Structural and Functional Insights into Iturin W, a Novel Lipopeptide Produced by the Deep-Sea Bacterium Bacillus sp. Strain wsm-1

In the present study, a deep-sea bacterial strain designated Bacillus sp. strain wsm-1 was screened and found 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 homologs, which were different from any previously reported lipopeptides, were identified to possess identical amino acid sequences of β-amino fatty acid-Asn-Ser-Asn-Pro-Tyr-Asn-Gln and deduced as two novel lipopeptides designated C(14) iturin W and C(15) iturin W. Electron microscopy observation indicated that both iturin W homologs caused obvious morphological changes and serious disruption of plasma membrane toward fungal cells, while C(15) iturin W exhibited more serious cell damages than C(14) iturin W did, which was well consistent 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 C(14) iturin W and C(15) iturin W were investigated. The results indicated that supplements of most of the detected carbon and nitrogen sources could increase the yield of C(14) iturin W, but inhibit the yield of C(15) iturin W, while supplements of tryptone and most of the detected amino acids could increase the yield of both C(14) iturin W and C(15) 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. Biological control of plant diseases by microbial natural products is more desirable than traditional chemical control. In this study, we discovered a novel lipopeptide, iturin W, with promising prospects in biological control of plant diseases. Moreover, the effects of different carbon and nitrogen sources and amino acids on production of C(14) iturin W and C(15) iturin W would provide a reasonable basis for the optimization of the fermentation process of lipopeptides. Notably, the structure of iturin W was different from that of any previously reported lipopeptide, suggesting that deep-sea microorganisms might produce many novel natural products and have significant potential in the development of biological products in the future.