Fusaricidin C

Aims: LI-Fs are a family of highly potent cyclic lipodepsipeptide antibiotics with a broad antimicrobial spectrum (Gram-positive bacteria and fungi). In this study, LI-F-type antimicrobial peptides (AMP-jsa9) composing of LI-F03a, LI-F03b, LI-F04a, LI-F04b and LI-F05b were isolated from Paenibacillus polymyxa JSA-9. To better understand the antimicrobial mechanism of AMP-jsa9, the potency and action(s) of AMP-jsa9 against Bacillus cereus were examined. Methods and results: Flow cytometry, confocal laser microscopy, scanning electron microscopy, transmission electron microscopy (TEM) and atomic force microscopy observation, as well as determination of peptidoglycan and cell wall-associated protein and other methods were used. The results indicate that AMP-jsa9 exhibits strong, broad-spectrum antimicrobial activity. Moreover, AMP-jsa9 targets the cell wall and membrane of B. cereus to impair membrane integrity, increase membrane permeability and enhance cytoplasm leakage (e.g. K+ , protein, nucleic acid). This leads to bacterial cells with irregular, withered and coarse surfaces. In addition, AMP-jsa9 is also able to bind to DNA and break down B. cereus biofilms. Conclusions: In this study, the action mechanism of LI-Fs against B. cereus was clarified in details. Significance and impact of the study: The results of this study provide a theoretical basis for utilizing AMP-jsa9 or similar analogues as natural and effective preservatives in the food and feed industries. These efforts could also stimulate research activities interested in understanding the specific effects of other antimicrobial agents.

Fusaricidins B, C and D, new depsipeptide antibiotics, have been isolated as minor components from the culture broth of Bacillus polymyxa KT-8 which was obtained from the rhizosphere of garlic suffering from the basal rot caused by Fusarium oxysporum. The structure of fusaricidin B has been elucidated mainly by various NMR experiments coupled with amino acid analysis in relation to fusaricidin A, the main component of the complex, whose structure was reported previously. The fraction consisting of fusaricidins C and D was unsuccessfully separated, giving roughly a 4:1 mixture of the two, respectively. The structures of fusaricidins C and D have been determined within the mixture by detailed analyses of the 2D NMR spectra. Fusaricidins B, C and D are active against fungi and Gram-positive bacteria almost as well as fusaricidin A.

Fusaricidins produced by Paenibacillus polymyxa are lipopeptide antibiotics with outstanding antifungal activity. In this study, the whole gene cluster responsible for fusaricidin biosynthesis (fusA) was isolated and identified from the cDNA library of one biocontrol agent P. polymyxa SQR-21 (SQR-21). MALDI-TOF MS analysis confirmed that SQR-21 could produce four kinds of fusaricidins: A, B, C, and D. A central promoter that drove the transcription of fusGFEDCBA was revealed by mapping of the fus promoter region by 5' deletions. The disruption of fusA in SQR-21 led to the abolishment of fusaricidin production and antifungal activity. The direct interaction between a potential regulator, AbrB, and the promoter region of fus gene cluster was confirmed by electrophoretic mobility shift assays. One abrB disruption mutant showed significantly higher antifungal activity compared with the wild type. These results revealed a pathway for the transcriptional regulation of the fus gene cluster in P. polymyxa.