In the present study, a deep-sea bacterial strain designated Bacillus sp. wsm-1 was screened to exhibit strong antifungal activity against many plant pathogenic fungi, and corresponding antifungal agents were thereby purified and determined by tandem mass spectrometry to be two cyclic lipopeptide homologs. These two lipopeptide homologs were identified to possess identical amino acid sequences of β-amino fatty acid-Asn-Ser-Asn-Pro-Tyr-Asn-Gln, which were different from any previously reported lipopeptides, and deduced as two novel lipopeptides designated as C14 iturin W and C15 iturin W, respectively. Electron microscopy observation indicated that both iturin W homologs caused obvious morphological changes and serious disruption of plasma membrane toward fungal cells, while C15 iturin W exhibited more serious cell damages than C14 iturin W did, which was consistent well with the results of the antifungal activity assays. To improve the yield and antifungal activity of iturin W, the effects of different carbon and nitrogen sources and amino acids on production of C14 iturin W and C15 iturin W were investigated, respectively. The results indicated that supplements of most of the detected carbon and nitrogen sources could increase the yield of C14 iturin W, but inhibit the yield of C15 iturin W, while supplements of tryptone and most of the detected amino acids could increase the yield of both C14 iturin W and C15 iturin W.
IMPORTANCE Plant disease caused by pathogenic fungi is one of the most devastating diseases, which affects the food safety of the whole world to a great extent. Compared with traditional chemical control, biological control of plant diseases by microbial natural products is more desirable. In this study, we discovered a novel lipopeptide iturin W with promising prospect in biological control of plant diseases. Moreover, the effects of different carbon and nitrogen sources and amino acids on production of C14 iturin W and C15 iturin W would provide a reasonable basis for the optimization of fermentation process of lipopeptides. Notably, the structure of iturin W was different to any previously reported lipopeptides, suggesting deep-sea microorganisms might produce many novel natural products and have significant potentials to develop biological products in the future.