Quinolinone and Amicoumacin Derivatives From the Deep Sea‐Derived <i>Bacillus rugosus</i> SCSIO 41395 and Their Bacteriostatic Activities Against <i>Pseudomonas aeruginosa</i>

Two new natural 2-alkylquinolin-4(1H)-one derivatives, 2-(5-methylheptyl) quinolin-4(1H)-one (1) and 2-(5-methylnonane) quinolin-4(1H)-one (2), along with ten known compounds (3-12), were isolated from the strain of Bacillus rugosus SCSIO 41395, which was obtained from the sediments of the Philippine Basin. All the isolates were evaluated for bacteriostatic activities against Pseudomonas aeruginosa (PA). Compounds 4 and 5 exhibited bacteriostatic effects by inhibiting the expression of rhl, pqs, and las quorum-sensing genes, as well as suppressing related phenotypes, including rhamnolipid, pyocyanin production, and biofilm formation. Our findings suggest that compounds 4 and 5 are promising quorum-sensing inhibitors for potential alternative treatments of PA infections.