Abstract:
The objectives of this study were to: isolate endophytic actinomycetes from native durian varieties in Chanthaburi and tested antimicrobial activity isolated from leaves, branches and roots using surface sterile technique, and culture on humic acid vitamin agar. All ten isolated entophytes were tested for their antimicrobial activity to Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 28753, Bacillus cereus TISTR 2372 and Staphylococcus aureus ATCC 25923. Among these, only isolate PM-R01 exhibited antibacterial activity against PM-R01 B. cereusTISTR 2372 and S. aureus ATCC 25923, with average inhibition zones of 14.33 ± 2.33 mm and 13.00 ± 1.00 mm, respectively. The crude extracted of endophytic actinomycete, PM-R01 was extracted using ethyl acetate as solvent showed texture sticky substance and brown color with a weight of 0.8767 g and yield was 0.0175%. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) value were tested by broth microdilution technique. The MIC of PM-R01 crude extract was above 1,024 µg/ml. At this concentration, the extract achieved 98% bacterial kill. Macroscopic characteristic of endophytic actinomycete PM-R01 was gray aerial mycelium. Microscopic characteristic of fiber was studied by slide culture method under the microscope. It was found that the spore lines looked like whorl and umbel, called verticillati, this was the most common in the Streptomyces genus actinomyces. PM-R01 showed closest 16S rRNA gene sequence similarity to Streptomyces diastaticus (at 99.65%). Strain KP-R01 showed the anti-Phytophthora activity, with dual culture inhibition percentages of 66.7, 61.2, and 58.9 against L04, M01, and R01, respectively. KP-R01 also exhibited anti-Phytophthora activity by volatilization, with an inhibition percentage of 33.3. Viable spores of KP-R01 exhibited strong anti-Phytophthora activity, with inhibition percentages of 98.3, 98.0, and 98.0 against L04, M01, and R01, respectively. In addition, KP-R01 produced cellulase on Carboxy methyl cellulose agar. Macroscopic characteristic of young colonies of KP-R01 were light yellow in color, with light yellow substrate mycelium and white aerial mycelium. Microscopic examination revealed hyphae with irregular branching and spore chains with coiled ends. Based on 16S rRNA gene sequencing, strain KP-R01 was identified as Streptomyces sp. and showed 99.20% similarity to Streptomyces lucensis JCM 4490 (type strain). These results suggest that the two endophytic actinomycete isolates, PM-R01 and KPR01, have potential for microbial control and may be further developed into other biological substances for various benefits.