Bioactive Secondary Metabolites Produced by the Hadal Actinomycete Streptomyces sp. SY1414 Isolated from the Mariana Trench-derived Sediment

Abstract

Background:: Accumulated investigations have demonstrated that the Mariana Trench is enriched in microorganisms. However, the diversity of structures and bioactivities of the secondary metabolites produced by the Mariana Trench-associated microorganisms is poorly known, which needs to be intensively investigated. Objective:: This study aimed to investigate the bioactive secondary metabolites produced by a Mariana Trench-derived actinomycete Streptomyces sp. SY1414 was cultured in BY medium, which was chosen from four different media based on the diversity of secondary metabolites. Methods:: A combination of different column chromatographs and HPLC was applied for the separation and purification of the secondary metabolites. The structures of the isolated compounds were determined mainly based on their NMR data, optical rotation values, and the comparison with the reference data, and the Sulforhodamine B (SRB) method was used to evaluate the anti-glioma activity of isolated compounds. Results:: Four different types of compounds were isolated from the large culture of strain Streptomyces sp. SY1414 in BY medium, including a benzoquinoline alkaloid, actinophenanthroline C (1), a benzamide, (2E,4E)-5-(3-hydroxyphenyl)-penta-2,4-dienamide (2), a cyclopeptide, valinomycin (3), and four macrolides of bafilomycin D (4), bafilomycin A2 (5), bafilomycin W (6), and C(19), C(21)- O-methyl-bafilomycin A1 (7). Actinophenanthroline C (1), bafilomycin D (4), bafilomycin A2 (5), and bafilomycin W (6) displayed significant anti-glioma activities with IC50 values ranging from 1.62 to 8.20 μM for U87MG cells and 2.45 to 3.89 μM for U251. The anti-gliomas of actinophenanthroline C (1) was reported for the first time. Conclusion:: The hadal actinomycete Streptomyces sp. SY1414 in BY medium produced four different types of secondary metabolites with significant anti-glioma activity, which enriched the diversity of structures and bioactivities of the Mariana Trench-associated natural products.