Discovery of Virulence Attenuator of Chromobacterium violaceum CV026 From Marine-Derived Fungus Aspergillus ochraceus LSD-13 by Inhibiting Quorum Sensing and Destroying Biofilm.

Targeted quorum-sensing (QS) represents a promising approach to combat multidrug-resistant infections. In this study, an undescribed pyrazine derivative 5-isobutyryl-1,4-dihydropyrazine-2,3-dione (1) together with three known compounds (2--4) were isolated from the marine-derived fungus Aspergillus ochraceus LSD-13. Compound 2 was a potent virulence attenuator of Chromobacterium violaceum CV026 with a minimum inhibitory concentration (MIC) of 32 µg/mL. At sub-MIC, compound 2 significantly suppressed the production of QS-controlled phenotypes: violacein, N-acyl homoserine lactone, chitinase, and extracellular polysaccharide. It also reduced biofilm formation by 73.3% at 1/2 MIC, a phenotype confirmed by scanning electron microscopy. Furthermore, compound 2 inhibited swarming motility in a dose-dependent manner. Mechanistic investigations revealed that compound 2 downregulated the expression of QS-associated genes (cviR, vioA, vioC). Molecular docking demonstrated that compound 2 has a strong binding affinity for CviR protein with -6.8 kcal/mol, suggesting a competitive antagonism of the native C6HSL ligand. These findings highlight compound 2 as a promising QS inhibitor with therapeutic potential against C. violaceum CV026.