| In this experiment,76 strains of Bacillus subtilis were isolated from soil samples collected from Huai'an aquaculture base.A strain JCL16 with the best antagonistic effect on Nocardia seriolaes was screened out.Using the Nocardia seriolaes as indicator bacteria,the bacteriostatic diameter of the strain JCL16 was 17.1±0.3 mm.The bacteriostatic diameter of the sample was15.8±0.4 mm after filtration,indicating that its antibacterial activity was related to the cell and secondary metabolites.The secondary metabolites of JCL16 strain were detected to be surfactant,bacteriolysin and Subtilisin A by HPLC-MS,the yield was 18 mg/L,14 mg/L and 10 mg/L.The diameter of bacteriostatic circle was 10.1±0.3 mm,14.7±0.5 mm and 10.4±0.3 mm respectively.It was found that the three kinds of secondary metabolites mixed in different proportion had synergistic effect on antagonistic pathogens.The mutant library was constructed by randomly transferring p Mar A,a shuttle vector carrying Tn YLB-1,into JCL16 strain.The average transformation efficiency of p Mar A plasmid was 3.17x10-8,and the average transposition efficiency was 95.1%.In this paper,2000 mutant strains of were screened.The results showed that 180 strains increased the antibacterial activity,650 strains decreased the antibacterial activity and 1170 strains kept the diameter of the antibacterial circle unchanged.Among the 40 strains with significant changes in antibacterial activity,21 strains increased the diameter of bacteriostatic circle by more than 30%,19 strains decreased by more than 50%.The mutant with the highest diameter of bacteriostatic circle was named H5,and the production of H5 surfactant was 24 mg/L. |
PDF Full Text Request