Antimicrobial, antitumor and in vivo cytotoxicity of actinomycetes inhabiting marine shellfish

Sixty-three actinomycete strains isolated from the marine shellfish Donax trunculus anatinus were phenotypically identified as ten genera, in addition to two unidentified strains. Their metabolic extracts exhibited wide antimicrobial activities towards 11 reference and clinical cultures; and 17.5% showed antitumor activities with solid tumor selectivity of four Nocardioides, Kitasatosporia and Streptomyces strains. Streptomyces 23-2B was particularly noted for its high antitumor activity against Ehrlich’s ascites carcinoma with plateau inhibitory effect at 500, 250 and 50 μg/ml concentrations, promising solid tumor selectivity and high cytotoxicity to human carcinoma of liver (HEPG2), cervix (HELA) and breast (MCF7) (IC₅₀: 3.89, 9.4 and 10 μg/ml, respectively). In vivo cytotoxicity of S.23-2B metabolites showed common sign of unimpaired kidney and liver functions, as indicated from non-significant elevation in serum enzymatic activities, urea, creatinine, total protein and albumin levels in response to 0.5 and 5 μg/g doses after alternate-day injection for 2 weeks. Microorganisms associated with the marine shellfish are suggested to be potential source of bioactive metabolites.