Discovery of Antibacterial Compounds against Xanthomonas citri subsp. citri from a Marine Fungus Aspergillus terreus SCSIO 41202 and the Mode of Action.

Citrus canker, caused by Xanthomonas citri subsp. citri ( Xcc ), is a severe citrus disease. Currently, copper-containing pesticides are widely used to manage this disease, posing high risks to the environment and human health. This study reports the discovery of naturally occurring anti- Xcc compounds from a deep-sea fungus, Aspergillus terreus SCSIO 41202, and the possible mode of action. The ethyl acetate extract of A. terreus was subjected to bioassay-guided isolation, resulting in the discovery of eight anti- Xcc compounds ( 1 - 8 ) with minimum inhibitory concentrations (MICs) ranging from 0.078 to 0.625 mg/mL. The chemical structures of these eight metabolites were determined by integrative analysis of various spectroscopic data. Among these compounds, Asperporonin A ( 1 ) and Asperporonin B ( 2 ) were identified as novel compounds with a very unusual structural skeleton. The electronic circular dichroism was used to determine the absolute configurations of 1 and 2 through quantum chemical calculation. A bioconversion pathway involving pinacol rearrangement was proposed to produce the unusual compounds ( 1 - 2 ). Compound 6 exhibited an excellent anti- Xcc effect with a MIC value of 0.078 mg/mL, which was significantly more potent than the positive control CuSO ₄ (MIC = 0.3125 mg/mL). Compound 6 inhibited cell growth by disrupting biofilm formation, destroying the cell membrane, and inducing the accumulation of reactive oxygen species. In vivo tests indicated that compound 6 is highly effective in controlling citrus canker disease. These results indicate that compounds 1 - 8 , especially 6 , have the potential as lead compounds for the development of new, environmentally friendly, and efficient anti- Xcc pesticides.