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 introducing the marine microorganisms with capability to produce antioxidant and cytotoxic metabolites. For this purpose, ten live sea cucumbers (Holothuria leucospilota) were collected from Larak Island. 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, 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 was evaluated using DPPH radical scavenging activity and the cytotoxic activity of the isolates was screened by Brine-Shrimp micro well Cytotoxicity method. In addition, cytotoxic effect of potent crude extract was evaluated against HCT 116 and SW 480 cell lines by MTT cell proliferation assay. A new strain of marine actinobacterium was isolated with maximum antioxidant and cytotoxic activity among 17 marine actinobacterial isolates. The crude extract of the isolate scavenged DPPH radicals with IC50 value of 211.2 µg/ml. MTT cell proliferation assay revealed that the extract exhibited high toxicity against HCT 116 and SW 480 cell lines with IC50 values of 26.48 and 18.53 µg/ml respectively. The isolate identified as Streptomyces sp. strain SC 156 with 98% similarity in NCBI database. These results suggested that isolated Streptomyces sp. strain SC 156 could be considered as promising candidates for antioxidant and cytotoxic compound discovery.