Mechanism And Preliminary Isolation Of The Active Components Of The Myxobacterial Strain E10 And E12 Against Potato Late Blight Pathogen

Myxobacteria belong to gram-negative bacteria,which are a group of higher bacteria between prokaryotes and eukaryotes.Recent studies have showed that most of secondary metabolites of myxobacteria have the antifungal and antibacterial activity.With the development and utilization of myxobacteria and their secondary metabolites,myxobacteria have become a "small factory" for discovering natural products.Therefore,myxobacteria have great development potential and practical value.The myxobacterial strain E10 and E12,which were isolated from previous work in our laboratory,belonged to Corallococcus exiguous and Corallococcus coralloides.It was found that the secondary metabolites produced by the two strains had high antibiotic activity against potato late blight pathogen,which might have potential application value in the prevention and treatment of potato late blight.The main purpose of this paper is to study the stability and mechanism of the secondary metabolites of the two strains against potato late blight pathogen,and detect the prevention and treatment roles of their active substances on the detached potato leaves infected by P.infestans,and explore the seperation conditions of the active substances preliminarily,which may have some contribution to the research and development of pesticide originated from myxobacteria against potato late blight in the future.The results showed that the optimal temperature of the secondary metabolites of the strain E10 and E12 was room temperature,but their activity could be maintained relatively at high or low temperature.The optimum pH value of the active substances of the two strains was 7,but their activity could be maintained relatively under acidic or alkaline conditions.There was no significant change in the activity of secondary metabolites of two strains under natural light,ultraviolet light and protease K treatment.All of these results suggested that the secondary metabolites of the strain E10 and E12 had better stability of temperature,pH,UV light,natural light,and protease K.The secondary metabolites of the strain E10 were more appropriate to be stored at 4 ? and room temperature and the secondary metabolites of the strain E12 were more appropriate to be stored at 4 ?for a short time,while the secondary metabolites of the two strains were more appropriate to be stored at-80 ?.The secondary metabolites of the two strains could inhibit the mycelial growth and development and reduce the number of sporangia and zoospores.The active substances could also reduced the number of oospores produced in the sexual reproduction of P.infestans and affected the development of the oospores.Furthermore,the active substances could increase the permeability of cell membrane and enhance the lipid peroxidation of membrane of the mycelia,while the substances had no significant influence on the content of ergosterol and soluble protein of the hyphae,suggesting that the active substances of the two strains could reduce the infection of P.infestans by inhibit the mycelial growth and development,asexual and sexual reproduction of the pathogen.In addition,the substances may also play a role by enhancing the permeability of cell membrane because of the increasing of the lipid peroxidation and damage of the cell membrane.High concentration of secondary metabolites of the strain E10 and E12 had better prevention and treatment effects on the detached potato leaves infected by P.infestans.The separation effects of secondary metabolites of the strain E10 and E12 were good with methanol and water as mobile phase.Most of the active ingredients against P.infestans could be dissolved by acetone and methanol.