Abstract
Iturins and closely related lipopeptides constitute a family of antifungal compounds known as iturinic lipopeptides that are produced by species in the Bacillus subtilis group. The compounds that comprise the family are: iturin, bacillomycin D, bacillomycin F, bacillomycin L, mycosubtilin, and mojavensin. These lipopeptides are prominent in many Bacillus strains that have been commercialized as biological control agents against fungal plant pathogens and as plant growth promoters. The compounds are cyclic heptapeptides with a variable length alkyl sidechain, which confers surface activity properties resulting in an affinity for fungal membranes. Above a certain concentration, enough molecules enter the fungal cell membrane to create a pore in the cell wall, which leads to loss of cell contents and cell death. This study identified 330 iturinic lipopeptide clusters in publicly available genomes from the B. subtilis species group. The clusters were subsequently assigned into distinguishable types on the basis of their unique amino acid sequences and then verified by HPLC MS/MS analysis. The results show some lipopeptides are only produced by one species, whereas certain others can produce up to three. In addition, four species previously not known to produce iturinic lipopeptides were identified. The distribution of these compounds among the B. subtilis group species suggests that they play an important role in their speciation and evolution.
Highlights
Iturins are an important class of lipopeptides that have been widely studied for their antibiotic activities and are produced by members of the Bacillus subtilis group (Ongena and Jacques, 2008)
The results show that 8 of the 11 species in the B. subtilis species group only make one iturinic compound (Figure 2), the analyses of the species that seemingly only make one compound are limited by the number of genomes available (i.e., Bacillus tequilensis, Bacillus nakamurai, Bacillus swezeyi, and “Bacillus genomospecies #1”)
It is well known that iturinic lipopeptides possess strong antifungal activity (Mhammedi et al, 1982; Peypoux et al, 1986; Ongena and Jacques, 2008; Ma et al, 2012; Guardado-Valdivia et al, 2018) and induce defense responses in plants (Farace et al, 2015; Park et al, 2016; Wu et al, 2018) which, in turn, has led to the commercialization of many Bacillus strains that manufacture these compounds (Dunlap, 2019)
Summary
Iturins are an important class of lipopeptides that have been widely studied for their antibiotic activities and are produced by members of the Bacillus subtilis group (Ongena and Jacques, 2008). Iturins were first reported as an antibiotic produced by B. subtilis in 1950 and named after the Ituri region in the Congo where the strain was isolated (Delcambe, 1950). Iturinic Lipopeptide Diversity in Bacillus plant pathogens (Ongena and Jacques, 2008). In addition to their antifungal activity, they have been shown to induce defense responses in plants (Farace et al, 2015; Park et al, 2016; Wu et al, 2018)
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