ESI-Q-TOF MS analysis further revealed the amino acid sequence of fraction 1.The
resulting fragmentation spectrum was analyzed, revealing a partial
series of a-type and b-type ions covered the entire amino acid
sequence of the peptide. The sequences indicated that Ser and Asn
were connected to a fatty acid moiety, and the molecule was
deduced to be a cyclic lipopeptide based on data obtained through
tandem mass spectrometry regulation. This sequence was found to
be N-Ser-Asn-Pro-Gln-Asn-Tyr-Asn-C. Based on an analysis of its
cyclic structure, the lipopeptide was determined to be iturin A
(Fig. 7). The molecular mass and complete peptide sequence were
similar to those of iturin A, produced by B. amyloliquefaciens TF28
(Zhang et al., 2012). Altogether, iturin A was identified as an
inhibitor of B. dothidea.