Antifungal activity of endophytic Streptomyces strains from Dendrobium orchids and the secondary metabolites of strain DR7-3 with its genome analysis

Abstract

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.

Biocontrol of Cercospora Leaf Spot Disease and Enhancement of Defense Response in Vigna radiata (L.) R. Wilczek (Mung Bean) Plants Using Bioformulation of Endophytic Streptomyces sp

“…MR14 significantly inhibited the fungal pathogens F. oxysporum, P. oryzae , and F. moniliforme . In another report, four endophytic Streptomyces species showed antifungal potential against fungal phytopathogens like C. gloeosporiodes , F. oxysporum , F. solani , A. alternaria, and C. oryzae . The antifungal potential of microbes associated with the secondary metabolites (antifungal) shows synergetic effects on the mycelia of the growing fungal pathogens.…”

“…33 In another report, four endophytic Streptomyces species showed antifungal potential against fungal phytopathogens like C. gloeosporiodes, F. oxysporum, F. solani, A. alternaria, and C. oryzae. 34 The antifungal potential of microbes associated with the secondary metabolites (antifungal) shows synergetic effects on the mycelia of the growing fungal pathogens. These antifungal metabolites can cause diverse effects on mycelia like destruction of mycelial morphology, loss of cytoplasm, and aplanations by diffusing into the media.…”

Antagonistic Activity of Endophytic Fungi Isolated From Aloe Vera Leaves Against Some Plant Pathogenic Fungi

“…Endophytic fungi prevent damages to plants by their ability to release enzymes, antibiotics, hydrogen cyanide, and volatile compounds that inhibit pathogen's activities and induce systemic resistance (42). Global trends are shifting towards reducing the use of chemical pesticides due to their severe negative impacts on human health and surrounding ecosystems, with biological control methods are being used to control diseases (39,50). Biocontrol agents (BCAs) are usually fungal or bacterial strains isolated from the plant's phyllosphere, endosphere, or rhizosphere, and they play an important role in controlling plant pathogens (43).…”

“…Antagonism is a phenomenon in which antagonistic organisms suppress or interfere with the normal growth, development, and activity of plant pathogens in their vicinity (20). Antagonism can manifest itself in several mechanisms of biological control of disease, including antibiosis (a metabolite or antibiotic that is inhibited by the antagonist is produced), mycoparasitism (in which the antagonist obtains some or all of its nutrients from the fungal host), induced resistance (induction of plant defense response against plant pathogens), and promotion of plant growth while reducing disease effects, as well as through microbial hormones such as indole acetic acid and gibberellic acid (50). Pseudomonas fluorescens and Azotobacter chroococcum bacteria were used to induce systemic resistance in the barley plant against barley yellow dwarf virus (1).…”