Isolation And Identification Of Myxobacteria From Ordos Plateau Area And Preliminary Analysis Of Their Antibiotic Activities Against Phytophthora Infestans

Myxobacteria are a group of gram-negative and rod-shaped eubacteria with complex multicellular behavior and morphology.They have sophisticated intercellular communication systems.Under starvation conditions,they can produce fruiting bodies,in which the vegetative cells can convert into myxospores.Myxobacteria can produce a wealth of bioactive secondary metabolites.Therefore,they have a great value for the research and development of anti-tumor,anti-fungal,anti-viral and anti-bacterial drugs.The main purpose of this study is to develop new myxobacterium resources and obtain the strains and secondary metabolites with high activities against potato late blight pathogen.In this study,46 soil samples from Erdos and Wuhai areas in western Inner Mongolia Autonomous Region were collected according to the types of soils.The quantity of soil microbe as well as soil physical and chemical properties was determined.Myxobacteria were isolated from these samples and identified.The activities of the purified strains against Phytophthora infestans were analyzed and the fermentation conditions of those strains with high activities were optimized.The number of microorganisms in Erdos and Wuhai areas in western Inner Mongolia is low.The soil pH value is neutral to alkaline.The vast majority of soil is drought and soil fertilizer content is also generally low.191 strains of myxobacteria were isolated from 46 soil samples and 102 of them were purified.The strains belong to 5 genera,11 species.including Myxococcus fulvus,Myxococcus xanthus,Myxococcus virescens.Myxococcus stipitatus,Corallococcus coralloides,Corallococcus macrosporus,Corallococcus exiguous,Pyxicoccus fallax.Cystobacter Violaceus.Cystobacter fuscus,and Archangium gephyra.The number of myxobacteria is gradually declined according to woodland,grassland,cultivated land,and wasteland.The total number of myxobacteria and the number of cellulolytic myxobacteria and bacteriolytic myxobacteria showed a significant correlation with soil available potassium and organic matter and the correlation coefficients with organic matter were 0.690.0.543 and 0.732 respectively.72%of the tested strains had an activity against Phytophthora infestans and especially the strain E10,E11,and E12 exhibited the strangest antagonistic activity among these strains,and their inhibition zone diameters reached to 26,24 and 24 mm respectively.By further identification,it was indicated that the strain E10,Ell,and E12 was respectively identified as Corallococcus exiguous,Pyxicoccus fallax,and Corallococcus coralloides.The optimal fermentation medium for the strain E10 and E12 was the MX04 medium(MD1).The optimum fermentation conditions were as follows:fermentation temperature 32 ℃,fermentation time 11 days,and salinity 0%.The optimum fermentation medium for the strain El 1 was the MXO1 medium(VY/2).The optimum fermentation conditions were as follows:fermentation temperature 36 ℃,time 11 d,salinity 0.5%.The bioactive substances in the fermentation broth of the 3 strains against Phytophthora infestans were easily dissolved in organic matter but difficultly dissolved in water.The secondary metabolites produced by the strains in the fermentation process could be adsorbed by macroporous resin.The completion of this work has provided the basic date for the development of biological pesticides against Phytophthora infestans.