Antibacterial and Cytotoxic Metabolites Produced by Streptomyces tanashiensis BYF-112 Isolated from Odontotermes formosanus

Chemical investigations of termite-associated Streptomyces tanashiensis BYF-112 led to the discovery of four new alkaloid derivatives, vegfrecines A and B ( 1 and 2 ), exfoliazone A ( 3 ), and venezueline H ( 7 ), along with nine known metabolites ( 4 - 6 , 8 - 13 ). Their structures were determined by spectroscopic data analysis and compared with those reported. The antibacterial bioassay indicated that viridomycin A ( 11 ) showed strong antibacterial activity against Staphylococcus aureus with a zone of inhibition (ZOI) value of 12.67 mm, compared to that of the positive gentamicin sulfate with a ZOI value of 17.67 mm. Viridomycin A ( 11 ) also exhibited moderate antibacterial activity against Micrococcus tetragenus and Pseudomonas syringae pv. actinidae with the ZOI values of 15.50 and 14.33 mm, which was weaker than those of positive gentamicin sulfate with the ZOI value of 34.67 and 24.00 mm, respectively. Besides, viridomycin F ( 12 ) exhibited moderate antibacterial effects against S. aureus, M. tetragenus and P. syringae pv. actinidae with the ZOI values of 8.33, 16.50, and 10.83 mm, respectively. Moreover, the cytotoxic bioassay showed that viridobruunine A ( 5 ), exfoliazone ( 6 ), viridomycin A ( 11 ), and X-14881E ( 13 ) displayed significant cytotoxicity against human malignant melanoma cell lines (A375), human ovarian cancer cell lines (SKOV-3), and human gastric cancer cell lines (MGC-803) with the IC₅₀ values ranging from 4.61-19.28 μM. Additionally, a putative biosynthetic gene cluster (BGC) responsible for compounds 1 - 12 was proposed using bioinformatic analysis of the full genome of S. tanashiensis. The secondary metabolites of insect-associated S. tanashiensis BYF-112 might be a potential source to exploit the novel antibacterial and anticancer agents.