Isolation And Screening Of Antagonistic Actinomycects From Soil

In this study, 422 strains of actinomycetes were isolated from 43 soil samples collected from various areas with different vegetation at different altitude in 6 provinces of China. The main results are as follows:The antimicrobial activities of actinomycetes isolated from soil were tested the bioactivities. In vitro, the results of bioassay indicated that the fermentation broths of the 28 strains had remarkable inhibition activities against bacteria. Of those, only the fermentation broths of strains N74, N179, N331 and N393 exhibited inhibition activities against plant pathogenic fungi. The results of mycelium growth rate tests indicated that the fermentation products of N331 and N393 had higher inhibition activities than strains N74 and N179. To be more precise, the EC50 values of N74 and N179 against all pathogenic fungi were lower than 23 mL·L-1, and the EC50 values of N331 and N393 were lower than 15 mL·L-1. The fermentation broths of those 4 strains also inhibited the spore germination of Curvulavia lunata, Fusarium oxysporum, Bipolaris sorokiniana, Pseudoperonospora cubensis, and EC50 of N331 against P. cubensis was 7.5mL·L-1, the EC50 values of N393 against P. cubensis and F. oxysporum were 9.9mL·L-1 and 1.8mL·L-1, respectively. The results of the pot plant tests showed that the fermentation broths of strains N331 and N393 exhibited higher efficacy than strains N74 and N179 against P.cubensis, the protective and therapeutic efficacy of N7, N179, N331 and N393 were 26.9% and 22.6%, 44.6% and 33.9%, 97.4% and 83.3, 85.6% and 59.3%, respectively.The results of the stability tests indicated that antimicrobial activity of the fermentation broth of strains N74, N179, N331 and N393 had few variety when they were cultivated 9 generations. The fermentation broths of those 4 strains were stable to high temperature except N47, but none of them was stable to acid or alkali.By means of observation on substrate mycelium, aerial mycelium, spore and sporothrix, cultural, and physiological characteristics, N74, N179, N331 and N393 are proposed as close or variety species of Streptomyces sparsogenes var.sparsogenes, Stretomyces.akiyoshiensis, Micromonos pora pallida, Streptomyces parvullus, respectively.