Understanding the Fungicidal Activity of Lipopeptides on the Basis of their Biosurfactant Properties

Abstract

Bacillus subtilis strain QST 713 produces a wide variety of lipopeptides of the surfactin, iturin, and fengycin families. These lipopeptides are believed to be produced to attack other organisms by permeabilizing their cell membranes. In order to do that, these peptides have to induce membrane pore or leaks and at even higher concentration they may solubilize the membrane. We are interested in a better understanding of the fungicidal activity of the organism, which has been utilized for the highly effective and environmentally safe protection of crops against a variety of pathogens. We have been studying the destabilization, permeabilization and lysis of lipid vesicles by the peptides by means of isothermal titration calorimetry, the lifetime- based vesicle leakage assay, light scattering, and other methods. We find fundamentally different lytic effects of the different classes and synergistic activity on various membrane types. In this study, we have addressed the mechanism of action and surfactant like properties for the extreme lytic activity of these compounds, the interplay between the different peptides in the biologically optimized mixture, and the selectivity of the action to different lipid membranes.