Overexpression of PPtase in Streptomyces sp. NAUS: Increasing biocontrol potential against postharvest tomato fruit decay and isolation of a novel antifungal compound

Streptomyces species are considered promising biological control strains since they produce various antimicrobial substances to control diseases in fruit and vegetables. Many Streptomyces species' biosynthetic gene clusters (BGCs) are silent when subjected to conventional laboratory conditions. Therefore, activating these BGCs is crucial for developing effective strategies for controlling postharvest phytopathogens. In the present study, phosphopantetheinyl transferase (PPtase) genes were overexpressed in 20 actinomycetes isolated from the soil rhizosphere of Osmanthus fragrans to trigger cryptic BGCs. The genomic comparison between the highly proficient actinomycete (strain NAUS) and Streptomyces albiflaviniger DSM 42598T yielded an average nucleotide identity (ANI) exceeding 95%, indicating that the strain belongs to the same species. The NAUS - PPtase-overexpressed strain exhibited 4.7 times higher antifungal activity than the wildtype strain against Penicillium citrinum. Its fermented extracts remarkably reduced postharvest tomato fruit decay by 89.71%. A novel ionophore compound with outstanding antimicrobial activity was identified based on spectroscopic and chemical methods. The enhanced antifungal activities and biocontrol efficacy can be attributed to activated secondary metabolites in the PPtase-overexpressed S. albiflaviniger strain, highlighting the usefulness of this pipeline for biocontrol of pathogenic fungi and bacteria.