Objective: To investigate the antimicrobial and cytotoxic activities of bioactive compounds produced by Streptomyces sp. KB1 isolated from the air sample at Ao-nang, Krabi province, Thailand.

Methods: Streptomyces sp. KB1 was identified by 16S rDNA gene sequencing. It was preliminarily investigated the antibacterial activity by cross streak method and then cultivated in the half-formula of Luria Bertani at 30 C, 200 rpm in shaking incubator for 7 d. Culture broth of each day was prepared as cell-free culture broth and tested the anti-Staphylococcus aureus TISTR 517 activity by agar well diffusion method along with determined the protein concentration by Bradford assay. Bioactive compounds were assessed the antimicrobial activity and cytotoxicity against brine shrimp by broth microdilution method and brine shrimp lethality bioassay, respectively.

Results: Bioactive compounds were excreted into liquid culture medium within 2 d of cultivation and showed a broad spectrum of antibacterial activity. Whereas, the highest activity has shown since day 4th of an incubation period which had protein concentration equal 254±3.1 µg/ml. Bioactive compounds showed strong activity against Gram-positive bacteria, moderate activity against Gram-negative bacteria and weak activity against yeasts and Pseudomonas aeruginosa TISTR 1467. The MIC, MBC or MFC, and LC50

Conclusion: This study implied that bioactive compounds produced by Streptomyces sp. KB1 may be the important polypeptide compound that can be used as lead compounds for novel drug discovery. value of bioactive compounds were in the range of 0.49-63.50, 0.49-127.00, and 131.58 µg/ml, respectively.