Study On Antibacterial Activity Of The Metabolites Of Streptomyces Longissimus SL01 And Cantharidin Derivatives

Biological pesticide is an important part of modern pesticides, which is mainly including three categories- the source of animals, plants and microorganisms. Actinomycetes is an important part of antibiotics. Streptomyces longissimus SL01 showed significant antibacterial activity against fungal pathogens in the dish experiment. Cantharidin is a sesquiterpene compound in Spanish fly which showed high anticancer activity. Norcantharidin is a kind of Cantharidin derivatives which has similar biological activity with Cantharidin while with lower toxicity. The metabolic products of Streptomyces longissimus SL01 and cantharidin derivatives were used as experimental material to study their antimicrobial activities. The main experimental results were as follows:1. Metabolites of the strain SL01 The bacterial and fungal inhibition activity of the fermented broth of the strain SL01 was preliminarily evaluated by means of the dish inhibition test. It showed significant antibacterial activity to the plant pathogenic fungi. Through rapid identification of secretions test, the strain SL01 could secrete degradation enzymes, including protease, amylase, lipase and cellulose. The thermal and p H stability of the antibacterial substances of strain SL01 was detected. When the temperature was 40℃, the bacteriostatic activity of fermentation broth was not affected, but when the temperature raised to 60℃, the bacteriostatic activity decreased significantly. The fermentation broth of the strain SL01 was stable to different p H. When p H=6, the antibacterial activity of fermentation broth was higher than CK. When p H was between 4 to 10, the antibacterial activity unchanged, only when p H=2 and 12, the antibacterial activity decreased significantly.2. Separation and antimicrobial activity of metabolites from the strain SL01 The fermentation broth of the strain SL01 was processed by macroporous adsorption resin chromatography, silica gel column chromatography, gel column chromatography and high performance liquid chromatography. The Component 2 had significant antibacterial activity. The EC50 on Sclerotinia sclerotiorum was 16.7115 μg/m L. The EC50 on Valsa mali and Alternaria alternata were 40.1414 μg/m L and 50.0402μg/m L respectively. The EC50 on spore germination of Botrytis cinerea was 34.6153 μg/m L.3. Antimicrobial effect of cantharidin derivatives The Cantharidin derivatives showed inhibition effect to the tested 5 plant pathogenic fungi. The EC50 of Cantharidin derivatives BY-18, BY-30 and BY-31 on S. sclerotiorum were 38.226μg/m L, 41.4973μg/m L and 43.2631μg/m L, respectively; The EC50 of Cantharidin derivatives BY-15, BY-18, BY-30 and BY-31 on B. cinerea were 31.8705 μg/m L, 46.3293 μg/m L, 35.3873 μg/m L and 42.2416 μg/m L, respectively; The EC50 of Cantharidin derivatives BY-15 on Cochliobolus sativus was 49.8598 μg/m L.4.The control efficacy of Cantharidin derivatives on S. sclerotiorum Eight Cantharidin derivatives with higher antibacterial activity were selected for the leaf test in vitro. In the group that the derivatives was sprayed on the leaves 24 h prior to the inoculation of fungal, the effect of BY-18 was the best, reaching 70.4%; in the group that the derivatives was sprayed 24 h after the inoculation, the effect of 7-0 was the best, reaching 62.9%.