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Community Structures and Antifungal Activity of Root-Associated Endophytic Actinobacteria in Healthy and Diseased Cucumber Plants and Streptomyces sp. HAAG3-15 as a Promising Biocontrol Agent.

ABSTRACT: Microorganisms related to plant roots are vital for plant growth and health and considered to be the second genome of the plant. When the plant is attacked by plant pathogens, the diversity and community structure of plant-associated microbes might be changed. The goal of this study is to characterize differences in root-associated endophytic actinobacterial community composition and antifungal activity between Fusarium wilt diseased and healthy cucumber and screen actinobacteria for potential biological control of Fusarium wilt of cucumber. In the present research, three healthy plants (also termed "islands") and three obviously diseased plants (naturally infected by F. oxysporum f. sp. cucumerinum) nearby the islands collected from the cucumber continuous cropping greenhouse were chosen as samples. Results of culture-independent and culture-dependent analysis demonstrated that actinomycetes in the healthy roots were significantly more abundant than those of diseased roots. Moreover, there were seven strains with antifungal activity against F. oxysporum f. sp. cucumerinum in healthy cucumber roots, but only one strain in diseased cucumber roots. Out of these eight strains, the isolate HAAG3-15 was found to be best as it had the strongest antifungal activity against F. oxysporum f. sp. cucumerinum, and also exhibited broad-spectrum antifungal activity. Thus, strain HAAG3-15 was selected for studying its biocontrol efficacy under greenhouse conditions. The results suggested that the disease incidence and disease severity indices of cucumber Fusarium wilt greatly decreased (p < 0.05) while the height and shoot fresh weight of cucumber significantly increased (p < 0.05) after inoculating strain HAAG3-15. On the basis of morphological characteristics, physiological and biochemical properties and 100% 16S ribosomal RNA (rRNA) gene sequence similarity with Streptomyces sporoclivatus NBRC 100767T, the isolate was assigned to the genus Streptomyces. Moreover, azalomycin B was isolated and identified as the bioactive compound of strain HAAG3-15 based on analysis of spectra using a bioactivity-guided method. The stronger antifungal activity against F. oxysporum f. sp. cucumerinum, the obvious effect on disease prevention and growth promotion on cucumber seedlings in the greenhouse assay, and the excellent broad-spectrum antifungal activities suggest that strain HAAG3-15 could be developed as a potential biocontrol agent against F. oxysporum f. sp. cucumerinum used in organic agriculture. These results suggested that the healthy root nearby the infected plant is a good source for isolating biocontrol and plant growth-promoting endophytes.

SUBMITTER: Cao P

PROVIDER: S-EPMC7074843 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BackgroundNewcastle disease virus (NDV) is a severe disease that affects domestic and wild birds. Controlled antibiotics derived from probiotics have been examined as prospective solutions for preserving seroconversion in NDV-vaccinated fowl. In this study, the secondary metabolite "telomycin" was extracted from Streptomyces coeruleorubidus (S. coeruleorubidus) isolated from Egypt's cultivated soil. The structure of telomycin was determined by the elucidation of spectroscopic analysis, including nuclear magnetic resonance (NMR) and mass spectrometry (MS) spectra, and comparison with the literature. The antiviral activity of the secondary metabolite was tested by checking its effect on NDV hemagglutination activity (HA). Moreover, HA of NDV was tested after inoculation of NDV (control) and a combination of telomycin and NDV in 10- days- specific pathogen-free embryonated chicken eggs (SPF-ECE) daily candling. Histopathological examination was performed for chorioallantoic membranes and liver of SPF-ECE.ResultsS. coeruleorubidus secondary metabolite "telomycin" showed complete hemagglutination inhibition (HI) activity of NDV strain (MN635617) with log106 infectivity titers (EID50/mL). The HA of NDV strain was 8 log2 and 9 log2 with 0.5% and 0.75% of chicken RBCs, respectively. Preserved structures of chorioallantoic-membranes (CAM) with dilated capillary networks were observed in the treated group inoculated with telomycin and NDV. Histological changes in SPF-ECE liver were examined after inoculation in ova to further characterize the telomycin effect. Telomycin and NDV mixture inoculated group showed preserved cytoarchitecture of hepatocytes with the presence of perivascular foci of lymphocytes. The group that was inoculated with telomycin alone showed normal histology of hepatic acini, central veins, and portal triads.ConclusionS. coeruleorubidus telomycin is a promising bioactive agent that might be a biological weapon against a deadly chicken NDV that costs farmers a lot of money.

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Community Structures and Antifungal Activity of Root-Associated Endophytic Actinobacteria in Healthy and Diseased Cucumber Plants and Streptomyces sp. HAAG3-15 as a Promising Biocontrol Agent.

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