Identification, Optimization of fermentation process of an antagonistic actinomycete S5-1 and evaluation of antibacterial activity of the fermented crude extract

Abstract:

[Background] How to effectively prevent and control plant diseases and achieve safe crop production without causing damage to the agro-environment is a key problem to be solved in the sustainable development of agriculture. [Objective] The strains and active metabolites of Streptomyces strains were screened out to provide the strain resources and approaches for the biocontrol of plant diseases, which is of great practical significance for the research on the potential application of strain S5-1 in the biocontrol of plant diseases. [Methods] The antimicrobial activity was examined by the plate confrontation method and the plate culture method with the fermentation broth of the strain. The strain was identified based on the morphological and physicochemical characteristics and 16S rRNA gene sequences. Furthermore, the single factor and orthogonal experiments were carried out to optimize the fermentation conditions, and the antimicrobial activity of the fermented crude extract was examined. [Results] The strain S5-1 had strong inhibitory activities on ten plant pathogens and was identified as Streptomyces toxytricini. The fermentations conditions were optimized as follows: TSB medium, initial pH 6.5, medium loading capacity of 100 mL/250 mL, inoculation amount of 10%, and fermentation at 28 ℃ for 7 d. The fermented crude extract inhibited the mycelial growth and spore germination of Phytophthora parasitica and Botrytis cinerea. Furthermore, it reduced the infection of the two pathogens in tobacco leaves and cherry tomatoes. The extract was stable at pH 6.0–7.0 and lost activity at the temperature above 37 ℃. In addition, the storage at ‒20 ℃ for 30 d and ultraviolet irradiation not exceeding 6 h caused slight changes in the extract activity. [Conclusion] The development and utilization of strain S5-1 contribute to the green prevention and control of plant diseases and provide excellent strain resources of actinomycetes for biocontrol. This study provide an experimental basis for the research and application of new antimicrobial agents.