The Biologically Important Surfactin Lipopeptide Induces Nanoripples In Supported Lipid Bilayers

Under specific conditions, lipid membranes form ripple phases with intriguing
nanoscale undulations. Here, we show using in situ atomic force microscopy (AFM)
that the biologically important surfactin lipopeptide induces nanoripples of 30
nm periodicity in dipalmitoyl phosphatidylcholine (DPPC) bilayers at 25 degrees
(i.e. well below the pretransition temperature of DPPC). Whereas most undulations
formed the classical straight orientation with characteristic angle changes of
120 degrees , some of them also displayed unusual circular orientations.
Strikingly, ripple structures were formed at 15% surfactin but were rarely or
never observed at 5 and 30% surfactin, emphasizing the important role played by
the surfactin concentration. Theoretical simulations corroborated the AFM data by
revealing the formation of stable surfactin/lipid assemblies with positive
curvature.