Discovery, Identification, and Mode of Action of Phenolics from Marine-Derived Fungus Aspergillus ustus as Antibacterial Wilt Agents.

The bacterial wilt caused by Ralstonia solanacearum seriously affects crop yield and safety and is difficult to control. Biological activity-guided screening led to the isolation of 11 phenolic compounds including three undescribed compounds (carnemycin H-I and stromemycin B) from the secondary metabolites of a marine-derived Aspergillus ustus . One new compound is an unusual phenolic dimer. Their structures were elucidated by comprehensive spectroscopic data and J -based configurational analysis. The antibacterial activities of the isolated compounds against R. solanacearum were evaluated. Compound 3 exhibited excellent inhibitory activity with an MIC value of 3 μg/mL, which was comparable to that of streptomycin sulfate. Additionally, 3 significantly changed the morphology and inhibited the activity of succinate dehydrogenase (SDH) to interfere with the growth of R. solanacearum . Molecular docking was conducted to clarify the potential mechanisms of compound 3 with SDH. Further in vivo experiments demonstrated that 3 could remarkably inhibit the occurrence of bacterial wilt on tomatoes.