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Abstract
This study was carried out to evaluate the antibacterial activities of 50 strains of Streptomyces against Pseudomonas syringae P01, causing black pit disease on orange, Pectobacterium carotovorum Ecc4 causing soft rot disease on tomato, and Erwinia papayae M16 causing the soft rot disease on papaya using perpendicular streak method. The number of strains showing antagonistic activities against P. syringae P01, P. carotovorum Ecc4, and E. papayae M16 were 33, 19, and 17, respectively. Among these, the Streptomyces murinus NARZ strain showed the strongest antibacterial activities against all three pathogen bacteria. The antibacterial diameters were 20.90 ± 0.91, 23.53 ± 0.79, and 26.52 ± 0.53 mm associated with P. syringae P01, P. carotovorum Ecc4, and E. papayae M16, respectively. The tests of the heat stability (30, 60, 90 and 121oC/15 min) and pH stability (5, 6, 7, 8, 9) of the CFS obtained from S. murinus NARZ indicated that they maintained good antibacterial activities when treated at 121oC for 15 minutes and pH in the range of 5-7 for all three tested bacteria. This study implied that Streptomyces sp. synthesizes natural antibiotic compounds as biocontrol agents in the post-harvest preservation of fruits and vegetables.