Six new 9H-carbazole derivatives (1–6) and nine previously reported compounds
(7–15) were isolated from a fermented
solid
medium of the Thailand mangrove-derived Streptomyces strain, OUCMDZ-5511, under fluoride stress. Compounds 2–5, 12, and 15 were
exclusively present in the fluoride-supplemented fermentation medium,
while compounds 7–9, 13, and 14 were newly discovered natural products. The
molecular structures of the compounds were identified by a spectroscopic
analysis. The new compound 2 displayed antiquorum sensing
activity against Chromobacterium violaceum ATCC 12472 by reducing the violacein production and inhibiting the
biofilm formation in a concentration-dependent manner. The study revealed
that compound 2 could be a novel potential inhibitor
of quorum sensing.