Biologically Active Volatile Organic Compounds (VOCs) Produced by Rhizospheric Actinobacteria Strains Inhibit the Growth of the Phytopathogen Colletotrichum musae

The antifungal potential of volatile organic compounds (VOCs) produced by actinobacterial strains Streptomyces sp. (ACTB-77) and Amycolatopsis sp. (ACTB-290) from the rhizosphere of Caatinga plants against Colletotrichum musae was investigated. VOCs produced by these microorganisms (axenic and co-culture) were investigated using headspace-solid phase microextraction (HS-SPME) and gas chromatography-mass spectrometry (GC-MS). Although no exclusive VOC peaks were observed in the co-culture with ACTB-77, the same experiment involving ACTB-290 yielded five new peaks, including two identified alcohols, suggested as bioreductive products of the corresponding ketones by the fungus. Statistical analysis revealed that co-culture ACTB-77/C. musae has a closer similarity to the fungus than to the actinobacteria, while the co‑culture ACTB-290/C. musae showed closer similarity to the actinobacteria. These confirmed the more pronounced antifungal activity of the ACTB-290 strain, as observed in the fungus growth inhibition experiments. The antifungal activity of ACTB-290 was associated to its sulfur-containing metabolites, while linalool was suggested as responsible for the ACTB-77 activity.