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.
Chemical fungicides are widely used in the agriculture sector and cause severe environmental problems. Biological control, a method using antagonistic organisms, has been considered one of the most promising strategies to tackle this issue. Actinomycetes, particularly Streptomyces strains, produced diverse classes of bioactive secondary metabolites. In this study, four Streptomyces strains, DR5-1, DR7-3, DR8-5, and DR8-8, isolated from three Dendrobium species (Orchidaceae), exhibited significant antifungal activity against five phytopathogenic fungi, particularly with high potency against Curvularia oryzae. The bacterial identification was performed based on phenotypic and chemotaxonomic characteristics, including the 16S rRNA gene sequence. Strain DR7-3 from the roots of Dendrobium findlayanum exhibited high antifungal activity, and its culture filtrate caused damage to the cell structure of C. oryzae SA04. It was identified as Streptomyces solisilvae based on the average nucleotide identity, ANIb (98.49%), and DNA-DNA hybridization value (88.40%). The EtOAc extract from strain DR7-3 was analyzed by the gas chromatography-mass spectrometry method. Among the 15 identified compounds, eicosane, phenol-2,4-bis(1,1dimethylethyl), hexadecane, and hexadecanoic acid-methyl ester showed significant antifungal activity. The draft genome sequence analysis of strain DR7-3 revealed 72 putative biosynthetic gene clusters of secondary metabolites. The genome alignment indicated that 13 gene clusters are involved in the biosynthesis of these antifungal metabolites. These results suggested that strain DR7-3 could be a promising candidate for developing new and safe microbial biological control agents for application in agricultural fields.
A novel actinomycete strain, JA03T, belonging to the genus Streptomyces , was isolated from the rhizosphere of Barringtonia racemosa (L.) Spreng. It was characterized taxonomically using a polyphasic approach. It grew at 25–37 °C, at pH 5–10 and with 6 % (w/v) NaCl. It contained ll-diaminopimelic acid in the cell-wall peptidoglycan. Ribose and glucose were detected in its whole-cell hydrolysate. The predominant cellular fatty acids were iso-C16 : 0, anteiso-C15 : 0, C16 : 0, iso-C14 : 0 and iso-C15 : 0. Detected polar lipids were phosphatidylethanolamine, diphosphatidylglycerol, phosphatidylglycerol, phosphatidylinositol, phosphatidylinositol mannosides, unidentified phospholipids and unidentified amino lipids. Based on the results of 16S rRNA gene sequence analyses, strain JA03T showed highest similarity to Streptomyces filipinensis NBRC 12860T (98.76 %), Streptomyces fodineus TW1S1T (98.69 %) and Streptomyces shenzhennensis 172115T (98.68 %). Strain JA03T has a genome size of 9 092 851 bp with DNA G+C content of 71.28 mol%. The average nucleotide identity (ANI)-blast and ANI-MUMmer values of strain JA03T and related type strains were 79.6–89.2 and 86.7–92.5 %, respectively, and the digital DNA–DNA hybridization values were 27.3–46.4 %. Ethyl acetate extract of JA03T exhibited total phenolic content (33.4±0.6 µg mg−1 gallic acid equivalent), ferric reducing power value (70.8±1.8 µg mg−1 ascorbic acid equivalent) and 1,1-diphenyl-2-picrylhydrazyl radical scavenging activity (IC50=67.0±21.1 µg ml−1). Intracellular reactive oxygen species and NO production in RAW264.7 macrophage cells induced by H2O2 and lipopolysaccharide were inhibited with IC50 of 67.40 and 16.95 µg ml−1, respectively. Based on the taxonomic results, it has been concluded that strain JA03T represents a novel species of the genus Streptomyces for which the name Streptomyces barringtoniae sp. nov., is proposed. The type strain is JA03T (=LMG 32415T=TISTR 2999T).
Three novel actinomycete strains, designated as DR6-1T, DR6-2 and DR6-4, isolated from the roots of Dendrobium heterocarpum Lindl in Thailand were studied using a polyphasic taxonomic approach. The strains grew at 20–37 °C, at pH 5–10 and with 5 % (w/v) NaCl. They contained meso-diaminopimelic acid in the cell-wall peptidoglycan and MK-9(H4) was a major menaquinone. Arabinose and galactose were the major sugars in the cell wall. The predominant cellular fatty acids were iso-C16 : 0 and iso-C15 : 0. The detected polar lipids were diphosphatidylglycerol, hydroxyphosphatidylethanolamine, phosphatidylethanolamine, phosphatidylinositol and phosphatidylglycerol. Strains DR6-1T, DR6-2 and DR6-4 shared 99.9–100 % 16S rRNA gene sequence similarity and were closely related to Amycolatopsis echigonensis JCM 21831T (98.7-98.8%). The approximate genome size of strain DR6-1T was 9.6 Mb with a G+C content of 69.6 mol%. The ANIb and dDDH values between genomic sequences of strain DR6-1T and Amycolatopsis echigonensis JCM21831T, Amycolatopsis rubida JCM 10871T and Amycolatopsis nivea KCTC 39515T were 90.55, 92.25, 92.60%, and 47.20, 52.10 and 52.50%, respectively. Based on the phenotypic, chemotaxonomic and genotypic characteristics, it has been concluded that strains DR6-1T, DR6-2 and DR6-4 represent a novel species of the genus Amycolatopsis for which the name Amycolatopsis dendrobii sp. nov. is proposed. The type strain is DR6-1T (=JCM 33742T=KCTC 49546T=TISTR 2840T).
Astaxanthin is a carotenoid pigment extensively used in various industries. Rhodotorula sp. CP72-2, isolated from Calotropis gigantea, showed potential astaxanthin production. In this study, strain CP72-2 was identified as a putative new species in the genus Rhodotorula based on the 26S rRNA gene sequence (98% identity). It was first used as the microbial source for producing astaxanthin. Strain CP72-2 was screened for its astaxanthin production and was identified and quantified by High-Performance Liquid Chromatography (HPLC), Liquid Chromatography-Mass Spectrometry (LC-MS), and UV-Vis spectrophotometer. After a screening of astaxanthin production, various carbon sources, pH, temperature, and incubation period were evaluated for their effect on the astaxanthin production of strain CP72-2. Among the several experimental factors, the most efficient conditions for astaxanthin production were glucose (50 g/L), pH 4.5, 25 °C, and three days of cultivation. The assembly genome of strain CP72-2 has a total length of 21,358,924 bp and a GC content of 64.90%. The putative candidate astaxanthin biosynthesis-associated genes (i.e., CrtE, CrtYB, CrtI, CrtS, CrtR, CrtW, CrtO, and CrtZ) were found. This research presents the first report on the production and optimization of astaxanthin from strain CP72-2 and its genome analysis, focusing on the biotechnological potential of the astaxanthin producer.
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