Bioactive metabolites from the endophytic fungus Epicoccum sorghinum QA-20 isolated from Artemisia argyi with antibacterial activity against aquaculture pathogens and antioxidant potential

Artemisia argyi H. Lév. & Vaniot, an Asteraceae family herb, is extensively used in traditional Chinese pharmacopoeia and is a major local crop in Qichun County, possessing notable medicinal, economic, and cultural value. Its associated endophytes represent promising microbial candidates for natural product discovery. To investigate this potential, 40 fungal strains were isolated from A. argyi, and 12 with distinctive colony morphology were selected for scaled-down fermentation. Their EtOAc extracts were subsequently evaluated using HPLC, TLC, and antibacterial assays. Strain Epicoccum sorghinum QA-20, which displayed notable antibacterial effects, was chosen for further chemical investigation. Chromatographic separation from fermented broth extract yielded one previously undescribed polyketide, 7-methoxy-4,9-dimethyldibenzo[ b,e ][1,4]dioxin-2-ol ( 1 ), together with 12 known compounds ( 2 – 13 ). Structural elucidation was performed using NMR and/or mass spectrometry. Further structural confirmation of compound 1 was achieved through X-ray crystallographic analysis. All isolated compounds were investigated for antibacterial and antioxidant activities. Compounds 5 – 7 were effective in suppressing growth of pathogenic microbes, while compounds 1 , 6 , and 7 exhibited significant free radical scavenging activity. Compound 6 exhibited the broadest antibacterial spectrum, inhibiting all seven tested strains (MICs = 12.5–100 μ g/mL); while compound 7 exhibited DPPH (2,2-diphenyl-1-picrylhydrazyl) and ABTS (2,2’-azino-bis) scavenging capacity (IC 50 =15.81 ± 0.52and 32.95 ± 0.72 μ g/mL, respectively), comparable to that of vitamin C (IC 50 = 11.62 ± 0.85 and 28.09 ± 1.40 μ g/mL, respectively). This study demonstrates that endophytes derived from A. argyi are a valuable source of novel antibacterial and antioxidant natural products. • 40 endophytic fungi were isolated from Artemisia argyi . • Secondary metabolites of Epicoccum sorghinum QA-20, exhibiting strong antibacterial activity, were investigated. • One previously undescribed polyketide and 12 known compounds were identified. • Antibacterial and antioxidant assays identified two key bioactive leads: compound 6 (antibacterial) and compound 7 (antioxidant).