Submitted to: Soil Biology and Biochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/31/2001
Publication Date: N/A
Interpretive Summary: Rhizoctonia solani, a soilborne fungus, causes pre- and postemergence damping-off of soybean which can reduce seedling stands and yield. Several microorganisms antagonistic to R. solani have been studied for biocontrol of this pathogen including strains bacterial species of Bacillus. Antibiotic production by some bacteria plays a major role in disease suppression and members of the genus Bacillus produce a variety of antibacterial and antifungal peptide antibiotics. Bacillus amyloliquefaciens strain B94 was used as a biocontrol agent to suppress Rhizoctonia solani and other fungal plant pathogens. The goal of this study was to purify and identify certain antibiotics produced by this strain using chromatographic, mass spectrometer, and other chemical analytical techniques. Three major antifungal compounds were purified from its culture broth. A new reliable method for isolation and purification of these compounds from bacterial broth culture was developed. Identification of the antibiotics produced may improve our understanding of the mechanism involved in this and other biocontrol systems. This research will be of primary interest to other researchers studying antifungal compounds.
Technical Abstract: Bacillus amyloliquefaciens strain B94 was used as a biocontrol agent to suppress Rhizoctonia solani and other fungal plant pathogens. Three major antifungal compounds were purified from its culture broth, each has an amino acid composition consisting of Asn, Gln, Ser, Pro, and Tyr in a molar ratio of 3:1:1:1:1. Fast atom bombardment mass spectrometry/mass spectrometry (FAB MS/MS) collision induced dissociation (CID) analysis show that the antifungal compounds were three isomers of iturin A, a cyclic lipopeptide antibiotic produced by Bacillus subtilis. One of the major compounds with a molecular weight of 1042.5533 was identified as iturin A2. The peptide backbone of this compound was opened chemically, and the resulting linear peptide partially sequenced using the Edman degradation method. The results confirmed the results of FAB MS/MS CID analysis. A new reliable method for isolation and purification of iturin A and related compounds from bacterial broth culture was developed. The CID spectrum of iturin A could be used as a "fingerprint" to identify iturin A in a variety of mixtures.