Study on Selective Isolation and Antibiotic Activity of Rare Actinomycetes from Soil

Based on an improved selective isolation techniques,31 soil sample collected from Anhui,Zhejiang,Shandong,Shaanxi et al provinces of China were screened .The result showed that when use the improved HV agar as the isolation medium,dilute the soil sample 100 times and use 2×10-5 g/mL potassium dichromate plus 2×10-5 g/mL nalidixic acid plus 1×10-5 g/mL kanamycin as inhibitor,the isolation was the best.All the fermentation of the screened 417 strains were tested against the plant pathogenic fungi,such as Bipolaris sorokiniana,Exserohilum turcicum,Alternaria alternata,and pathogenic bacteria,such as Bacillus subtilis,Escherichia coli,Staphylococcus aureus.Five of them have been proven to produce bioactive metabolites,which were labeled as H32,H75,H223, H227,H238,respectively . By means of mycelium growth rate , the fermentations of H223 and H238 showed the best inhibitive action,both EC50 value swere were less than 10 mL/L.Spore germination tests showed that the fermentation of H32 exhibited the strongest antibiotic activity against Bipolaris sorokiniana,Exserohilum turcicum,Alternaria alternata,the EC50 values were 25.5,28.9,29.9 mL/L,respectively.Cup-plate tests indicated that the fermentations of the 5 strains had significant activities against B.subtilis,E.coli,S.aureus,and the inhibitive diameters of the fermentation of strain H223 to the 3 bacteria were all more than 30 mm.Pot tests on B.graminis exhibited that the protective efficacy of fermentations of the 5 strains were 73.45％ ~82.35％,therapeutic efficacy were 67.74％ ~70.80％.