Identification of an antagonistic strain Bacillus amyloliquefaciens E3 against Dickeya zeae and its antimicrobial activity

Objective  To isolate and identify Bacillus amyloliquefaciens strain which can inhibit the growth of Dickeya zeae EC1 from the rhizosphere soil of citrus plants, and analyze its antibacterial mechanism.

Method  The B. amyloliquefaciens E3 strain antagonizing the growth of D. zeae EC1 was screened from the rhizosphere soil by plate diffusion method. The E3 strain was classified and identified based on colony phenotype, physiological and biochemical characteristics of bacteria and 16S rDNA sequence analysis. Effects of E3 sterile culture medium on the seeds germination ability of rice infected by D. zeae EC1 was detected. The crude lipopeptides of E3 strain was extracted by hydrochloric acid precipitation combined with acetone extraction. The antimicrobial activity of crude lipopeptides against pathogenic fungi were determined by plate confrontation method. The antimicrobial activity of crude lipopetides against pathogenic bacteria were determined by agar diffusion method, and the minimum inhibitory concentration (MIC) was obtained. The crude lipopeptides were separated and purified by HPLC with Durashell C18 column. Liquid chromatography-mass spectrometry (LC-ESI-MS) analysis was used to identify the molecular weights of the antimicrobial substances and speculate its chemical composition.

Result  B. amyloliquefaciens E3 strain had an inhibitory effect against Fusarium solani, D. zeae MS1 and Ralstonia solanacearum, etc, indicating that it had broad-spectrum resistance. The sterile culture medium of B. amyloliquefaciens E3 strain inhibited the infection of germinating rice seeds by D. zeae EC1 and significantly increased the seed germination rate. The crude lipopeptides of E3 strain inhibited the growth of D. zeae EC1 with the MIC of 348.97 µg/mL. HPLC combined with LC-ESI-MS analysis showed that the main antibacterial substances secreted by E3 strain included surfactin, fengycin and iturin.

Conclusion  The B. amyloliquefaciens E3 strain is potential to be a biocontrol agent. It can antigonize a variety of plant pathogens such as D. zeae EC1, R. solanacearum and F. solani by secreting three kinds of lipopeptides including surfactin, fengycin and iturin. The results provide a theoretical basis for the application of B. amyloliquefaciens E3 in biological control.