Antibacterial activity against Ralstonia solanacearum of the lipopeptides secreted from the Bacillus amyloliquefaciens strain FJAT-2349

Aims The aims of this study were to identify the structure of antibacterial lipopeptide (LP) produced by Bacillus amyloliquefaciens strain FJAT-2349, to analyse the effects of the culture medium and temperature on LP production and to assess the biocontrol efficiency of the LPs against tomato bacterial wilt. Methods and Results Lipopeptides were extracted by acid precipitation and resolved in methanol and their structure was identified through LC-QTOF-MS/MS method. The antibacterial activities of the LPs were evaluated through inhibition zone experiments. The biocontrol efficiency of the LPs against tomato bacterial wilt was examined by a pot test. The LPs were composed of iturin (C-14-C-17 iturin A), fengycin (C-14/C-16 fengycin A, C-14 fengycin B-2, C-16 fengycin A(2)/B-2, C-16-C-17 fengycin B, C-15 fengycin A derivatives and C-15 fengycin B derivatives) and surfactin (C-12-C-16 surfactin A). Moreover, the composition of the LPs was significantly influenced by the culture medium and temperature; the contents of iturin, fengycin and surfactin varied within the range from 0 center dot 41-5 center dot 89, 4 center dot 54-181 center dot 67 and 2 center dot 05-19 center dot 65 mg l(-1) in the different culture media and from 0 center dot 39-11 center dot 04, 1 center dot 45-215 center dot 14 and 7 center dot 79-24 center dot 43 mg l(-1) under different culture temperatures respectively. The results indicated that the contents of the LP mixture, fengycin and surfactin secreted from FJAT-2349 all decreased along with an increasing culture temperature. The fermentation supernatants and LP extracts had the strongest inhibition activities of Ralstonia solanacearum when strain FJAT-2349 was incubated at 25 degrees C using potato dextrose broth as the culture medium among all the assayed culture conditions. The purified fengycin was found to be the active antibacterial compound against R. solanacearum, but the purified surfactin was not. The pot experiments demonstrated that the LPs secreted from the strain FJAT-2349 could effectively control the tomato bacterial wilt with a biocontrol efficiency of 97 center dot 6%. Conclusions The LPs secreted from strain FJAT-2349 could serve as potential biocontrol agents against tomato bacterial wilt. Significance and Impact of the Study The LPs exhibited good potential applications in the biocontrol of tomato bacterial wilt.