Identification and secondary metabolites of strain B25-I-3 against Phytophthora infestans

Abstract:

[Background] Myxobacteria are a group of higher prokaryotes with social behaviors. They can produce rich, diverse, and novel secondary metabolites with biological activity, and have great research and development value. [Objective] To screen and identify culturable myxobacteria resistant to the pathogen of potato late blight from soil samples and study secondary metabolites of the isolates. [Methods] Myxobacteria were isolated from soil samples by rabbit feces inducing method. The strain resistant to the pathogen of potato late blight was identified by morphological observation and the 16S rRNA gene sequence analysis. Then, the fermentation parameters were studied by the combination of univariate analysis and orthogonal optimization. The stability and antibacterial activity of the active substances in the concentrated fermentation broth were detected by the filter paper method. The active substances were separated by TLC and HPLC, and the components with antibiotic activity were detected by HPLC-MS. The anti-disease effect of the active substances on potato late blight was determined by the in vitro leaf method. [Results] Strain B25-I-3 isolated from the soil sample showed strong antagonistic activity against P. infestans and was identified as Myxococcus fulvus. The antibiotic substances against P. infestans were mainly present in the extracellular matrix. Its optimal fermentation conditions were: shaking speed 180 r/min, inoculum size 10%, incubation temperature 30 °C, incubation time 7 d. The active substances produced by strain B25-I-3 were highly tolerant to the treatment of protease K, ultraviolet and natural light, temperature, and were easily preserved at low temperatures. The antibacterial and antifungal activity analysis showed the active substances exhibited different degrees of antagonism against Bacillus subtilis, Staphylococcus aureus, Escherichia coli, Saccharomyces cerevisiae, Rhizoctonia solani, Fusarium oxysporum, Sclerotinia sclerotiorum. The antagonistic components of strain B25-I-3 contained N-(3-amino-2-hydroxypropyl)-N-methylsulfuric diamide and methyl(2R)-2-azido-3-hydroxyl-2-methylpropanoate. The results of disease control on potato leaves showed that the active substances could significantly inhibit the infection of P. infestans on the detached potato leaves of different varieties without harming. [Conclusion] This study provides basic data for the isolation and identification of active substances and the development of biopesticide against potato late blight.