scholarly journals A Streptomyces sp. NEAU-HV9: Isolation, Identification, and Potential as a Biocontrol Agent against Ralstonia solanacearum of Tomato Plants

2020 ◽  
Vol 8 (3) ◽  
pp. 351 ◽  
Author(s):  
Ling Ling ◽  
Xiaoyang Han ◽  
Xiao Li ◽  
Xue Zhang ◽  
Han Wang ◽  
...  
Keyword(s):  
Antibacterial Activity ◽  
Ralstonia Solanacearum ◽  
Actinomycin D ◽  
Biological Control Agent ◽  
Sequence Similarity ◽  
Morphological Characteristics ◽  
Rrna Gene ◽  
Tomato Seedling ◽  
Genus Streptomyces ◽  
Tomato Seedlings

Ralstonia solanacearum is an important soil-borne bacterial plant pathogen. In this study, an actinomycete strain named NEAU-HV9 that showed strong antibacterial activity against Ralstonia solanacearum was isolated from soil using an in vitro screening technique. Based on physiological and morphological characteristics and 98.90% of 16S rRNA gene sequence similarity with Streptomyces panaciradicis 1MR-8T, the strain was identified as a member of the genus Streptomyces. Tomato seedling and pot culture experiments showed that after pre-inoculation with the strain NEAU-HV9, the disease occurrence of tomato seedlings was effectively prevented for R. solanacearum. Then, a bioactivity-guided approach was employed to isolate and determine the chemical identity of bioactive constituents with antibacterial activity from strain NEAU-HV9. The structure of the antibacterial metabolite was determined as actinomycin D on the basis of extensive spectroscopic analysis. To our knowledge, this is the first report that actinomycin D has strong antibacterial activity against R. solanacearum with a MIC (minimum inhibitory concentration) of 0.6 mg L−1 (0.48 μmol L−1). The in vivo antibacterial activity experiment showed that actinomycin D possessed significant preventive efficacy against R. solanacearum in tomato seedlings. Thus, strain NEAU-HV9 could be used as BCA (biological control agent) against R. solanacearum, and actinomycin D might be a promising candidate for a new antibacterial agent against R. solanacearum.

scholarly journals Characterization of a Novel Endophytic Actinomycete, Streptomyces physcomitrii sp. nov., and Its Biocontrol Potential Against Ralstonia solanacearum on Tomato

2020 ◽  
Vol 8 (12) ◽  
pp. 2025
Author(s):  
Xiaoxin Zhuang ◽  
Congting Gao ◽  
Chenghui Peng ◽  
Zhiyan Wang ◽  
Junwei Zhao ◽  
...  
Keyword(s):  
Ralstonia Solanacearum ◽  
Sequence Similarity ◽  
Draft Genome ◽  
Morphological Characteristics ◽  
Antagonistic Activity ◽  
Diaminopimelic Acid ◽  
Rrna Gene ◽  
Polar Lipid Profile ◽  
Genus Streptomyces ◽  
Endophytic Actinomycete

Bacterial wilt of tomato is a destructive disease caused by Ralstonia solanacearum throughout the world. An endophytic actinomycete with antagonistic activity, designated strain LD120T, was isolated from moss (Physcomitrium sphaericum (Ludw) Fuernr). The biocontrol test demonstrated that co-inoculation by the isolate and the pathogen gave the greatest biocontrol efficiency of 63.6%. Strain LD120T had morphological characteristics and chemotaxonomic properties identical to those of members of the genus Streptomyces. The diamino acid present in the cell wall was LL-diaminopimelic acid. Arabinose, glucose, rhamnose, and ribose occured in whole cell hydrolysates. The menaquinones detected were MK-9(H4), MK-9(H6), MK-9(H8), and MK-9(H2). The polar lipid profile was found to contain diphosphatidylglycerol, phosphatidylethanolamine, and phosphatidylinositol. The major cellular fatty acids were found to be iso-C16:0, iso-C17:0, anteiso-C15:0, and C16:1 ω7c. The DNA G+C content of the draft genome sequence, consisting of 7.6 Mbp, was 73.1%. Analysis of the 16S rRNA gene sequence showed that strain LD120T belongs to the genus Streptomyces, with the highest sequence similarity to Streptomyces azureus NRRL B-2655T (98.97%), but phylogenetically clustered with Streptomyces anandii NRRL B-3590T (98.62%). Multilocus sequence analysis based on five other house-keeping genes (atpD, gyrB, rpoB, recA, and trpB) and the low level of DNA–DNA relatedness, as well as phenotypic differences, allowed strain LD120T to be differentiated from its closely related strains. Therefore, the strain was concluded to represent a novel species of the genus Streptomyces, for which the name Streptomycesphyscomitrii sp. nov. was proposed. The type strain was LD120T (=CCTCC AA 2018049T = DSM 110638T).

scholarly journals Diversity and antibacterial activity of fungal endophytes from Eucalyptus exserta

2021 ◽  
Vol 21 (1) ◽  
Author(s):  
Ziling Mao ◽  
Weihao Zhang ◽  
Chunyin Wu ◽  
Hao Feng ◽  
Yuanhang Peng ◽  
...  
Keyword(s):  
Antibacterial Activity ◽  
Endophytic Fungi ◽  
Ralstonia Solanacearum ◽  
Large Scale ◽  
Antimicrobial Agents ◽  
Fungal Endophytes ◽  
Morphological Characteristics ◽  
Plant Diseases ◽  
Rrna Gene ◽  
Fungal Isolates

Abstract Background Eucalyptus bacterial wilt caused by Ralstonia solanacearum is an important eucalyptus disease. Endophytic fungi, an important source of natural active substances, provide a new breakthrough for the control of plant diseases. Results In the present study, 80 endophytic fungal isolates were obtained from the healthy branches and fruits of Eucalyptus exserta. Fifteen distinct isolates (MK120854-MK120868) were selected for further taxonomic identification through morphological trait assessments and internal transcribed spacer (ITS) region-rRNA gene sequence analysis. Thirteen genera, namely, Phyllosticta, Penicillium, Eutypella, Purpureocillium, Talaromyces, Lophiostoma, Cladosporium, Pestalotiopsis, Chaetomium, Fusarium, Gongronella, Scedosporium and Pseudallescheria, were identified on the basis of their morphological characteristics. Members of the genus Phyllosticta were the primary isolates, with a colonization frequency (CF) of 27.5 %. Most of the fungal isolates displayed antibacterial activity. The crude extracts obtained from Lophiostoma sp. Eef-7, Pestalotiopsis sp. Eef-9 and Chaetomium sp. Eef-10 exhibited strong inhibition on the test bacteria, and Lophiostoma sp. Eef-7 was further cultured on a large scale. Three known compounds, scorpinone (1), 5-deoxybostrycoidin (2) and 4-methyl-5,6-dihydro-2 H-pyran-2-one (3), were isolated from the endophytic fungus Lophiostoma sp. Eef-7 associated with E. exserta. The structures of these compounds were elucidated by analysis of 1D and 2D NMR and HR-ESI-MS spectra and a comparison of their spectral data with published values. Compounds 1 and 2 showed weak antimicrobial activity against Ralstonia solanacearum. Conclusions Endophytic fungi from Eucalyptus exserta may represent alternative sources of antimicrobial agents. Lophiostoma sp. Eef-7 can produce 2-azaanthraquinone derivatives and shows weak antibacterial activity against Ralstonia solanacearum.

scholarly journals Characterization of Streptomyces sporangiiformans sp. nov., a Novel Soil Actinomycete with Antibacterial Activity against Ralstonia solanacearum

2019 ◽  
Vol 7 (9) ◽  
pp. 360 ◽  
Author(s):  
Junwei Zhao ◽  
Liyuan Han ◽  
Mingying Yu ◽  
Peng Cao ◽  
Dongmei Li ◽  
...  
Keyword(s):  
Antibacterial Activity ◽  
Sequence Analysis ◽  
16S Rrna ◽  
16S Rrna Gene ◽  
Ralstonia Solanacearum ◽  
Diaminopimelic Acid ◽  
Rrna Gene ◽  
Unidentified Phospholipid ◽  
Phytopathogenic Bacterium ◽  
Genus Streptomyces

Ralstonia solanacearum is a major phytopathogenic bacterium that attacks many crops and other plants around the world. In this study, a novel actinomycete, designated strain NEAU-SSA 1T, which exhibited antibacterial activity against Ralstonia solanacearum, was isolated from soil collected from Mount Song and characterized using a polyphasic approach. Morphological and chemotaxonomic characteristics of the strain coincided with those of the genus Streptomyces. The 16S rRNA gene sequence analysis showed that the isolate was most closely related to Streptomyces aureoverticillatus JCM 4347T (97.9%). Phylogenetic analysis based on 16S rRNA gene sequences indicated that the strain formed a cluster with Streptomyces vastus JCM4524T (97.4%), S. cinereus DSM43033T (97.2%), S. xiangluensis NEAU-LA29T (97.1%) and S. flaveus JCM3035T (97.1%). The cell wall contained LL-diaminopimelic acid and the whole-cell hydrolysates were ribose, mannose and galactose. The polar lipids were diphosphatidylglycerol (DPG), phosphatidylethanolamine (PE), hydroxy-phosphatidylethanolamine (OH-PE), phosphatidylinositol (PI), two phosphatidylinositol mannosides (PIMs) and an unidentified phospholipid (PL). The menaquinones were MK-9(H4), MK-9(H6), and MK-9(H8). The major fatty acids were iso-C17:0, C16:0 and C17:1 ω9c. The DNA G+C content was 69.9 mol %. However, multilocus sequence analysis (MLSA) based on five other house-keeping genes (atpD, gyrB, recA, rpoB, and trpB), DNA–DNA relatedness, and physiological and biochemical data showed that the strain could be distinguished from its closest relatives. Therefore, it is proposed that strain NEAU-SSA 1T should be classified as representatives of a novel species of the genus Streptomyces, for which the name Streptomyces sporangiiformans sp. nov. is proposed. The type strain is NEAU-SSA 1T (=CCTCC AA 2017028T = DSM 105692T).

scholarly journals Taxonomic Characterization, and Secondary Metabolite Analysis of Streptomyces triticiradicis sp. nov.: A Novel Actinomycete with Antifungal Activity

2020 ◽  
Vol 8 (1) ◽  
pp. 77 ◽  
Author(s):  
Zhiyin Yu ◽  
Chuanyu Han ◽  
Bing Yu ◽  
Junwei Zhao ◽  
Yijun Yan ◽  
...  
Keyword(s):  
Antifungal Activity ◽  
16S Rrna ◽  
Sequence Similarity ◽  
Triticum Aestivum L ◽  
Biosynthetic Gene Cluster ◽  
Rrna Gene ◽  
Phenotypic Properties ◽  
Genus Streptomyces ◽  
Antagonistic Microorganisms ◽  
Taxonomic Characterization

The rhizosphere, an important battleground between beneficial microbes and pathogens, is usually considered to be a good source for isolation of antagonistic microorganisms. In this study, a novel actinobacteria with broad-spectrum antifungal activity, designated strain NEAU-H2T, was isolated from the rhizosphere soil of wheat (Triticum aestivum L.). 16S rRNA gene sequence similarity studies showed that strain NEAU-H2T belonged to the genus Streptomyces, with high sequence similarities to Streptomyces rhizosphaerihabitans NBRC 109807T (98.8%), Streptomyces populi A249T (98.6%), and Streptomyces siamensis NBRC 108799T (98.6%). Phylogenetic analysis based on 16S rRNA, atpD, gyrB, recA, rpoB, and trpB gene sequences showed that the strain formed a stable clade with S. populi A249T. Morphological and chemotaxonomic characteristics of the strain coincided with members of the genus Streptomyces. A combination of DNA–DNA hybridization results and phenotypic properties indicated that the strain could be distinguished from the abovementioned strains. Thus, strain NEAU-H2T belongs to a novel species in the genus Streptomyces, for which the name Streptomyces triticiradicis sp. nov. is proposed. In addition, the metabolites isolated from cultures of strain NEAU-H2T were characterized by nuclear magnetic resonance (NMR) and mass spectrometry (MS) analyses. One new compound and three known congeners were isolated. Further, genome analysis revealed that the strain harbored diverse biosynthetic potential, and one cluster showing 63% similarity to natamycin biosynthetic gene cluster may contribute to the antifungal activity. The type strain is NEAU-H2T (= CCTCC AA 2018031T = DSM 109825T).

scholarly journals Taxonomic Characterization and Secondary Metabolite Analysis of NEAU-wh3-1: An Embleya Strain with Antitumor and Antibacterial Activity

2020 ◽  
Vol 8 (3) ◽  
pp. 441 ◽  
Author(s):  
Han Wang ◽  
Tianyu Sun ◽  
Wenshuai Song ◽  
Xiaowei Guo ◽  
Peng Cao ◽  
...  
Keyword(s):  
Antibacterial Activity ◽  
Pathogenic Bacteria ◽  
Fermentation Broth ◽  
Sequence Similarity ◽  
Tumor Cell Line ◽  
Triticum Aestivum L ◽  
New Drugs ◽  
Rrna Gene ◽  
Physiological Characterization ◽  
Ic50 Values

Cancer is a serious threat to human health. With the increasing resistance to known drugs, it is still urgent to find new drugs or pro-drugs with anti-tumor effects. Natural products produced by microorganisms have played an important role in the history of drug discovery, particularly in the anticancer and anti-infective areas. The plant rhizosphere ecosystem is a rich resource for the discovery of actinomycetes with potential applications in pharmaceutical science, especially Streptomyces. We screened Streptomyces-like strains from the rhizosphere soil of wheat (Triticum aestivum L.) in Hebei province, China, and thirty-nine strains were obtained. Among them, the extracts of 14 isolates inhibited the growth of colon tumor cell line HCT-116. Strain NEAU-wh-3-1 exhibited better inhibitory activity, and its active ingredients were further studied. Then, 16S rRNA gene sequence similarity studies showed that strain NEAU-wh3-1 with high sequence similarities to Embleya scabrispora DSM 41855T (99.65%), Embleya hyalina MB891-A1T (99.45%), and Streptomyces lasii 5H-CA11T (98.62%). Moreover, multilocus sequence analysis based on the five other house-keeping genes (atpD, gyrB, rpoB, recA, and trpB) and polyphasic taxonomic approach comprising chemotaxonomic, phylogenetic, morphological, and physiological characterization indicated that the isolate should be assigned to the genus Embleya and was different from its closely related strains, therefore, it is proposed that strain NEAU-wh3-1 may be classified as representatives of a novel species of the genus Embleya. Furthermore, active substances in the fermentation broth of strain NEAU-wh-3-1 were isolated by bioassay-guided analysis and identified by nuclear magnetic resonance (NMR) and mass spectrometry (MS) analyses. Consequently, one new Zincophorin analogue together with seven known compounds was detected. The new compound showed highest antitumor activity against three human cell lines with the 50% inhibition (IC50) values of 8.8–11.6 μg/mL and good antibacterial activity against four pathogenic bacteria, the other known compounds also exhibit certain biological activity.

scholarly journals Genome-based analyses reveal the presence of 12 heterotypic synonyms in the genus Streptomyces and emended descriptions of Streptomyces bottropensis, Streptomyces celluloflavus, Streptomyces fulvissimus, Streptomyces glaucescens, Streptomyces murinus, and Streptomyces variegatus

2020 ◽  
Vol 70 (6) ◽  
pp. 3924-3929 ◽  
Author(s):  
Munusamy Madhaiyan ◽  
Venkatakrishnan Sivaraj Saravanan ◽  
Wah-Seng See-Too
Keyword(s):  
Type Species ◽  
Sequence Similarity ◽  
Orthologous Gene ◽  
Gene Clusters ◽  
Amino Acid Identity ◽  
Rrna Gene ◽  
Genus Streptomyces ◽  
Content Type ◽  
Link Type ◽  
Streptomyces Glaucescens

Phylogenetic analysis based on 16S rRNA gene sequences of the genus Streptomyces showed the presence of six distinguishable clusters, with 100 % sequence similarity values among strains in each cluster; thus they shared almost the same evolutionary distance. This result corroborated well with the outcome of core gene (orthologous gene clusters) based genome phylogeny analysis of 190 genomes including the Streptomyces species in those six clusters. These preeminent results led to an investigation of genome-based indices such as digital DNA–DNA hybridization (dDDH), average nucleotide identity (ANI) and average amino acid identity (AAI) for the strains in those six clusters. Certain strains recorded genomic indices well above the threshold values (70 %, 95–96 % and >95 % for dDDH, ANI and AAI, respectively) determined for species affiliation, suggesting only one type strain belongs to described species and the other(s) may need to be reduced in taxa to a later heterotypic synonym. To conclude, the results of comprehensive analyses based on phylogenetic and genomic indices suggest that the following six reclassifications are proposed: Streptomyces flavovariabilis as a later heterotypic synonym of Streptomyces variegatus ; Streptomyces griseofuscus as a later heterotypic synonym of Streptomyces murinus ; Streptomyces kasugaensis as a later heterotypic synonym of Streptomyces celluloflavus ; Streptomyces luridiscabiei as a later heterotypic synonym of Streptomyces fulvissimus ; Streptomyces pharetrae as a later heterotypic synonym of Streptomyces glaucescens ; and Streptomyces stelliscabiei as a later heterotypic synonym of Streptomyces bottropensis .

scholarly journals Sponge-Associated Actinobacteria: Morphological Character and Antibacterial Activity against Pathogenic Bacteria

2017 ◽  
Vol 3 (1) ◽  
pp. 21-26
Author(s):  
SASMIATI FARACH DITA ◽  
SRI BUDIARTI ◽  
YULIN LESTARI
Keyword(s):  
Antimicrobial Activity ◽  
Antibacterial Activity ◽  
Pathogenic Bacteria ◽  
Marine Ecosystem ◽  
Morphological Characteristics ◽  
Antibacterial Activities ◽  
Morphological Characters ◽  
Antimicrobial Activities ◽  
Shigella Dysenteriae ◽  
Rrna Gene

Sponge-associated actinobacteria may diverse and have potency to produce bioactive compounds. Diversity and antimicrobial activity of indigenous sponge-associated actinobacteria isolated from the marine ecosystem in Indonesia have not much been explored. This work aimed to assess morphological and antibacterial activity of sponge-associated actinobacteria. The morphological characteristics were examined based on their color of aerial and substrate mycelia, and pigmentation, while antibacterial activities were assayed using the antagonist technique. The selected actinobacterial isolate was identified using 16S rRNA gene. Various sponge-associated actinobacteria were successfully isolated from Hyrtios sp., Callyspongia sp., and Neofibularia sp. sponges. A total of 62 actinobacterial isolates were obtained, and each isolate showed a variety of morphological characters, which could be seen in aerial mass color, substrate mass color, and pigmentation. Actinobacterial isolates were tested against human pathogenic bacteria, i.e. Staphylococcus aureus and Methicillin-Resistant S. aureus, representing Gram-positive, and Escherichia coli EPEC K1-1 and Shigella dysenteriae, representing Gram-negative. Most of actinobacterial isolates had antimicrobial activities at least against one of pathogenic bacteria. High activity was shown by NOHa.2, isolated from Neofibularia, and HRHa.5 isolated from Hyrtios. The NOHa.2 showed the highest antimicrobial activity against S. dysenteriae, meanwhile, HRHa.5 showed antimicrobial activity against 3 of 4 tested bacterial pathogens. These data showed diversity of sponge-asccociated actinobacteria from marine ecosystem in Indonesia, and several of them have potency as source of antibacterial compounds

scholarly journals Antagonistic Potential of Soil Streptomyces Isolates from Southern Thailand to Inhibit Foodborne Bacterial Pathogens

2021 ◽  
Vol 2021 ◽  
pp. 1-9
Author(s):  
Waenurama Chemoh ◽  
Wahida Bin-Ismail ◽  
Sawitree Dueramae
Keyword(s):  
Antibacterial Activity ◽  
Pathogenic Bacteria ◽  
Bacterial Pathogens ◽  
Antagonistic Activity ◽  
Rrna Gene ◽  
Rice Soils ◽  
Streptomyces Species ◽  
Genus Streptomyces ◽  
Crude Extracts ◽  
Broth Microdilution Method

Streptomyces are well known for their competence to produce thousands of bioactive secondary metabolites and enzymes. This study aimed to assess the inhibitory activities of crude extracts from diverse Streptomyces collected from rice soils in Narathiwat, Thailand, against foodborne bacterial pathogens. In total, 136 Actinomycete isolates were screened using a cross-streak method for the ability to produce effective metabolites against 5 pathogenic bacteria. Out of these, 19 (13.97%) isolates had antibacterial activity against at least one tested bacterium. Most of the isolates could strongly suppress the growth of S. aureus ATCC25923 and B. cereus MTCC430 except P. aeruginosa ATCC27853. On the basis of morphological, cultural, and biochemical characteristics, all potent isolates exhibited typical features that fitted the genus Streptomyces. Two of the 7 selected ethyl acetate crude extracts had good antagonistic activity against S. aureus ATCC25923 and B. cereus MTCC430 when tested using the agar well diffusion assay. Furthermore, minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values of the 2 extracts evaluated using the colorimetric broth microdilution method ranged from 256 to >1,024 μg/ml against the tested bacteria. The partial nucleotide sequences of the 16S rRNA gene led to identifying both active isolates as Streptomyces species. These active Streptomyces isolates could provide an interesting source for generating innumerable natural compounds with antibacterial activity that can presumably be developed to fight bacterial pathogens in the near future.

Potential antibiotic production of Streptomyces justiciae sp. nov., isolated from the root of Justicia subcoriacea

2021 ◽  
Vol 71 (9) ◽  
Author(s):  
Wongsakorn Phongsopitanun ◽  
Pawina Kanchanasin ◽  
Paranee Sripreechasak ◽  
Kanokorn Rueangsawang ◽  
Anan Athipornchai ◽  
...  
Keyword(s):  
Type Strain ◽  
Type Species ◽  
Actinomycin D ◽  
Antibiotic Production ◽  
Morphological Characteristics ◽  
Diaminopimelic Acid ◽  
Rrna Gene ◽  
Content Type ◽  
Link Type ◽  
Gene Similarity

Endophytic actinobacterial strain 3R004T was isolated from a root of Justicia subcoriacea collected in Thailand. In this report, the taxonomic position of this strain is described using a polyphasic approach. Based on the morphological characteristics and chemical composition of its cells, strain 3R004T was identified as a member of the genus Streptomyces . It produced a long chain of cylindrical spores on aerial mycelia. ll-Diaminopimelic acid was detected in the cell wall peptidoglycan. The menaquinones were MK-9(H4), MK-9(H6) and MK-9(H8). C16 : 0, iso-C16 : 0, anteiso-C15 : 0 and iso-C15 : 0 were detected as the major cellular fatty acids. Polar lipids were diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, phosphatidylinositol and one unidentified lipid. Strain 3R004T showed the highest 16S rRNA gene similarity of 99.45 % to Streptomyces cyaneochromogenes MK-45T. The phylogenomic results indicated that strain 3R004T was close to Streptomyces aquilus GGCR-6T and Streptomyces antibioticus DSM 40234T. The DNA–DNA hybridization and average nucleotide identity values among strain 3R004T and closely related Streptomyces species were 35.5–63.1 % and 82.7–94.3 %, respectively. The type strain produced actinomycin D antibiotic as the major secondary metabolite. The maximum productivity of the actinomycin D (378 mg l−1) was observed when the strain was grown in 301 broth at 30 °C, 180 r.p.m. for 12 days. On the basis of phenotypic and genotypic evidence, strain 3R004T represents a novel species of the genus Streptomyces , for which the name Streptomyces justiciae is proposed. The type strain is 3R004T (=LMG 32138T=TBRC 13128T=NBRC 115065T).

Melanogenic actinomycetes from rhizosphere soil — antagonistic activity against Xanthomonas oryzae and plant-growth-promoting traits

2015 ◽  
Vol 61 (2) ◽  
pp. 164-170 ◽  
Author(s):  
Supattra Muangham ◽  
Wasu Pathom-aree ◽  
Kannika Duangmal
Keyword(s):  
Morphological Characteristics ◽  
Antagonistic Activity ◽  
Xanthomonas Oryzae ◽  
Diaminopimelic Acid ◽  
Rrna Gene ◽  
Genus Streptomyces ◽  
Gene Sequence Analysis ◽  
Plant Growth Promoting ◽  
Growth Promoting ◽  
The 16S Rrna Gene

A total of 210 melanogenic actinomycetes were isolated from 75 rhizospheric soils using ISP6 and ISP7 agar supplemented with antifungal and antibacterial agents. Their morphological characteristics and the presence of ll-diaminopimelic acid in whole-cell hydrolyzates revealed that all isolates belonged to the genus Streptomyces. Their ability to inhibit the growth of 2 pathogenic rice bacteria, Xanthomonas oryzae pv. oryzae and Xanthomonas oryzae pv. oryzicola, was observed using the agar overlay method. The results indicated that 61.9% of the isolates could inhibit at least one of the tested rice pathogens. Among these, isolate TY68-3 showed the highest antibacterial activity and siderophore production. The 16S rRNA gene sequence analysis of 46 representative isolates revealed that isolates with high similarity to Streptomyces bungoensis were frequently found. The present study indicated the potential of melanogenic actinomycetes for use as biocontrol agents against X. oryzae as well as their diversity in rhizospheric soils.

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