Aqueous-phase behavior of natural glycolipid biosurfactant mannosylerythritol lipid A: sponge, cubic, and lamellar phases

Promising Application, Efficient Production, and Genetic Basis of Mannosylerythritol Lipids

Mannosylerythritol lipids (MELs) are a class of glycolipids that have been receiving increasing attention in recent years due to their diverse biological activities. MELs are produced by certain fungi and display a range of bioactivities, making them attractive candidates for various applications in medicine, agriculture, and biotechnology. Despite their remarkable qualities, industrial-scale production of MELs remains a challenge for fungal strains. Excellent fungal strains and fermentation processes are essential for the efficient production of MELs, so efforts have been made to improve the fermentation yield by screening high-yielding strains, optimizing fermentation conditions, and improving product purification processes. The availability of the genome sequence is pivotal for elucidating the genetic basis of fungal MEL biosynthesis. This review aims to shed light on the applications of MELs and provide insights into the genetic basis for efficient MEL production. Additionally, this review offers new perspectives on optimizing MEL production, contributing to the advancement of sustainable biosurfactant technologies.

Rhamnolipid Self-Aggregation in Aqueous Media: A Long Journey toward the Definition of Structure–Property Relationships

The need to protect human and environmental health and avoid the widespread use of substances obtained from nonrenewable sources is steering research toward the discovery and development of new molecules characterized by high biocompatibility and biodegradability. Due to their very widespread use, a class of substances for which this need is particularly urgent is that of surfactants. In this respect, an attractive and promising alternative to commonly used synthetic surfactants is represented by so-called biosurfactants, amphiphiles naturally derived from microorganisms. One of the best-known families of biosurfactants is that of rhamnolipids, which are glycolipids with a headgroup formed by one or two rhamnose units. Great scientific and technological effort has been devoted to optimization of their production processes, as well as their physicochemical characterization. However, a conclusive structure–function relationship is far from being defined. In this review, we aim to move a step forward in this direction, by presenting a comprehensive and unified discussion of physicochemical properties of rhamnolipids as a function of solution conditions and rhamnolipid structure. We also discuss still unresolved issues that deserve further investigation in the future, to allow the replacement of conventional surfactants with rhamnolipids.

Development and optimization of amphiphilic self-assembly into nanostructured liquid crystals for transdermal delivery of an antidiabetic SGLT2 inhibitor

The anti-hyperglycemic sodium glucose co-transporter 2 inhibitor Canagliflozin (CFZ) represents a recent antihyperglycemic modality, yet it suffers from low oral bioavailability. The current work aims to formulate CFZ-loaded transdermal nanostructured liquid crystal gel matrix (NLCG) to improve its therapeutic efficiency. Pre-formulation study included the construction of pseudoternary phase diagrams to explore the effect of two conventional amphiphiles against amphiphilic tri-block copolymer in the formulation of NLCG. The influence of different co-solvents was also investigated with the use of monooleine as the oil. Physical characterization, morphological examination and skin permeation were performed for the optimized formulations. The formula of choice was further investigated for skin irritation and chemical stability. Pharmacodynamic evaluation of the successful formula was conducted on hyperglycemic as well as normoglycemic mice. In addition, oral glucose tolerance test was conducted. Results revealed the supremacy of Poloxamer for stabilizing and maximizing liquid crystal gel (LCG) area percentage that reached up to 12.6%. CFZ-NLCG2 isotropic formula showed the highest permeation parameters; maximum flux value of 7460 μg/cm² h and Q₂₄ of 5327 μg/cm². Pharmacodynamic evaluation revealed the superiority of the antihyperglycemic activity of CFZ-NLCG2 in fasting mice and its equivalence in the oral glucose tolerance test (OGTT) compared to the oral one. The obtained results confirmed the success of CFZ-NLCG2 in the transdermal delivery of CFZ in therapeutically effective concentration compared to the oral route, bypassing first pass effect; in addition, eliminates the possible gastrointestinal side effects related to the inhibition of intestinal sodium glucose co-transporter (SGLT) and maximizes its selectivity to the desired inhibition of renal SGLT.

Self-Assembled Structure of α-Isostearyl Glyceryl Ether Affects Skin Permeability-a Lamellar with 70-nm Spaces and L3 Phase Enhanced the Transdermal Delivery of a Hydrophilic Model Drug

Self-assembled surfactant structures, such as liquid crystals, have the potential to enhance transdermal drug delivery. In the present study, the pseudo-ternary system of GET (composed of α-Isostearyl glyceryl ether (GEIS) and polysorbate 60)/1,3 butanediol (BG)/water) was shown to exhibit a complex phase diagram. Small- and wide-angle X-ray scattering (SWAXS) and freeze-fracture transmission electron microscopy (FF-TEM) revealed that GET6BG60 (6%GET/60%BG/34%Water) formed a lamellar phase with a repeated distance of approximately 72 nm. Such a long-repeated distance of the lamellar phase was unique in the surfactant system. Moreover, the various structures, such as multilamellar vesicles and branched-like layers, were observed, which suggested that they might be deformable. On the other hand, only core-shell particles were observed in GET6BG20, the core of which was an L₃ phase. GET6BG20 and GET6BG60 significantly enhanced the skin permeation of the hydrophilic model drug, antipyrine (ANP) (log K_o/w, - 1.51). However, their permeation profiles were distinct. Liquid chromatography-tandem mass spectrometry revealed that epidermal accumulation of GEIS was significantly higher with GET6BG60 than GET6BG20 after 1.5 h of permeation, which might be attributed to differences in their deformable properties. Furthermore, GEIS was reported to affect intercellular lipids. Accumulated GEIS in the epidermis may have interacted with intercellular lipids and enhanced the transdermal delivery of ANP. The difference in the permeation profiles of ANP may be attributed to the penetration process of GEIS in the epidermis. This study suggests that GET6BG20 and GET6BG60 are unique carriers to enhance the permeation of hydrophilic drugs, such as ANP.

Lyotropic Liquid-Crystalline Phases of Sophorolipid Biosurfactants

Biological amphiphiles derived from natural resources are presently being investigated in the hope that they will someday replace current synthetic surfactants, which are known pollutants of soils and water resources. Sophorolipids constitute one of the main classes of glycosylated biosurfactants that have attracted interest because they are synthesized by non-pathogenic yeasts from glucose and vegetable oils at high titers. In this work, the self-assembly properties of several sophorolipids in water at high concentrations (20-80 wt %), a range so far mostly uncharted, have been investigated by polarized-light microscopy and X-ray scattering. Some of these compounds were found to show lyotropic liquid-crystalline behavior as they display lamellar or hexagonal columnar mesophases. X-ray scattering data shows that the structure of the lamellar phase is almost fully interdigitated, which is likely due to the packing difference between the bulky hydrophilic tails and the more compact aliphatic chains. A tentative representation of the molecular organization of the columnar phase is also given. Moreover, some of these compounds display thermotropic liquid-crystalline behavior, either pure or in aqueous mixtures. In addition, small domains of the lamellar phase can easily be aligned by applying onto them a moderate a.c. electric field, which is a rather unusual feature for lyotropic liquid crystals. Altogether, our work explored the self-assembly liquid-crystalline behavior of sophorolipids at high concentration, which could shed light on the conditions of their potential industrial applications as well as on their biological function.

Roles of mannosylerythritol lipid-B components in antimicrobial activity against bovine mastitis-causing Staphylococcus aureus

Mannosylerythritol lipid-B (MEL-B), which comprises ester-bonded hydrophilic ME and hydrophobic fatty acids, is a bio-surfactant with various unique properties, including antimicrobial activity against most gram-positive bacteria. The gram-positive Staphylococcus aureus is a causative pathogen of dairy cattle mastitis, which results in considerable economic loss in the dairy industry. Here, we demonstrate the efficacy of MEL-B as a disinfectant against bovine-derived S. aureus and elucidate a mechanism of action of MEL-B in the inhibition of bacterial growth. The growth of bovine mastitis causative S. aureus BM1006 was inhibited when cultured with MEL-B above 10 ppm. The activity of MEL-B required fatty acids (i.e., caprylic and myristoleic acids) as ME, the component of MEL-B lacking fatty acids, did not inhibit the growth of S. aureus even at high concentrations. Importantly, ME-bound fatty acids effectively inhibited the growth of S. aureus when compared with free fatty acids. Specifically, the concentrations of ME-bound fatty acids and free caprylic and myristoleic acids required to inhibit the growth of S. aureus were 10, 1442, and 226 ppm, respectively. The involvement of ME in the antimicrobial activity of MEL-B was confirmed by digestion of MEL-B with alkali, which dissociated ME and fatty acids. These results indicated that a mechanism of action of MEL-B in inhibiting the growth of S. aureus could be explained by the effective transporting of antimicrobial fatty acids to the bacterial surface via hydrophilic ME.

Phase Behaviour, Functionality, and Physicochemical Characteristics of Glycolipid Surfactants of Microbial Origin

Growing demand for biosurfactants as environmentally friendly counterparts of chemically derived surfactants enhances the extensive search for surface-active compounds of biological (microbial) origin. The understanding of the physicochemical properties of biosurfactants such as surface tension reduction, dispersion, emulsifying, foaming or micelle formation is essential for the successful application of biosurfactants in many branches of industry. Glycolipids, which belong to the class of low molecular weight surfactants are currently gaining a lot of interest for industrial applications. For this reason, we focus mainly on this class of biosurfactants with particular emphasis on rhamnolipids and sophorolipids, the most studied of the glycolipids.

Glycolipid Biosurfactants, Mannosylerythritol Lipids: Distinctive Interfacial Properties and Applications in Cosmetic and Personal Care Products

Biosurfactants produced by a variety of microorganisms show attractive properties (e.g., higher surface activity and biodegradability, lower toxicity, and environmental compatibility) compared to chemically synthesized counterparts. The numerous advantages of biosurfactants have prompted their application to not only the food, cosmetic, and pharmaceutical industries, but agriculture and environmental protection disciplines as well. Among different types of biosurfactants, glycolipids are the most practically useful, due to their high product titers from renewable resources and versatile interfacial and biochemical properties. Mannosylerythritol lipids (MELs) are characteristic glycolipid biosurfactants that are produced by different yeast strains of the genus Pseudozyma. MELs exhibit different lyotropic liquid crystalline phases, such as sponge (L₃), reverse bicontinuous cubic (V₂), or lamellar (L_α) phases; and they have high levels of surface activity at very low concentrations. MELs also show excellent moisturizing effects on human skin and hair, with comparable performance to natural ceramides. Today, MELs are commercially produced by a Japanese company and their use is rapidly expanding around the world. In this review, we will briefly describe the current R&D status of glycolipid biosurfactants, with a focus on the interfacial properties of MELs and their applications in cosmetic and personal care products.

Self-Assembling Properties and Recovery Effects on Damaged Skin Cells of Chemically Synthesized Mannosylerythritol Lipids

Mannosylerythritol lipids (MELs), which are one of the representative sugar-based biosurfactants (BSs) produced by microorganisms, have attracted much attention in various fields in the sustainable development goals (SDGs) era. However, they are inseparable mixtures with respect to the chain length of the fatty acids. In this study, self-assembling properties and structure-activity relationship (SAR) studies of recovery effects on damaged skin cells using chemically synthesized MELs were investigated. It was revealed, for the first time, that synthetic and homogeneous MELs exhibited significant self-assembling properties to form droplets or giant vesicles. In addition, a small difference in the length of the fatty acid chains of the MELs significantly affected their recovery effects on the damaged skin cells. MELs with medium or longer length alkyl chains exhibited much higher recovery effects than that of C18-ceramide NP.

Surface Properties and Liquid Crystal Properties of Alkyltetra(oxyethyl) β-d-Glucopyranoside

Hydrophilic alkyl polyglycosides (APGs) and alkyl glycosides (AGs) with anomeric pure are a class of important substitutes for petroleum-based surfactants. Improving their water solubility should make such hydrophilic glycosurfactants have more excellent potential application value. To solve the inherent problem of poor water solubility of traditional alkyl β-d-glucopyranoside (5), a series of alkyltetra(oxyethyl) β-d-glucopyranosides (4a-4g, n = 7-18) were successfully synthesized by introducing tetra(oxyethylene) fragments to carry out the structural modification. The relationship between the related structure and the physicochemical properties was further investigated, including their hydrophilic-lipophilic balance (HLB), water-solubility, foaming performance, emulsification, hygroscopicity, surface activity, and thermotropic/lyotropic liquid crystal phase behavior. The results showed that the water solubility gradually decreased as the alkyl chain length increased due to the gradual decrease of their HLB number. Octadecyltetra(oxyethyl) β-d-glucopyranoside (4g, n = 18) was found to be insoluble in water at 25 °C. Taken together, long-chain alkyl glycosides had good foaming properties and excellent emulsifying properties. Among them, dodecyltetra(oxyethyl) β-d-glucopyranoside (4d, n = 12) had the best foaming performance. In the rapeseed oil/water system, cetyltetra(oxyethyl) β-d-glucopyranoside (4f, n = 16) had the best emulsifying ability. With the increase of the alkyl chain length, the critical micelle concentration (C_cmc), γ_cmc, Γ_max, and hygroscopicity of this series of glycosides showed a downward trend. Differential scanning calorimetry (DSC) and polarizing optical microscopy (POM) showed that the thermal stability increased with the increase of the alkyl chain length, and alkyltetra(oxyethyl) β-d-glucopyranosides (4d-4g, n = 12-18) had the corresponding melting points and clearing points. Alkyltetra(oxyethyl) β-d-glucopyranosides (4b-4g, n = 8-18) formed a smectic phase with a typical fan-shaped and focal conic texture during the cooling process. In the water contact experiments, it was found that glycosides (4b-4g, n = 8-18) at high concentrations transformed into various lyotropic liquid crystal including hexagonal phase, bicontinuous cubic phase, and lamellar phase phases. Therefore, such green nonionic glycosurfactants alkyltetra(oxyethyl) β-d-glucopyranosides should have potential practical application prospects.

Congener-dependent conformations of isolated rhamnolipids at the vacuum-water interface: A molecular dynamics simulation

HYPOTHESIS

Molecular dynamics simulation can be used to differentiate between the adsorption properties of rhamnolipid congeners at a vacuum-water interface.

EXPERIMENTS

Adsorption of five congeners with differing alkyl chains (two C10 chains, two C14 chains or mixed C14C10 and C10C14), number of rhamnose rings (mono- or di-) and carboxyl group charge (non-ionic or anionic) are simulated at the vacuum-water interface.

FINDINGS

All rhamnolipids adsorb in the interfacial region with rhamnose and carboxyl groups closer to the water phase, and alkyl chains closer to the vacuum phase, but with differing adsorbed conformations. Headgroups of uncharged congeners show two preferred conformations, closed and partially open. Di-rhamnolipid has a low proportion of closed conformation, due to the steric constraints of the second pyranose ring. Charged congeners show strong preference for closed headgroup conformations. For rhamnolipids with equal alkyl chains lengths (C10C10, C14C14) the distribution of alkyl chain tilt angles is similar for both. Where chain lengths are unequal (C14C10, C10C14) one chain has a greater tendency to tilt towards the water phase (>90°). The order parameter of the alkyl chains shows they are disordered at the interface. Together, these results show congener-dependent adsorbed conformation differences suggesting they will have differing surface-active properties at vacuum-water and oil-water interfaces.

Cubic Liquid Crystals of Polyoxometalate-Based Ionic Liquids

Thermotropic ionic liquid crystals of polyoxometalate (POM)-based ionic liquids (POM-based ILs), which are formed by a POM, K₇PW₁₁O₃₉, and cationic surfactants, tetra-n-alkylammonium bromide ((C_nH_2n+1)₄N⁺Br^-, n = 6 and 7), are first proposed. As a model system, the cubic phase structure of a POM-based IL, {(C₇H₁₅)₄N⁺}₇PW₁₁O₃₉, was determined to form in a wide range of temperatures, exhibiting good thermostability, excellent mechanical strength, and high viscosity. Furthermore, the lyotropic ionic liquid crystals formed by {(C₇H₁₅)₄N⁺}₇PW₁₁O₃₉ in solvents such as chloroform or toluene still maintained a cubic structure. These cubic ionic liquid crystals (CILCs) were used as anticorrosion coatings both in acidic and neutral environments. The electrochemical measurements of Cu and Fe surfaces coated by CILCs showed an excellent ability of anticorrosion, indicating that the metals can be perfectly protected by the CILC coatings with high resistance and low capacitance. We assume that the CILCs may serve as barriers to stop oxygen diffusing to metals and interrupt the electron tunnels between the metal surfaces and the electrolyte solutions. Such environmentally friendly CILCs of POMs-based ILs are convenient for coating and removal, being vital to versatile industrial and academic applications.

Mannosylerythritol Lipid B Enhances the Skin Permeability of the Water-Soluble Compound Calcein via OH Stretching Vibration Changes

We confirmed that mannosylerythritol lipid B (MEL-B), a biosurfactant, enhances the skin permeability of the model water-soluble compound calcein. MEL-B liposomes were prepared by the thin-layer evaporation technique, and then applied to the skin. Although we attempted to adjust the size by extrusion, we could not control the particle diameter of the liposomes. However, the MEL-B liposome particle diameter remained the same over the 7-day study period. We observed an endothermic peak, with 74.7 °C as the transition temperature by differential scanning calorimetry. We also performed a fusion experiment with a fluorescence resonance energy transfer. A high amount of fusion of intercellular lipid liposomes and MEL-B liposomes occurred in a short period of time. After applying the MEL-B liposomes containing calcein to the skin, we measured the degree of calcein permeation and the amount of calcein within the skin. The resulting values were higher than those of an aqueous solution. The results obtained using a confocal laser scanning microscope suggested that calcein had been delivered deeply into the skin. Using the attenuation of total reflectance Fourier-transform infrared spectrometry, we observed that the OH stretching vibration had shifted to a higher wavenumber; however, this did not affect the CH stretching vibration. The measurement of transepidermal water loss after four days of continuous application of 1% MEL-B to animals revealed no changes. Our results suggest that MEL-B increases the skin permeability of compounds (calcein) that are difficult to deliver transdermally by changing the OH stretching vibration, which shifts to a higher wavenumber.

Mannosylerythritol lipids: antimicrobial and biomedical properties

Mannosylerythritol lipids (MELs) have attracted particular interest of medical, pharmaceutical, and cosmetic fields, due to their specific characteristics, including non-toxicity, easy biodegradability, and environmental compatibility. Therefore, this review aims to highlight recent findings on MEL biological properties, focusing on issues related to therapeutic applications. Among the main findings is that MELs can play a fundamental role due to their antimicrobial properties against several nosocomial pathogen microorganisms. Other remarkable biological properties of MELs are related to skincare, as antiaging (active agent), and in particular on recover of skin cells that were damaged by UV radiation. MEL is also related to the increased efficiency of DNA transfection in liposome systems. Regarding the health field, these glycolipids seem to be associated with disturbance in the membrane composition of cancerous cells, increasing expression of genes responsible for cytoplasmic stress and apoptosis. Moreover, MELs can be associated with nanoparticles, as a capping agent, also acting to increase the solubility and cytotoxicity of them. Furthermore, the differences in the chemical structure of MEL could improve and expand their biochemical diversity and applications. Such modifications could change their interfacial properties and, thus, reduce the surface tension value, enhance the solubility, lower critical micelle concentrations, and form unique self-assembly structures. The latest is closely related to molecular recognition and protein stabilization properties of MEL, that is, essential parameters for their effective cosmetical and pharmaceutical effects. Thus, this current research indicates the huge potential of MEL for use in biomedical formulations, either alone or in combination with other molecules.

Targeted transcriptomic study of the implication of central metabolic pathways in mannosylerythritol lipids biosynthesis in Pseudozyma antarctica T-34

Pseudozyma antarctica is a nonpathogenic phyllosphere yeast known as an excellent producer of industrial lipases and mannosylerythritol lipids (MELs), which are multi-functional glycolipids. The fungus produces a much higher amount of MELs from vegetable oil than from glucose, whereas its close relative, Ustilago maydis UM521, produces a lower amount of MELs from vegetable oil. In the present study, we used previous gene expression profiles measured by DNA microarray analyses after culturing on two carbon sources, glucose and soybean oil, to further characterize MEL biosynthesis in P. antarctica T-34. A total of 264 genes were found with induction ratios and expression intensities under oily conditions with similar tendencies to those of MEL cluster genes. Of these, 93 were categorized as metabolic genes using the Eukaryotic Orthologous Groups classification. Within this metabolic category, amino acids, carbohydrates, inorganic ions, and secondary metabolite metabolism, as well as energy production and conversion, but not lipid metabolism, were enriched. Furthermore, genes involved in central metabolic pathways, such as glycolysis and the tricarboxylic acid cycle, were highly induced in P. antarctica T-34 under oily conditions, whereas they were suppressed in U. maydis UM521. These results suggest that the central metabolism of P. antarctica T-34 under oily conditions contributes to its excellent oil utilization and extracellular glycolipid production.

On the Molecular Interactions in Lipid Bilayer-Water Assemblies of Different Curvatures

This work concerns the importance of intermolecular interactions present in aqueous lipid assembly systems depending on the type of aggregates they form. We have studied aqueous mixtures of diglycerol monooleate, Capmul glycerol monoleate (GMO-50) and polyoxyethylene (20) sorbitan monooleate (Polysorbate 80, P80) using small-angle X-ray scattering (SAXS) measurements to reveal the structure of liquid crystalline phases. On the basis of the SAXS data, a phase diagram was constructed. We discuss the effect of curvature changes of the lipid-aqueous interface obtained by changing the water content and the temperature. The results are related to the intermolecular interactions, as revealed by Raman spectroscopy, with a focus on the bilayer type of system of different curvature and bilayer flexibility, namely, the lamellar phase, bicontinuous cubic phase, and sponge phase. All phases show large similarities in their chain conformation and head group interactions as revealed by the Raman spectra, arising from the fact that all three structures are formed by lipid bilayers. However, subtle differences in the molecular organization of the sponge phase were revealed by employing Raman difference spectroscopy and by analysis of key spectroscopic indicators, which show a less dense hydrocarbon chain packing compared to the inverse bicontinuous cubic or lamellar phase.

Self-assembling Properties of an N-Heterocyclic Carbene-based Metallosurfactant: Pd-Coordination Induced Formation of Reactive Interfaces in Water

In this study, an N-heterocyclic carbene (NHC)-based metallosurfactant (MS), NHC-PdMS, was synthesized, where Pd(II) was bound to the NHC framework via a robust Pd-carbene bond with NEt₃ as a co-ligand. Surface tension measurements revealed that the critical micelle concentration (CMC) of NHC-PdMS (1.8×10^-4 M) was one order of magnitude lower than that of its MS precursor (imidazolium bromide). Coordination of the MS precursor and NEt₃ to Pd(II) also influenced micelle size; the hydrodynamic diameters of NHC-PdMS and the MS precursor were observed to be 25.8±5.6 nm and 2.5±0.3 nm, respectively. Furthermore, small angle X-ray scattering measurements indicated that NHC-PdMS exhibited liquid crystalline behavior above 26 wt%, with a spacing ratio of 1:2:3 for the first, second, and third Bragg peaks. To understand the role of the reactive interface, NHC-PdMS was also applied to aqueous catalytic reactions. Owing to its low CMC value, a catalytic amount of NHC-PdMS (3 mol%) provided the reactive interface, which facilitated the aqueous Mizoroki-Heck reaction of various aryl iodides and styrene in good yields (72-95%). These results suggest that MS formation results in a drastic change in selfassembling properties, which are important for the development of highly reactive chemical interfaces in water.

Anhydrous octyl-glucoside phase transition from lamellar to isotropic induced by electric and magnetic fields

A static deuterium nuclear magnetic resonance (²HNMR) technique (magnetic field, B = 7.05 T) was employed to monitor the thermotropic lamellar phase of the anhydrous 1:1 mixture sample of octyl-b-D-glucoside (βOG) and that of partially deuterium labelled at the alpha position on the chain, i.e.,βOG-d₂ In the absence of an electric field, the ²H NMR spectrum of the mixture gives a typical quadrupolar doublet representing the aligned lamellar phase. Upon heating to beyond the clearing temperature at 112 °C, this splitting converts to a single line expected for an isotropic phase. Simultaneous application of magnetic and electric fields (E = 0.4 MV/m) at 85 °C in the lamellar phase, whose direction was set to be parallel or perpendicular to the magnetic field, resulted in the change of the doublet into a single line and this recovers to the initial doublet with time for both experimental geometries. This implies E- and B-field-induced phase transitions from the lamellar to an isotropic phase and a recovery to the lamellar phase again with time. Moreover, these phase transformations are accompanied by a transient current. A similar observation was made in a computational study when an electric field was applied to a water cluster system. Increasing the field strength distorts the water cluster and weakens its hydrogen bonds leading to a structural breakdown beyond a threshold field-strength. Therefore, we suggest the observed field-induced transition is likely due to a structure change of the βOG lamellar assembly caused by the field effect and not due to Joule heating.

Biosurfactant-Protein Interaction: Influences of Mannosylerythritol Lipids-A on β-Glucosidase

In this work, the influences of a biosurfactant, mannosylerythritol lipids-A (MEL-A) toward β-glucosidase activity and their molecular interactions were studied by using differential scanning calorimetry (DSC), circular dichroism spectroscopy (CD), isothermal titration calorimetry (ITC), and docking simulation. The enzyme inhibition kinetics data showed that MEL-A at a low concentration (< critical micelle concentration (CMC), 20.0 ± 5.0 μM) enhanced β-glucosidase activity, whereas it inhibited the enzyme activity at higher concentrations more than 20.0 μM, followed by a decreased V_max and K_m of β-glucosidase. The thermodynamics and structural data demonstrated that the midpoint temperature (T_m) and unfolding enthalpy (ΔH) of β-glucosidase was shifted to high values (76.6 °C, 126.3 J/g) in the presence of MEL-A, and the secondary structure changes of β-glucosidase, including the increased α-helix, β-turn, or random coil contents, and a decreased β-sheet content were caused by MEL-A at a CMC concentration. The further ITC and docking simulations suggested the bindings of MEL-A toward β-glucosidase were driven by weak hydrophobic interactions happened between the amino acid residues of β-glucosidase and the fatty acid residues of MEL-A, in addition to hydrogen bonds between amino acids and hydroxyl in glycosyl residues of this biosurfactant.

Chemically Stable Lipids for Membrane Protein Crystallization

Lipidic cubic phase (LCP) has been widely recognized as a promising membrane-mimicking matrix for biophysical studies of membrane proteins and their crystallization in a lipidic environment. Application of this material to a wide variety of membrane proteins, however, is hindered due to a limited number of available host lipids, mostly monoacylglycerols (MAGs). Here, we designed, synthesized and characterized a series of chemically stable lipids resistant to hydrolysis, with properties complementary to the widely used MAGs. In order to assess their potential to serve as host lipids for crystallization, we characterized the phase properties and lattice parameters of mesophases made of two most promising lipids at a variety of different conditions by polarized light microscopy and small-angle X-ray scattering. Both lipids showed remarkable chemical stability and an extended LCP region in the phase diagram covering a wide range of temperatures down to 4 °C. One of these lipids has been used for crystallization and structure determination of a prototypical membrane protein bacteriorhodopsin at 4 °C and 20 °C.

Current status in biotechnological production and applications of glycolipid biosurfactants

Biosurfactants are natural compounds with surface activity and emulsifying properties produced by several types of microorganisms and have been considered an interesting alternative to synthetic surfactants. Glycolipids are promising biosurfactants, due to low toxicity, biodegradability, and chemical stability in different conditions and also because they have many biological activities, allowing wide applications in different fields. In this review, we addressed general information about families of glycolipids, rhamnolipids, sophorolipids, mannosylerythritol lipids, and trehalose lipids, describing their chemical and surface characteristics, recent studies using alternative substrates, and new strategies to improve of production, beyond their specificities. We focus in providing recent developments and trends in biotechnological process and medical and industrial applications.

Swelling of Bicontinuous Cubic Phases in Guerbet Glycolipid: Effects of Additives

Inverse bicontinuous cubic phases of lyotropic liquid crystal self-assembly have received much attention in biomedical, biosensing, and nanotechnology applications. An Ia3d bicontinuous cubic based on the gyroid G-surface can be formed by the Guerbet synthetic glucolipid 2-hexyl-decyl-β-d-glucopyranoside (β-Glc-OC6C10) in excess water. The small water channel diameter of this cubic phase could provide nanoscale constraints in encapsulation of large molecules and crystallization of membrane proteins, hence stresses the importance of water channel tuning ability. This work investigates the swelling behavior of lyotropic self-assembly of β-Glc-OC6C10 which could be controlled and modulated by different surfactants as a hydration-modulating agent. Our results demonstrate that addition of nonionic glycolipid octyl-β-d-glucopyranoside (β-Glc-OC8) at 20 and 25 mol % gives the largest attainable cubic water channel diameter of ca. 62 Å, and formation of coacervates which may be attributed to a sponge phase were seen at 20 mol % octyl-β-d-maltopyranoside (β-Mal-OC8). Swelling of the cubic water channel can also be attained in charged surfactant-doped systems dioctyl sodium sulfosuccinate (AOT) and hexadecyltrimethylammonium bromide (CTAB), of which phase transition occurred from cubic to a lamellar phase. Destabilization of the cubic phase to an inverse hexagonal phase was observed when a high amount of charged lecithin (LEC) and stearylamine (SA) was added to the lipid self-assembly.

Characterization and Inducing Melanoma Cell Apoptosis Activity of Mannosylerythritol Lipids-A Produced from Pseudozyma aphidis

Mannosylerythritol lipids (MELs) are natural glycolipid biosurfactants which have potential applications in the fields of food, cosmetic and medicine. In this study, MELs were produced from vegetable oil by Pseudozyma aphidis. Their structural data through LC/MS, GC/MS and NMR analysis revealed that MEL-A with two acetyls was the major compound and the identified homologs of MEL-A contained a length of C8 to C14 fatty acid chains. This glycolipid exhibited a surface tension of 27.69 mN/m at a critical micelle concentration (CMC), self-assembling into particles in the water solution. It was observed to induce cell growth-inhibition and apoptosis of B16 melanoma cells in a dose-dependent manner, as well as cause cell cycle arrest at the S phase. Further quantitative RT-PCR analysis and western blotting revealed an increasing tendency of both mRNA and protein expressions of Caspase-12, CHOP, GRP78 and Caspase-3, and a down-regulation of protein Bcl-2. Combined with the up regulation of signaling IRE1 and ATF6, it can be speculated that MEL-A-induced B16 melanoma cell apoptosis was associated with the endoplasmic reticulum stress (ERS).

Characteristics of mannosylerythritol lipids and their environmental potential

Mannosylerythritol lipids (MELs) are promising biosurfactants containing two glycosyl derivatives and various fatty acids, which are mainly secreted by Pseudozyma as well as Ustilago. In this review, the latest research is demonstrated on production conditions, structural diversity, self-assembling properties and versatile biochemical functions of MELs. The genetic study and synthetic pathways, which mainly influence the type and yield of MELs production. Due to the excellent surface activity, biocompatibility and restorative function, MELs can be used in enviornmental industry, which has not been widely noted. In this paper, the current status of research on enviornmental potential of MELs has been discussed including petroleum degradation, bioconversion of chemical wastes and enhanced bioremediation of amphiphilic wastes.

Aqueous gel formation from sodium salts of cellobiose lipids

Cellobiose lipids (CLs) are asymmetric bolaform biosurfactants, which are produced by Cryptococcus humicola JCM 10251 and have fungicidal activity. In this study, the sodium salts of CLs (CLNa) were prepared to improve aqueous solubility of the CLs, and their surface and gelation properties in aqueous solutions were examined by surface tension, rheology, and freeze-fracture transmission electron microscopy (FF-TEM) measurements. The surface tension measurements revealed that the CLNa have high surface activity: CMC1 and γCMC1 are 0.1 mg/mL and 34.7 mN/m, respectively. It was also found that the CLNa form giant micelles above their CMC, whose average size is 116.6 ± 31.9 nm. Unlike conventional surfactants, the surface tension reduced further with an increase in concentration and the aqueous solution became viscous at the minimum gelation concentration (MGC: 5.0 mg/mL). In rheological studies, the obtained gels proved to be rather soft and their sol-gel temperature was found to be approximately 50℃. FF-TEM observation of the gels showed 3D supramolecular structures with an entangled fibrous network. Since the present CLNa aqueous gels have a degree of fungicidal activity, they could be useful for novel multifunctional soft materials applicable to the food and cosmetic industries.

Production and identification of mannosylerythritol lipid-A homologs from the ustilaginomycetous yeast Pseudozyma aphidis ZJUDM34

Mannosylerythritol lipids (MELs) are mainly produced by strains of the genus Pseudozyma and by Ustilago maydis. These glycolipid biosurfactants exhibit not only excellent surface-active properties but also versatile bioactivities. Mannosylerythritol lipid-A (MEL-A) is worth investigating due to its self-assembling property. In this work, crude MELs were produced by resting Pseudozyma aphidis ZJUDM34 cells using different culture media. MEL-A fractions were isolated and identified using high-performance liquid chromatography combined with mass spectrometry (HPLC-MS) and gas chromatography combined with mass spectrometry (GC-MS). The results showed that MEL-A homologs had long unsaturated fatty acid chains, and the chain lengths range from C8 to C20. Nuclear magnetic resonance (NMR) was employed to confirm the chemical structures of the MEL-A homologs. Fermentation medium without NaNO3 and medium with manganese ions enhanced MEL-A production by Pseudozyma aphidis ZJUDM34.

Biosurfactant-producing yeasts widely inhabit various vegetables and fruits

The isolation of biosurfactant-producing yeasts from food materials was accomplished. By a combination of a new drop collapse method and thin-layer chromatography, 48 strains were selected as glycolipid biosurfactant producers from 347 strains, which were randomly isolated from various vegetables and fruits. Of the producers, 69% were obtained from vegetables of the Brassica family. Of the 48 producers, 15 strains gave relatively high yields of mannosylerythritol lipids (MELs), and were identified as Pseudozyma yeasts. These strains produced MELs from olive oil at yields ranging from 8.5 to 24.3 g/L. The best yield coefficient reached 0.49 g/g as to the carbon sources added. Accordingly, MEL producers were isolated at high efficiency from various vegetables and fruits, indicating that biosurfactant producers are widely present in foods. The present results should facilitate their application in the food and related industries.

Genome and transcriptome analysis of the basidiomycetous yeast Pseudozyma antarctica producing extracellular glycolipids, mannosylerythritol lipids

Pseudozyma antarctica is a non-pathogenic phyllosphere yeast known as an excellent producer of mannosylerythritol lipids (MELs), multi-functional extracellular glycolipids, from vegetable oils. To clarify the genetic characteristics of P. antarctica, we analyzed the 18 Mb genome of P. antarctica T-34. On the basis of KOG analysis, the number of genes (219 genes) categorized into lipid transport and metabolism classification in P. antarctica was one and a half times larger than that of yeast Saccharomyces cerevisiae (140 genes). The gene encoding an ATP/citrate lyase (ACL) related to acetyl-CoA synthesis conserved in oleaginous strains was found in P. antarctica genome: the single ACL gene possesses the four domains identical to that of the human gene, whereas the other oleaginous ascomycetous species have the two genes covering the four domains. P. antarctica genome exhibited a remarkable degree of synteny to U. maydis genome, however, the comparison of the gene expression profiles under the culture on the two carbon sources, glucose and soybean oil, by the DNA microarray method revealed that transcriptomes between the two species were significantly different. In P. antarctica, expression of the gene sets relating fatty acid metabolism were markedly up-regulated under the oily conditions compared with glucose. Additionally, MEL biosynthesis cluster of P. antarctica was highly expressed regardless of the carbon source as compared to U. maydis. These results strongly indicate that P. antarctica has an oleaginous nature which is relevant to its non-pathogenic and MEL-overproducing characteristics. The analysis and dataset contribute to stimulate the development of improved strains with customized properties for high yield production of functional bio-based materials.

Coacervation of cationic gemini surfactant with N-benzoylglutamic acid in aqueous solution

Coacervation of cationic gemini surfactant hexamethylene-1,6-bis(dodecyldimethylammonium bromide) (12-6-12) with pH-sensitive N-benzoylglutamic acid (H2Bzglu) has been investigated by potentiometric pH-titration, turbidity titration, dynamic light scattering (DLS), isothermal titration calorimetry (ITC), TEM, (1)H NMR, and light microscopy. Phase boundaries of the 12-6-12/H2Bzglu mixture were obtained over the pH range from 2 to 9 and in the H2Bzglu concentration range from 30.0 to 50.0 mM at pH 4.5. When the H2Bzglu concentration is beyond 30.0 mM, the 12-6-12/H2Bzglu mixed solution undergoes the phase transitions from soluble aggregate, to precipitate, coacervate, and soluble aggregate again as pH increases. The results indicate that coacervation occurs at extremely low 12-6-12 concentration and lasts over a wide surfactant range, and can be enhanced or suppressed by changing pH, 12-6-12/H2Bzglu molar ratio and H2Bzglu concentration. The coacervates present a disorderly connected lay structure. Coacervation only takes place at pH 4-5, where the aggregates are nearly charge neutralized, and a minimum H2Bzglu concentration of 30.0 mM is required for coacervation. In this pH range, H2Bzglu mainly exist as HBzglu(-). The investigations on intermolecular interactions indicate that the aggregation of 12-6-12 is greatly promoted by the strong electrostatic and hydrophobic interactions with the HBzglu(-) molecules, and the interaction also promotes the formation of dimers, trimers, and tetramers of HBzglu(-) through hydrogen bonds. The double chains of 12-6-12 and the HBzglu(-) oligomers can play the bridging roles connecting aggregates. These factors endow the mixed system with a very high efficiency in generating coacervation.

Self-assembly of squalene-based nucleolipids: relating the chemical structure of the bioconjugates to the architecture of the nanoparticles

Squalene-based nucleolipids, including anticancer or antiviral prodrugs, gave rise to nanoparticles displaying a diversity of structures upon nanoprecipitation in water. Synchrotron small-angle X-ray scattering and cryo-TEM imaging revealed that both the nature of the nucleoside and the position of the squalene moiety relative to the nucleobase determined the self-assembly of the corresponding bioconjugates. It was found that small chemical differences resulted in major differences in the self-organization of nucleolipids when squalene was grafted onto the nucleobase whereas only lamellar phases were observed when squalene was linked to the sugar moiety. The key role of hydrogen bonds between nucleobases in the formation of the lamellar phases was suggested, in agreement with molecular simulations. These findings provide a way to fine tune the supramolecular organization of squalene-based prodrugs, with the aim of improving their pharmacological activity.

Production of mannosylerythritol lipids and their application in cosmetics

Mannosylerythritol lipids (MELs) are glycolipid biosurfactants abundantly produced by different basidiomycetous yeasts such as Pseudozyma, and show not only excellent interfacial properties but also versatile biochemical actions. These features of MELs make their application in new technology areas possible. Recently, the structural and functional variety of MELs was considerably expanded by advanced microbial screening methods. Different types of MELs bearing different hydrophilic and hydrophobic parts have been reported. The genes responsible for MEL biosynthesis were identified, and their genetic study is now in progress, aiming to control the chemical structure. The excellent properties leading to practical cosmetic ingredients, i.e., moisturization of dry skin, repair of damaged hair, activation of fibroblast and papilla cells and antioxidant and protective effects in skin cells, have been demonstrated on the yeast glycolipid biosurfactants. In this review, the current status of research and development on MELs, particularly the commercial application in cosmetics, is described.

Genome Sequence of the Basidiomycetous Yeast Pseudozyma antarctica T-34, a Producer of the Glycolipid Biosurfactants Mannosylerythritol Lipids

The basidiomycetous yeast Pseudozyma antarctica T-34 is an excellent producer of mannosylerythritol lipids (MELs), members of the multifunctional extracellular glycolipids, from various feedstocks. Here, the genome sequence of P. antarctica T-34 was determined and annotated. Analysis of the sequence might provide insights into the properties of this yeast that make it superior for use in the production of functional glycolipids, leading to the further development of P. antarctica for industrial applications.

Production and characterization of a glycolipid biosurfactant, mannosylerythritol lipid B, from sugarcane juice by Ustilago scitaminea NBRC 32730

Mannosylerythritol lipids (MELs) are glycolipid biosurfactants excreted by fungal strains. They show not only excellent surface-active properties but also versatile biochemical actions. Ustilago scitaminea NBRC 32730 has been reported mainly to produce a mono-acetylated and di-acylated MEL, MEL-B, from sucrose as sole carbon source. In order to make biosurfactant production more efficient, we focused our attention on the use of sugarcane juice, one of the most economical resources. The fungal strain produced MEL-B at the yield of 12.7 g/L from only sugarcane juice containing 22.4% w/w sugars. Supplementation with organic (yeast extract, peptone, and urea) and inorganic (sodium nitrate and ammonium nitrate) nitrogen sources markedly enhanced the production yield. Of the nitrogen sources, urea gave the best yield. Under optimum conditions, the strain produced 25.1 g/L of MEL-B from the juice (19.3% sugars) supplemented with 1 g/L of urea in a jar fermenter at 25 °C over 7 d. The critical micelle concentration (CMC) and the surface-tension at the CMC for the present MEL-B were 3.7×10(-6) M and 25.2 mN/m respectively. On water-penetration scan, the biosurfactant efficiently formed the lamella phase (L(α)) and myelins over a wide range of concentrations, indicating excellent surface-active and self-assembling properties. More significantly, the biosurfactant showed a ceramide-like skin-care property in a three-dimensional cultured human skin model. Thus, sugarcane juice is likely to be effective in glycolipid production by U. scitaminea NBRC 32730, and should facilitate the application of MELs.

Isolation of Pseudozyma churashimaensis sp. nov., a novel ustilaginomycetous yeast species as a producer of glycolipid biosurfactants, mannosylerythritol lipids

An ustilaginomycetous anamorphic yeast species isolated from the leaves of Saccharum officinarum (sugarcane) in Okinawa, Japan, was identified as a novel Pseudozyma species based on morphological and physiological aspects and molecular taxonomic analysis using the D1/D2 domains of the large subunit (26S) rRNA gene and the internal transcribed spacer 1 (ITS1)-5.8S-ITS2 regions. The name Pseudozyma churashimaensis sp. nov. was proposed for the novel species, with JCM 16988(T) as the type strain. Interestingly, P. churashimaensis was found to produce glycolipid biosurfactants, a mixture of mannosylerythritol lipids (MELs), including a novel tri-acetylated derivative (MEL-A2), from glucose. The observed critical micelle concentration (CMC) and the surface tension at CMC of MEL-A2 were 1.7 × 10⁻⁶ M and 29.2 mN/m, respectively. Moreover, on a water-penetration scan, MEL-A2 efficiently formed different lyotropic liquid crystalline phases, including the lamella phase at a wide range of concentrations, indicating its excellent surface-active and self-assembling properties. The novel strain of the genus Pseudozyma should thus facilitate the application of glycolipid biosurfactants in combination with other MEL producers.

Identification of the gene PaEMT1 for biosynthesis of mannosylerythritol lipids in the basidiomycetous yeast Pseudozyma antarctica

The yeast Pseudozyma antarctica produces a large amount of glycolipid biosurfactants known as mannosylerythritol lipids (MELs), which show not only excellent surface-active properties but also versatile biochemical actions. To investigate the biosynthesis of MELs in the yeast, we recently reported expressed sequence tag (EST) analysis and estimated genes expressing under MEL production conditions. Among the genes, a contiguous sequence of 938 bp, PA_004, showed high sequence identity to the gene emt1, encoding an erythritol/mannose transferase of Ustilago maydis, which is essential for MEL biosynthesis. The predicted translation product of the extended PA_004 containing the two introns and a stop codon was aligned with Emt1 of U. maydis. The predicted amino acid sequence shared high identity (72%) with Emt1 of U. maydis, although the amino-terminal was incomplete. To identify the gene as PaEMT1 encoding an erythritol/mannose transferase of P. antarctica, the gene-disrupted strain was developed by the method for targeted gene disruption, using hygromycin B resistance as the selection marker. The obtained ΔPaEMT1 strain failed to produce MELs, while its growth was the same as that of the parental strain. The additional mannosylerythritol into culture allowed ΔPaEMT1 strain to form MELs regardless of the carbon source supplied, indicating a defect of the erythritol/mannose transferase activity. Furthermore, we found that MEL formation is associated with the morphology and low-temperature tolerance of the yeast.