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Sophorolipids production by the yeast Candia bombicola is most favourable when glucose is used as a carbon source in combination with a hydrophobic carbon source such as a common vegetable oil. Most vegetable oils are comprised of C16-C18 fatty acids, an ideal range for sophorolipid production. The use of oils with either shorter or longer fatty acids, such has coconut oil or meadowfoam oil, respectively, was evaluated. Such oils did not contribute to enhanced sophorolipid production when compared to cultures run on glucose as the sole carbon source. Moreover, a toxic effect of medium-chain fatty acids towards stationary C. bombicola cells was demonstrated. [ABSTRACT FROM AUTHOR]

Antimicrobial peptides (AMPs) are considered promising candidates to treat various infections in soft tissues and skin. However, no effective treatment based on AMPs has been reached to clinics due to their instability in serum and wounds. Biosurfactants such as acidic sophorolipids (ASLs) of very high concentrations (equal or above 5 mg/mL) have been demonstrated to be antimicrobial agents, however these concentrations might induce cytotoxic effects to human cells. Here, we have demonstrated the synergistic antimicrobial effect of ASL nanoparticles (NPs) and LL37 peptides (below their minimum inhibitory concentrations; MICs) to eradicate Gram-positive and Gram-negative bacteria in human serum (HS) and in the presence of trypsin. The formulations containing ASL NPs (500 μg/mL) and LL37 peptides (15-25 μg/mL) effectively kill wide strains of bacteria in 5 % HS and the presence of trypsin. Moreover, the combination of ASL NPs (500 μg/mL) and LL37 peptides (15 μg/mL) prevents the formation of S. aureus biofilm and eradicates the one-day old biofilm. Importantly, the combination of ASL NPs and LL37 peptides severely damages the cell membrane of Escherichia coli (E. coli) as shown by atomic force microscopy (AFM). The combination of ASL NPs and LL37 peptides rapidly damages the outer (OM) and inner membrane (IM) of E. coli, while ASL NPs (1000 μg/mL) alone slowly compromise the integrity of the bacterial membrane. Importantly, the combination of ASL NPs and LL37 peptides is biocompatible to human keratinocyte cells (HaCaTs) and human umbilical vein endothelial cells (HUVECs), and induces the expression of anti-inflammatory cytokine in macrophages. Overall, ASL NPs in combination with LL37 peptides might be developed as an effective topical formulation to prevent bacterial infections in the skin., Competing Interests: Declaration of competing interest Authors declare no conflict of interest that could influence the work reported in this manuscript., (Copyright © 2023 Elsevier B.V. All rights reserved.)

The United Nations' Sustainable Development Goals have sparked growing interest in biosurfactants from many surfactant-loaded industries including those utilizing froth flotation for mineral separation. However, the interaction of biosurfactants with mineral surfaces is currently poorly understood. We bridge this gap by studying adsorption of a yeast-derived bola acidic sophorolipid (ASL) biosurfactant on djurleite (Cu 1.94 S). The methods used include Hallimond flotation, contact angle, adsorption isotherm, zeta potential, leaching measurements, and X-ray photoelectron spectroscopy (XPS). To facilitate the interpretation of the adsorption results, we characterize the activity of ASL at the air-water interface and measure its critical micelle concentration (CMC) at different pH using static surface tension. We find ASL to be a multifunctional surfactant with an unusual, pH-sensitive interfacial behavior. At the air-water interface, ASL is most active at pH 8, while its CMC goes through minimum as low as 40 μM at pH 7. The surfactant adsorption at the djurleite-water interface makes the sulfide surface hydrophilic at acidic pH and hydrophobic at neutral and basic pH. In addition, ASL has strong affinity to copper sulfide and demonstrates metal leaching properties. Finally, ASL demonstrates detergency properties. We offer a mechanistic interpretation of these findings. Our results provide a basis for the application of acidic glycolipids in froth flotation and have implications for their application in ion separation using hydrometallurgical routes, as well as for the chemical stability of metal sulfides in environmental systems., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 The Authors. Published by Elsevier Inc. All rights reserved.)

The demand for microbially produced surface-active compounds for use in industrial processes and products is increasing. As such, there has been a comparable increase in the number of publications relating to the characterization of novel surface-active compounds: novel producers of already characterized surface-active compounds and production processes for the generation of these compounds. Leading researchers in the field have identified that many of these studies utilize techniques are not precise and accurate enough, so some published conclusions might not be justified. Such studies lacking robust experimental evidence generated by validated techniques and standard operating procedures are detrimental to the field of microbially produced surface-active compound research. In this publication, we have critically reviewed a wide range of techniques utilized in the characterization of surface-active compounds from microbial sources: identification of surface-active compound producing microorganisms and functional testing of resultant surface-active compounds. We have also reviewed the experimental evidence required for process development to take these compounds out of the laboratory and into industrial application. We devised this review as a guide to both researchers and the peer-reviewed process to improve the stringency of future studies and publications within this field of science., (© 2020 The Authors. Microbial Biotechnology published by Society for Applied Microbiology and John Wiley & Sons Ltd.)

Vesicle-in-vesicle self-assembled containers, or vesosomes, are promising alternatives to liposomes because of their possible hierarchical encapsulation and high stability. We report herein the first example of sugar-based vesicles-in-vesicles, which we baptize glucosomes. These were prepared by using a natural microbial glycolipid (branched C22 sophorolipid) extracted from the culture medium of the yeast Pseudohyphozyma bogoriensis . Glucosomes spontaneously formed in water between pH 6 and pH 4 at room temperature, without the requirement of any additive. By means of pH-resolved in situ small angle X-ray scattering, we provided direct evidence for the vesicle-formation mechanism. Statistical treatment of the vesicle radii distribution measured by cryo-tansmission electron microscopy by using a derived form of the Helfrich bending free-energy expression provided an order of magnitude for the effective bending constant (the sum of the curvature and the saddle-splay moduli) of the lipid membrane to K= (0.4±0.1)  k B T . This value is in agreement with the bending constant measured for hydrocarbon-based vesicles membranes.

Sophorolipids (SLs), a class of microbially derived biosurfactants, are reported by different research groups to have different self-assembled structures (either micelles or giant ribbons) under the same conditions. Here we explore the reasons behind these contradictory results and attribute these differences to the role of specific congeners that are present in minute quantities. We show that a sample composed of a majority of oleic acid (C18:1) sophorolipid in the presence of only 0.5 % (or more) of congeners with stearic acid (C18:0) or linoleic acid (C18:2) results in the formation of micelles that are stable over long periods of time. Conversely, the presence of only 10 to 15 % of congeners with a stearic acid chain gives fibrillar structures instead of micelles. To study the mechanisms responsible, oleic acid SLs devoid of any other congeners were prepared. Very interestingly, this sample can self-assemble into either micelles or fibers depending on minute modifications to the self-assembly conditions. The findings are supported by light scattering, small-angle X-ray scattering, transmission electron microscopy under cryogenic conditions, high-pressure liquid chromatography, and NMR spectroscopy., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Biosurfactants are of growing interest as sustainable alternatives to fossil-fuel-derived chemical surfactants, particularly for the detergent industry. To realize this potential, it is necessary to understand how they affect proteins which they may encounter in their applications. However, knowledge of such interactions is limited. Here, we present a study of the interactions between the model protein apo-α-lactalbumin (apo-aLA) and the biosurfactant sophorolipid (SL) produced by the yeast Starmerella bombicola . SL occurs both as an acidic and a lactonic form; the lactonic form (lactSL) is sparingly soluble and has a lower critical micelle concentration (cmc) than the acidic form [non-acetylated acidic sophorolipid (acidSL)]. We show that acidSL affects apo-aLA in a similar way to the related glycolipid biosurfactant rhamnolipid (RL), with the important difference that RL is also active below the cmc in contrast to acidSL. Using isothermal titration calorimetry data, we show that acidSL has weak and saturable interactions with apo-aLA at low concentrations; due to the relatively low cmc of acidSL (which means that the monomer concentration is limited to ca. 0-1 mM SL), it is only possible to observe interactions with monomeric acidSL at high apo-aLA concentrations. However, the denaturation kinetics of apo-aLA in the presence of acidSL are consistent with a collaboration between monomeric and micellar surfactant species, similar to RL and non-ionic or zwitterionic surfactants. Inclusion of diacetylated lactonic sophorolipid (lactSL) as mixed micelles with acidSL lowers the cmc and this effectively reduces the rate of unfolding, emphasizing that SL like other biosurfactants is a gentle anionic surfactant. Our data highlight the potential of these biosurfactants for future use in the detergent and pharmaceutical industry.

A set of four structurally related glycolipids are described: two of them have one glucose unit connected to either stearic or oleic acid, and two other ones have a diglucose headgroup (sophorose) similarly connected to either stearic or oleic acid. The self-assembly properties of these compounds, poorly known, are important to know due to their use in various fields of application from cleaning to cosmetics to medical. At basic pH, they all form mainly small micellar aggregates. At acidic pH, the oleic and stearic derivatives of the monoglucose form, respectively, vesicles and bilayer, while the same derivatives of the sophorose headgroup form micelles and twisted ribbons. We use pH-resolved in situ small angle X-ray scattering (SAXS) under synchrotron radiation to characterize the pH-dependent mechanism of evolution from micelles to the more complex aggregates at acidic pH. By pointing out the importance of the COO - /COOH ratio, the melting temperature, T m , of the lipid moieties, hydration of the glycosidic headgroup, the packing parameter, membrane rigidity, and edge stabilization, we are now able to draw a precise picture of the full self-assembly mechanism. This work is a didactical illustration of the complexity of the self-assembly process of a stimuli-responsive amphiphile during which many concomitant parameters play a key role at different stages of the process.

Microbial glycolipids are a class of well-known compounds, but their self-assembly behavior is still not well understood. While the free carboxylic acid end group makes some of them interesting stimuli-responsive compounds, the sugar hydrophilic group and the nature of the fatty acid chain make the understanding of their self-assembly behavior in water not easy and highly unpredictable. Using cryo-transmission electron microscopy (cryo-TEM) and both pH-dependent in situ and ex situ small angle X-ray scattering (SAXS), we demonstrate that the aqueous self-assembly at room temperature (RT) of a family of β-d-glucose microbial glycolipids bearing a saturated and monounsaturated C18 fatty acid chain cannot be explained on the simple basis of the well-known packing parameter. Using the "pH-jump" process, we find that the molecules bearing a monosaturated fatty acid forms vesicles below pH 6.2, as expected, but the derivative with a saturated fatty acid forms infinite bilayer sheets below pH 7.8, instead of vesicles. We show that this behavior can be explained on the different bilayer membrane elasticity as a function of temperature. Membranes are either flexible or stiff for experiments performed at a temperature respectively above or below the typical melting point, TM, of the lipidic part of each compound. Finally, we also show that the disaccharide-containing acidic cellobioselipid forms a majority of chiral fibers, instead of the expected micelles.