Antioxidant Activity of Germicidin A and B Isolated from the Marine-Derived Streptomyces sp. SCS525

Oxidation of lipid compounds in foods reduces their shelf-life, and oxidation in living cells causes damage through the release of free radicals. Synthetic antioxidants for food preservation are phenolic in nature, and thus their use is tightly regulated. On the other hand, naturally occurring antioxidants that have been successfully isolated are limited by low efficacy and high cost. Therefore, the development of safe and low-cost natural antioxidants for use in food production and preservation is needed. Here, we investigated antioxidant activity in extracts from isolated marine bacteria derived from marine sediments. Among them, Streptomyces sp. SCS525 showed strong antioxidant activity as measured by free radical scavenging assays. Bioassay-guided fractionation and spectroscopic data analyses led to the identification of gramicidin A (1) and B (2) as strong antioxidant compounds produced by Streptomyces sp. SCS525. These two compounds are known to inhibit spore germination, and the polyketide type III pathway-related protein Gcs. These results suggest that safe and low-cost antioxidants can be produced from marine bacteria on a large scale.