Pentamycin derived from Streptomyces murinus TCS22-109 as a promising biocontrol agent against postharvest gray mold and soft rot

The majority of plant diseases are caused by pathogenic fungi, leading to huge losses in agriculture and forestry. Recently, the isolation and identification of antifungal compounds from actinomycetes have emerged as effective strategies for developing novel biological fungicides. In this study, the antagonistic strain TCS22-109 demonstrated broad-spectrum antifungal activity against six common pathogenic fungi and was identified as Streptomyces murinus based on morphological, physiological, and biochemical characteristics, as well as phylogenetic analysis of the 16S rRNA gene sequence. To tap into the bioactive potential of actinomycetes, an antifungal activity-guided isolation was performed on the fermentation extracts of strain TCS22-109. As a result, two antifungal compounds, actinomycin D and pentamycin, were isolated from TCS22-109, and their chemical structures were elucidated using NMR (nuclear magnetic resonance spectroscopy) and HR-MS (high-resolution mass spectrometry) analysis. Among these, pentamycin exhibited notable broad-spectrum antifungal properties, particularly against Rhizoctonia solani and Botrytis cinerea. Scanning electron microscopy (SEM) revealed that pentamycin inhibited the mycelial growth of B. cinerea and induced sporulation. Additionally, treatment with pentamycin led to ergosterol depletion and enhanced intracellular leakage in B. cinerea mycelium, indicating damage to cell membranes. Furthermore, pentamycin effectively protected postharvest fruit from gray mold caused by B. cinerea. These findings suggest that pentamycin derived from S. murinus TCS22-109 holds promise as a natural fungicide for managing plant and postharvest fruit diseases.