A study on the interactions of surfactin with phospholipid vesicles

Surfactin, an acidic lipopeptide produced by various strains of Bacillus su btilis, behaves as a very powerful biosurfactant and posses several other i nteresting biological activities. By means of differential scanning calorim etry and X-ray diffraction the effect of surfactin on the phase transition properties of bilayers composed of different phospholipids, including lipid s forming hexagonal-H-II phases, has been studied. The interactions of surf actin with phosphatidylcholine and phosphatidylglycerol seem to be optimal in the case of myristoyl acyl chains, which have a similar length to the su rfactin hydrocarbon tail. Data are shown that support formation of complexe s of surfactin with phospholipids. The ionized form of surfactin seems to b e more deeply inserted into negatively charged bilayers when Ca2+ is presen t, also supporting the formation of surfactin-Ca2+ complexes. In mixtures w ith dielaidoylphosphatidylethanolamine, a hexagonal-H-II phase forming lipi d, surfactin displays a bilayer stabilizing effect. Our results are compati ble with the marked amphiphilic nature of surfactin and may contribute to e xplain some of its interesting biological actions; for instance the formati on of ion-conducting pores in membranes. (C) 1999 Elsevier Science B.V. All rights reserved.