Effects of dirhamnolipid on the structural properties of phosphatidylcholine membranes

Effects of a bacterial trehalose lipid on phosphatidylglycerol membranes

Bacterial trehalose lipids are biosurfactants with potential application in the biomedical/healthcare industry due to their interesting biological properties. Given the amphiphilic nature of trehalose lipids, the understanding of the molecular mechanism of their biological action requires that the interaction between biosurfactant and membranes is known. In this study we examine the interactions between a trehalose lipid from Rhodococcus sp. and dimyristoylphosphatidylglycerol membranes by means of differential scanning calorimetry, X-ray diffraction, infrared spectroscopy and fluorescence polarization. We report that there are extensive interactions between trehalose lipid and dimyristoylphosphatidylglycerol involving the perturbation of the thermotropic gel to liquid-crystalline phase transition of the phospholipid, the increase of fluidity of the phosphatidylglycerol acyl chains and dehydration of the interfacial region of the bilayer, and the modulation of the order of the phospholipid bilayer. The observations are interpreted in terms of structural perturbations affecting the function of the membrane that might underline the biological actions of the trehalose lipid.

Effect of rhamnolipids on pulmonary surfactant foam films

The effect of a rhamnolipid biosurfactant on pulmonary surfactant is studied employing the black foam film method. Pulmonary surfactant is modeled by a commercially available lung surfactant preparation (LSP). The effect of rhamnolipid concentration on the formation and stability of films formed from mixtures of LSP and rhamnolipids is experimentally studied by measurements of the probability W of formation of black foam films as a function of both LSP and rhamnolipid concentrations at the physiologically relevant electrolyte concentration C(el) = 0.15 mol dm(-3) NaCl. The obtained curves show that addition of rhamnolipid at a concentration C(RhL) = C(c) (critical concentration of black foam film formation) to LSP suspensions causes destabilization of the foam films. In this case, additional quantities of lung surfactant preparation are needed to obtain black films with probability W = 100%. Rhamnolipid adsorption and formation of mixed adsorbed layers at the solution/air interfaces of foam films formed from mixtures of lung surfactant and rhamnolipids are experimentally studied by monitoring the effect of electrolyte and rhamnolipid concentrations on the thickness h of the foam films. The incorporation of rhamnolipid ions in the adsorbed layers at the film interfaces is evidenced also by direct measurements of the disjoining pressure Pi in the films. The Pi(h) isotherms demonstrate that the added rhamnolipids change the surface electric parameters of the films and their thickness and stability at higher pressures. The obtained results show that the different molecular components in the mixture and the increased surface charge at the film interfaces originating from the rhamnolipid ions have a significant effect on the surface forces operative in the studied films.

Hemolytic activity of a bacterial trehalose lipid biosurfactant produced by Rhodococcus sp.: evidence for a colloid-osmotic mechanism

A succinoyl trehalose lipid produced by Rhodococcus sp. behaves as a biological surfactant and also displays various interesting biological activities. Trehalose lipid has been shown to have a great tendency to partition into phospholipid membranes; therefore, the characterization of its interaction with biological membranes is of central importance. In this work, human red blood cells have been used as an experimental model. Trehalose lipid causes the swelling of human erythrocytes followed by hemolysis at concentrations well below its critical micellar concentration. Kinetic measurements show that, upon addition of trehalose lipid, K(+) release precedes that of hemoglobin. Osmotic protectants of the appropriate size added to the external medium make it possible to avoid hemolysis. The results indicate that trehalose lipid causes the hemolysis of human erythrocytes by a colloid-osmotic mechanism, most likely by formation of enhanced permeability domains, or "pores" enriched in the biosurfactant, within the erythrocyte membrane. Scanning electron microscopy shows trehalose lipid-induced spherocytosis and echinocytosis of red blood cells, which fits well within the framework of the bilayer-couple hypothesis. The presented results contribute to establishing a molecular basis for the biological properties of this trehalose lipid biosurfactant.

Mechanism of membrane permeabilization by a bacterial trehalose lipid biosurfactant produced by Rhodococcus sp

The interactions of a succinoyl bacterial trehalose lipid biosurfactant produced by Rhodococcus sp. with phospholipid vesicles, leading to membrane permeabilization, are studied by means of calorimetric and fluorescence and absorption spectroscopical techniques in search for a molecular model. The critical micelle concentration (CMC) of trehalose lipid is determined, by surface tension measurements, to be 300 muM. Binding of trehalose lipid to palmitoyloleoylphosphatidylcholine membranes is studied by means of isothermal titration calorimetry. The partition constant, in conjunction with the CMC, indicates that trehalose lipid behaves as a weak detergent, which prefers membrane incorporation over micellization. Addition of trehalose lipid to palmitoyloleoylphosphatidylcholine large unilamellar vesicles results in a size-selective leakage of entrapped solutes to the external medium. Experimental evidence is provided to support the requirement of a stage of flip-flop prior to membrane permeabilization, and the rate of flip-flop is measured using fluorescent probes assays. The lipid composition of the target membrane is found to modulate the leakage process to a great extent. It is proposed that trehalose lipid incorporates into phosphatidylcholine membranes and segregates within lateral domains which may constitute membrane defects or "pores", through which the leakage of small solutes might take place. The results presented here contribute to the knowledge of the molecular mechanisms underlying the membrane-related biological actions of this bacterial trehalose lipid biosurfactant.

Interactions of a bacterial biosurfactant trehalose lipid with phosphatidylserine membranes

Trehalose lipids are biosurfactants produced by rhodococci that, in addition to their well known potential industrial and environmental uses, are gaining interest in their use as therapeutic agents. The study of the interaction of biosurfactants with membranes is important in order to understand the molecular mechanism of their biological actions. In this work we look into the interactions of a bacterial trehalose lipid produced by Rhodococcus sp. with dimyristoylphosphatidylserine membranes by using differential scanning calorimetry, X-ray diffraction and infrared spectroscopy. Differential scanning calorimetry and X-ray diffraction show that trehalose lipid broadens and shifts the phospholipid gel to liquid-crystalline phase transition to lower temperatures, does not modify the macroscopic bilayer organization and presents good miscibility both in the gel and the liquid-crystalline phases. Infrared experiments show that trehalose lipid increases the fluidity of the phosphatidylserine acyl chains, changed the local environment of the polar head group, and decreased the hydration of the interfacial region of the bilayer. Trehalose lipid was also able to affect the thermotropic transition of dimyristoylphosphatidyserine in the presence of calcium. These results support the idea that trehalose lipid incorporates into the phosphatidylserine bilayers and produces structural perturbations which might affect the function of the membrane.

Interactions of a Rhodococcus sp. biosurfactant trehalose lipid with phosphatidylethanolamine membranes

Trehalose lipids are an important group of glycolipid biosurfasctants mainly produced by rhodococci. Beside their known industrial applications, there is an increasing interest in the use of these biosurfactants as therapeutic agents. We have purified a trehalose lipid from Rhodococcus sp. and made a detailed study of the effect of the glycolipid on the thermotropic and structural properties of phosphatidylethanolamine membranes of different chain length and saturation, using differential scanning calorimetry, small and wide angle X-ray diffraction and infrared spectroscopy. It has been found that trehalose lipid affects the gel to liquid crystalline phase transition of phosphatidylethanolamines, broadening and shifting the transition to lower temperatures. Trehalose lipid does not modify the macroscopic bilayer organization of saturated phosphatidylethanolamines and presents good miscibility both in the gel and the liquid crystalline phases. Infrared experiments evidenced an increase of the hydrocarbon chain conformational disorder and an important dehydrating effect of the interfacial region of the saturated phosphatidylethanolamines. Trehalose lipid, when incorporated into dielaidoylphosphatidylethanolamine, greatly promotes the formation of the inverted hexagonal HII phase. These results support the idea that trehalose lipid incorporates into the phosphatidylethanolamine bilayers and produces structural perturbations which might affect the function of the membrane.

Thermodynamic and structural changes associated with the interaction of a dirhamnolipid biosurfactant with bovine serum albumin

The interaction of a dirhamnolipid biosurfactant secreted by Pseudomonas aeruginosa with bovine serum albumin was studied by means of various physical techniques. Binding of the biosurfactant to bovine serum albumin was first characterized by isothermal titration calorimetry, showing that one or two molecules of dirhamnolipid, in the monomer state, bound to one molecule of the protein with high affinity. These results were confirmed by surface tension measurements in the absence and presence of bovine serum albumin. As seen by differential scanning calorimetry, dirhamnolipid shifted the temperature of the thermal unfolding of bovine serum albumin toward higher values, thus increasing the stability of the protein on heating. The impact of dirhamnolipid on the structure of the native protein was low, since most of the secondary structure remained unaffected upon interaction with the biosurfactant, as shown by FTIR spectroscopy. However, 2D correlation infrared spectroscopy indicated that the sequence of temperature-induced structural changes in native bovine serum albumin was modified by the presence of the biosurfactant. The consequences of these results in relation to possible applications of these dirhamnolipid biosurfactants for protein studies are discussed.

Surface forces and properties of foam films from rhamnolipid biosurfactants

Foam films are considered as a convenient model to study the interaction behaviour and surface properties of microbial rhamnolipid type biosurfactants. The Scheludko-Exerowa microinterferometric methodology of film thickness measurements is employed for experimental studies of microscopic foam films formed from aqueous solutions of a single rhamnolipid Rh1 (with one rhamnosyl head group) and of mixtures of rhamnolipid surfactants Rh1 and Rh2 (with two rhamnosyl head groups) at ratios Rh2/Rh1=1.2 and Rh2/Rh1=0.69. The measurements of the equilibrium thickness (h) of the obtained films as a function of surfactant concentration (Cs) and electrolyte (NaCl) concentration (C el) determine the conditions for obtaining common, common black and Newton black films. The saturation values of the diffuse electric layer potential phi 0 approximately 60 mV for the Rh1.2 and phi 0 approximately 94 mV for the Rh0.69 common films conform the ionic character of the rhamnolipids. The h(C el) curves of the rhamnolipid foam films and the directly measured disjoining pressure (Pi(h)) isotherms indicate the ranges of action of the DLVO and non-DLVO surface forces. The obtained foam film parameters allow their practical use in ecology and in various technological processes where rhamnolipid surfactants are used. Experiments with model lung surfactant (Infasurf) foam films with rhamnolipid added outline a perspective for the potential application of the foam film for investigating the effect of rhamnolipids on human alveoli.

Domain formation by a Rhodococcus sp. biosurfactant trehalose lipid incorporated into phosphatidylcholine membranes

The study of the interaction of biosurfactants with biological membranes is of great interest in order to gain insight into the molecular mechanisms of their biological actions. In this work we report on the interaction of a bacterial trehalose lipid produced by Rhodococcus sp. with phosphatidylcholine membranes. Differential scanning calorimetry measurements show a good miscibility of the glycolipid in the gel state and immiscibility in the fluid state, suggesting domain formation. These domains have been visualized and characterized, for the first time, by scanning force microscopy. Incorporation of trehalose lipid into phosphatidylcholine membranes produces a small shift of the antisymmetric stretching band toward higher wavenumbers, as shown by FTIR, which indicates a weak increase in fluidity. The C=O stretching band shows that incorporation of trehalose lipid increases the proportion of the dehydrated component in mixtures with the three phospholipids at temperatures below and above the gel to liquid-crystalline phase transition. This dehydration effect is also supported by data on the phospholipid P=O stretching bands. Small-angle X-ray diffraction measurements show that in the samples containing trehalose lipid the interlamellar repeat distance is larger than in those of pure phospholipids. These results are discussed within the frame of trehalose lipid domain formation, trehalose lipid/phospholipid interactions and its relevance to membrane-related biological actions.

Aggregation behaviour of a dirhamnolipid biosurfactant secreted by Pseudomonas aeruginosa in aqueous media

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.