Recovery of several cell pellet‐associated antibiotics produced by Bacillus amyloliquefaciens NJN‐6

In this study, six antibiotics which are antagonistic to phytopathogens were extracted from the water-washed cell pellets of Bacillus amyloliquefaciens NJN-6. They were purified by HPLC and identified using electrospray ionization mass spectroscopy (ESI-MS). Besides three iturin A homologous and macrolactin A, two other kinds of antibiotics were extracted from the cell pellets of B. amyloliquefaciens NJN-6. An antifungal compound with the molecular mass of 1072 Da was identified as bacillomycin D, and the antibacterial compound with the molecular mass of 400 Da was identified as macrolactin E. We also quantified iturin A in both cell pellets and culture media, and the concentrations were 751·12 mg kg−1 and 21·02 mg l−1, respectively. These results show that in addition to the culture medium, the cell pellets could also be a potential resource for antibiotics and the strain B. amyloliquefaciens NJN-6 might be an attractive source for antibiotic production and an antagonist for plant diseases. Significance and Impact of the Study The novelty of this work is the production of several antimicrobial substances associated with cell pellets and the production of antibiotic macrolactin E by B. amyloliquefaciens strain. Here, cell pellet-associated antimicrobial compounds were identified, and strain NJN-6 was able to produce three cell pellet-associated iturin A family homologues, bacillomycin D, macrolactin A and macrolactin E. With the exception of macrolactin E, all other antimicrobial compounds were identified in the liquid culture. The production of macrolactin E by any B. amyloliquefaciens strain has not been previously reported; therefore, this is the first report about macrolactin E production by B. amyloliquefaciens.