Production of iturin A by Bacillus amyloliquefaciens suppressing Rhizoctonia solani

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 showed 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 those obtained using 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.