Antioxidant and cytotoxic activities of metabolites produced by a new marine Streptomyces sp. isolated from the sea cucumber Holothuria leucospilota

Marine microorganisms are important sources for novel natural products. Hence, the aim of this study was to introduce marine microorganisms with the capability of producing antioxidant and cytotoxic metabolites. For this purpose, ten live sea cucumbers (Holothuria leucospilota) were collected from Larak Island, Persian Gulf. Then, their intestine contents were serially diluted and treated by heating (55°C). 100 µL of treated samples were inoculated on starch casein nitrate agar medium, which is supplemented with nalidixic acid and cycloheximide. The plates were incubated at 28 °C for 4 weeks and the colonies were purified. The antioxidant activity of extracted metabolites from the isolated actinobacteria was evaluated using DPPH (1,1-diphenyl-2-picrylhydrazyl) radical scavenging activity assay and the cytotoxic activity was screened by Brine-Shrimp micro well cytotoxicity method. In addition, the cytotoxic effect was evaluated against HCT 116 and SW 480 cell lines by MTT cell proliferation assay. A new strain of marine actinobacterium represented maximum antioxidant and cytotoxic activity among 17 actinobacterial isolates. The ethyl acetate culture extract of the isolate scavenged DPPH radicals with IC50 value of 211.2 µg mL-1. In addition, the extract exhibited high toxicity against HCT 116 and SW 480 tumor cell lines with IC50 values of 26.48 and 18.53 µg mL-1 respectively. The isolate was identified as Streptomyces sp. strain SC 156 and showed 98% similarity with type strains in NCBI database. These results suggested that Streptomyces sp. strain SC 156 could be considered as promising candidate for antioxidant and cytotoxic compound discovery.