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Surfactin; Mixed DMPC–surfactin-micelles; Cryo-electron microscopy; Cryo-electron tomography
Abstract:
Vesicles of L-α-dimyristoyl-phosphatidylcholine (DMPC) are known to disintegrate upon treatment with surfactin, a lipoheptapeptide biosurfactant from Bacillus subtilis OKB 105, as was observed by static light scattering (SLS) and cryo-transmission electron microscopy (cryo-TEM) recently. The lysis of DMPC bilayers occurs strongly dependent on the surfactin concentration according to a three-stage model. Unilamellar DMPC vesicles are disrupted to form sheet-like lamellar intermediates at a moderate surfactant concentration, but undergo a transition towards smaller particles of unknown structure at a higher surfactant concentration according to earlier neutron scattering experiments. Here we present direct structural evidence from cryoelectron tomography data that thread-like micelles with a uniform diameter of 6.5 nmare organized into loops of different sizes at a surfactin concentration of >15 mol%.
