Environment and Natural Resources Journal (Jun 2022)
Diversity and Antimicrobial Activity of Plant Growth Promoting Endophytic Actinomycetes Isolated from Thai Orchids
Abstract
Thirty-two endophytic actinomycetes isolated from 15 Thai orchids were taxonomically studied based on their phenotypic characteristics and 16S rRNA gene sequence analyses (98.97-100.00%). The isolates were identified as Streptomyces including S. parvulus (3 isolates), S. tendae (2 isolates), S. ardesiacus (2 isolates), S. heilongjiangensis (2 isolates), and each of S. daghestanicus, S. antibioticus, S. malaysiensis, S. deserti, S. spiralis, S. thermoviolaceus subsp. apingens, S. globosus, S. collinus, S. olivaceus, and S. zaomyceticus. Micromonospora including M. humi (2 isolates), M. maritima (2 isolates), and each of M. tulbaghiae, M. schwarzwaldensis, M. chersina, M. chalcea M. citrea, and M. aurantiaca; Streptosporangium (2 isolates) including S. sandarakinum and S. pseudovulgare and an isolate of Actinomadura hibisca. Streptomyces (7 isolates), Micromonospora (7 isolates), and Streptosporangium (1 isolate) exhibited antimicrobial activity against Bacillus subtilis ATCC 6633, Kocuria rhizophila ATCC 9341, Staphylococcus aureus ATCC 25923, Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853, and Candida albicans ATCC 10231. Indole-3-acetic acid (IAA) production of the isolates ranged from 0.04 to 67.30 µg/mL. Isolates DR10-1 and DR9-7 produced high amounts of IAA (58.03 and 67.30 µg/mL) and were selected for optimization. Maximum IAA values obtained were 284.87 and 132.35 µg/mL, using 0.4% L-tryptophan and pH 7 with incubation at 30°C for 13 days. These two isolates enhanced root length, shoot length, number of roots, and fresh weight of rice seedlings (Oryza sativa L. cv. RD49) compared to the control. Results indicated that actinomycetes from Thai orchids were promising sources of antimicrobial compounds and plant hormones for agricultural applications.
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