Isolation And Identification Of Myxobacteria In Alashan Area And Preliminary Study On Their Antibiotic Activity Against Phytophthora Infestans

Myxobacteria is a group of gram-negative and gliding bacteria,with a variety of multicellular behaviors and complex morphogenesis.In recent years,myxobacteria have attracted much attention as a source of microorganisms that can produce a variety of secondary metabolites.In this study,38 soil samples were collected from Alashan area and physical and chemical indicators of these soil samples were tested.Soil in Alashan area was in a state of drought and soil p H value was in a neutral to slightly alkaline state.Organic matter and hydrolyzed nitrogen of the soil samples were deficient,while available potassium and phosphorus were relatively rich or appropriate.118 myxobacterial strains were isolated from the 38 soil samples by rabbit dung pellets inducing method,Escherichia coli inducing method and filter paper inducing method and90 strains were purified by directly picking fruiting bodies combined antibiotic treatment.The strains belonged to 6 genera and 11 species of myxobacteria,including Myxococcus fulvus,Myxococcus xanthus,Myxococcus virescens,Myxococcus stipitatus,Myxococcus macrosporus,Corallococcus macrosporus,Pyxidicoccus fallax,Angiococcus disciformi,Cystobacter violaceus,Cystobacter minus,and Archangium gephyra.Myxococcus was the dominant genus in this area.There was a significant positive correlation between culturable myxobacterium resources and soil p H value in this area.The resource of myxobacteria was the most abundant in Meadow solonchak,including three genera,Myxococcus,Cystobacter,and Anqiococcus.Furthermore,there were many culturable myxobacteria strains in flowing desert aeolian soils and all kinds of grey desert soil.The utilization types of soil had obvious influence on the distribution of myxobacteria.The number and species of myxobacterial trains from woodland samples were the most abundant.78.75% of the myxobacterial strains showed different degrees of antibiotic activity against potato late blight pathogen.The strain AL – 24 and AL – 10 with relatively high resistance were selected for the further research.It was shown that the two strains also exhibited different levels of growth-interfering activity against three major plant pathogens,Sclerotinia sclerotiorum,Fusarium oxysporum,and Rhizoctonia solani.In order to get more active substances,the fermentation condition of the strain AL-10 was optimized.The optimum fermentation condition of the strain was as follows:medium VY/2,resin 2%,inoculation amount 6%,bottle filling capacity 250 m L(500 m L),andfermentation time 5 d.The combined fermentation conditions of the strain AL-10 and AL-24 were also optimized.The antibiotic activity of the strain AL-24 against P.infestans reached its maximum level on the 7th day of fermentation after the assistant strain M-1 was added into the fermentation system when the strain AL-24 was cultured for 72 h.The antibiotic activity of the strain AL-10 against P.infestans had no obvious change before and after the assistant strain was added.The active substances of the two strains were insensitive to the change of temperature and sunlight exposure and were more stable in the p H 6-8 environment.The antibiotic activity of the active substances to P.infestans was affected by strong ultraviolet rays.In vitro experiments of detached potato leaves showed that the active substances of the two strains had good infection-preventing activity and weaker infection-treating activity against P.infestans.In this study,a preliminary study on the myxobacterium resources and their antibiotic activity against P.infestans in Alashan area of Inner Mongolia has been carried out,which lays a foundation for the development and utilization of the myxobacterium resources in the future.