Abstract: By using various sorts of column chromatography,ten compounds were isolated from the bioactive fraction of Streptomyces antibioticus strain H12-15 which derived from the sea bed mud at the mangrove district of South China Sea.The structures of these compounds were identified as actinomycin X2(1), actinomycin D(2), lanosterol(3), 4,4-dimethylzymosterol(4),ergosterol peroxide(5),24-methyl-5α-cholesta-7,22-diene-3β,6α-diol(6),3β,5α,9α-trihydroxy ergosta-7,22-diene-6-one(7),3β,5α,9α,14α-tetrahydroxyergosta-7,22-diene-6-one(8),5α,6α-epoxy ergosta-8,14,22-triene-3β,7α-diol(9),β-sitosterol(10) based on the spectroscopic analysis.Among them,compounds 3-10 were isolated from Streptomyces species for the first time.Cytotoxicities of these compounds against cancer cell lines were evaluated in vitro by MTT assay.Among them,compounds 1 and 2 showed significant growth inhibition of tumor cells,with IC₅₀ values lower than 1.6 μg/mL,and compound 9 exhibited mild cytotoxic activity.

Key words: Streptomyces antibioticus, mangrove, metabolites, actinomycin, sterols