Exploring the biocontrol potential of Streptomyces sp. B2008 through mechanistic insights into the antifungal effect of actinomycin D

• Streptomyces sp. B2008 improved the growth of banana plantlets. • The antagonistic activity of strain B2008 against Foc TR4 was associated with actinomycin D. • Actinomycin D was able to regulate cell-wall related genes in Foc TR4. Our previous study revealed that a mangrove-sediments derived actinomycete, Streptomyces sp. B2008, could produce antibiotic actinomycin D and effectively inhibit the growth of Fusarium oxysporum f. sp. cubense tropical race 4 ( Foc TR4) , the most destructive pathogen of banana worldwide. Here, the growth rate of banana plants was significantly accelerated after the application of strain B2008. Actinomycin D isolated from the strain displayed potent antifungal activity against Foc TR4 with an EC 50 value of 26μg mL −1 that may contribute to its antagonist activity. Transcriptomic and molecular docking analysis revealed that actinomycin D was able to regulate gene expressions of FOIG_09283, FOIG_02707 and FOIG_05942 in Foc TR4 . Deletion of these genes led to phenotype featured with severe defects in hyphae growth and colony morphology, while weakening environmental stress tolerance. Furthermore, lack of FOIG_02707 and FOIG_05942 showed a defect in conidiation and remarkably affected the pathogenicity of Foc TR4. These findings suggested that actinomycin D inhibited Foc TR4 by affecting expression of FOIG_02707 and FOIG_05942 , further confirming the application potential of Streptomyces sp. B2008 as a biological control agent.