Abstract
Bacillus subtilis strain QST713 produces a unique combination of lipopeptides from the surfactin (SF), fengycin (FE) and iturin (IT) families. The fungicidal activity of this peptide mix is used by a biopesticide for crop protection and believed to be based on the permeabilization of target membranes by the peptides. To shed light on the activity, selectivity and synergisms of the peptides, we have studied their membrane binding and the subsequent effects on the structure and dynamics of the membrane. We measured the time-resolved fluorescence and fluorescence anisotropy of intrinsic tyrosine and hydrophobic dyes (e.g., DPH), time-resolved dipolar relaxation of Laurdan, interaction thermodynamics by ITC, and size and zeta potential of vesicles by DLS. The results are compared with the effects of synthetic surfactants and provide valuable information about the molecular background of the very unusual leakage and lysis behaviour of the lipopeptides.
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