compound for the development of antifungal agents against soybean anthracnose. © 2026 Society of Chemical Industry.