title: Aggregation behaviour of a dirhamnolipid biosurfactant secreted by Pseudomonas aeruginosa in aqueous media.
abstract: The process of micelle formation, along with the formation of higher order aggregates, is described for a dirhamnolipid extracellular biosurfactant secreted by Pseudomonas aeruginosa. As determined by surface tension measurements, at pH 7.4 the CMC of dirhamnolipid is 0.110 mM, whereas at pH 4.0 it falls to 0.010 mM, indicating that the negatively charged diRL has a much higher CMC value than the neutral species. Centrifugation and dynamic light scattering measurements show formation of larger aggregates at concentrations above the CMC. These aggregates have been shown by electron microscopy to be mainly multilamellar vesicles of heterogeneous size. X-ray scattering gave a value of 32 A for the interlamellar repeat distance of these vesicles. Taking into account the experimental data, a molecular modelling of the dirhamnolipid moiety has been carried out, which details the size of the hydrophilic and hydrophobic portions, and suggests the possible intermolecular interactions responsible for the stabilisation of dirhamnolipid aggregates. The relevance of this aggregation behaviour is discussed with respect to the molecular basis of its activities.
authors.affiliation: Departamento de Bioquímica y Biología Molecular-A, Facultad de Veterinaria, Universidad de Murcia, E-30100 Murcia, Spain.
authors.forename: Marina
authors.initials: M
authors.lastname: Sánchez
authors.forename: Francisco J
authors.initials: FJ
authors.lastname: Aranda
authors.forename: María J
authors.initials: MJ
authors.lastname: Espuny
authors.forename: Ana
authors.initials: A
authors.lastname: Marqués
authors.forename: José A
authors.initials: JA
authors.lastname: Teruel
authors.forename: Angeles
authors.initials: A
authors.lastname: Manresa
authors.forename: Antonio
authors.initials: A
authors.lastname: Ortiz
mesh_terms: D006017:Glycolipids / Q000737:chemistry* / Q000378:metabolism; D008823:Micelles; D008854:Microscopy, Electron; D008958:Models, Molecular; D015394:Molecular Structure; D011550:Pseudomonas aeruginosa / Q000378:metabolism*; D012542:Scattering, Radiation; D013500:Surface Tension; D013501:Surface-Active Agents / Q000737:chemistry* / Q000378:metabolism; D053835:Unilamellar Liposomes / Q000737:chemistry*; D014867:Water / Q000737:chemistry
chemical_list: D006017:Glycolipids; D008823:Micelles; D013501:Surface-Active Agents; D053835:Unilamellar Liposomes; C051310:rhamnolipid hemolysin, Pseudomonas aeruginosa; D014867:Water