BLAST search revealed that the 16S rRNA sequence of the strain RK88-1441 could belong to the actinomycete genus, Streptomyces. This strain, Streptomyces sp. RK88-1441,5 was maintained on media consisting of soluble starch 10 g, yeast extract 1 g, NZ-amine 1 g and agar 15 g in 1.0 l of distilled water, pH 7.0. The stock culture was inoculated into 100 ml test tubes containing 10 ml of seed medium, which was of the same composition as above, but without agar. The test tubes were incubated on a rotary shaker (165 r.p.m.) at 28 °C for 48 h. Each of the seed medium samples was transferred to 10 l of production medium (glucose 2%, soluble starch 1%, meat extract 0.3%, dried yeast 0.25%, K2HPO4 0.005%, NaCl 0.05%, CaCO3 0.05% and MgSO4 × 7H2O 0.05%) in the 500 ml of cylindrical flask (K1 flask) containing 70 ml. Fermentation was carried out at 28 °C for 6 days under shaking conditions (155 r.p.m.), after which the supernatant and mycelium were separated by centrifugation. The culture supernatant was extracted with ethyl acetate and the mycelium was extracted with acetone. After concentrating the ethyl acetate and acetone-soluble portions under reduced pressure, the two portions were combined and dried to yield 1.6 g of extract. The dried extract was then separated by silica gel column chromatography (CHCl3–MeOH, gradient 50:1–0:1 (v/v)) into seven fractions. Fraction 6 was further purified by C18-HPLC (Senshu Pak Pegasil column (Tokyo, Japan), 5 μm, 20 mm i.d. × 250 mm) with isocratic elution using methanol/water (20:80) to yield compounds 1 (4.1 mg), 2 (2.5 mg) and 3 (1.8 mg).

Compounds 1, 2 and 3 were evaluated for cytotoxic activity against human cervical cancer cells (HeLa), human promyelocytic leukemia cells (HL-60), mouse temperature-sensitive cdc2 mutant cells (tsFT210) and rat kidney cells that were infected with ts25 (srcts-NRK). They were also evaluated for antimicrobial activity against Staphylococcus aureus, Escherichia coli, Aspergillus fumigatus, Pyricularia oryzae and Candida albicans, and for antimalarial activity against Plasmodium falciparum. Compound 2 showed weak antimalarial activity (IC50 value of 15 μg ml−1) without any cytotoxicity. Compounds 1 and 3 did not show any effect in any of the above assays when tested at concentrations up to 30 μg ml−1.

Log in or create a free account to read this content

Gain free access to this article, as well as selected content from this journal and more on nature.com

Access through your institution

or

Sign in or create an account
Continue with Google
Continue with ORCiD