LC-MS-Based Annotation of Bioactive Metabolites From Streptomyces fimicarius-ghR Against the Common Scab Pathogen...

Natural products have long served as a cornerstone for the discovery of antimicrobial drugs. Members of the genus Streptomyces are particularly noteworthy for their ability to produce structurally diverse metabolites, occupy diverse ecological niches, and enhance soil nutrient availability in agricultural systems. They also represent a major reservoir of antibiotics with strong antagonistic activity against plant pathogens. In an ongoing study, Streptomyces fimicarius-ghR demonstrated antimicrobial activity, particularly against the potato common scab pathogen (Streptomyces sp.). To elucidate the chemical basis underlying its biocontrol efficacy, we employed a computational metabolomics-based bioprospecting strategy to characterize the chemical diversity of potential anti-scab metabolites in the antagonist's fermentation broth. The ethyl acetate (EtOAc) extract of S. fimicarius-ghR exhibited inhibitory activity against Streptomyces sp. FG1, with a minimum inhibitory concentration (MIC) of 0.3 mg/mL. The EtOAc extract was subjected to liquid chromatography-quadrupole time-of-flight tandem mass spectrometry (LC-QTOF-ESI-MS/MS), followed by molecular networking-based data analysis. This approach enabled the annotation of 13 metabolites, including multiple isomers of mycosubtilins as well as both linear and cyclic surfactins. These findings suggest that lipopeptide antibiotics, particularly surfactins and mycosubtilins produced by S. fimicarius-ghR, may play a central role in suppressing the potato common scab pathogen.