Biological activity of mannosylerythritol lipids on the mammalian cells

Mannosylerythritol lipids (MEL) are glycolipids mainly produced by pseudo-yeasts. These molecules present remarkable biological activities widely explored in many fields, including medicine, pharmaceuticals, and cosmetics. This review presents the main biological activity of MEL on the HL60, K562, B16, PC12, and skin cells. There is strong evidence that MEL changes the levels of glycosphingolipids of HL-60 lineage, which induce differentiation into granulocytic cells. Regarding B16 cells, MEL can trigger both apoptosis (10 μM) and cell differentiation (5 μM), in which the MEL concentration is related to each metabolic pathway. MEL can also trigger differentiation in PC12 cells due to the increase in the GalCer content. In this specific case, the effects are transient, and the differentiated cells are unstable and tend to apoptosis. MEL-B can particularly maintain skin hydration and moisture due to their self-assembled structures that resemble the tissue cells. Moreover, MEL-B repair aquaporin expression in the HaCaT keratinocytes damaged with UVA irradiation, whereas MEL-C suppresses the expression of COX-2 protein in fibroblasts, indicating that these glycolipids activate the cellular antioxidant mechanism. Recent findings denoted the anti-melanogenic activity of MEL since they suppress tyrosinase enzyme at mRNA levels in B16 and NHMs cells. MEL act effectively on mammalian cells; however, there is no clear pattern of their metabolic effects. Also, gene expression levels seem to be related to two main factors: chemical structure and concentration. However, the specific signaling cascades that are induced by MEL remain inconclusive. Thus, further investigations are vital to understanding these mechanisms clearly. KEY POINTS: • The four MEL homologs promote different biological responses in mammalian cells. • MEL modifies the pattern of glycosphingolipids in the plasma membrane of tumor cells. • Activation/deactivation of phosphorylation of serine/threonine kinase proteins.

Identification and importance of mitochondrial citrate carriers and ATP citrate lyase for glycolipid production in Starmerella bombicola

Starmerella bombicola is a non-conventional yeast commercially used as a microbial cell factory for sophorolipid production. Sophorolipids are glycolipid biosurfactants composed of a glucose disaccharide sophorose and a fatty acid. In de novo sophorolipid synthesis, the fatty acid moiety is derived from the fatty acid synthesis (FAS) complex; therefore, the yeast's lipid metabolism plays a crucial role in sophorolipid biosynthesis. As a fatty acid precursor, citric acid is a key primary metabolite that connects carbohydrate and lipid metabolism, and in S. bombicola, it also has a regulatory effect on sophorolipid composition and productivity. We aimed to identify the mitochondrial transporters involved in citrate shuttling and the ATP citrate lyase (Acl), the enzyme that converts citric acid into acetyl-CoA. Subsequently, we studied their role in the citric acid shuttle and glycolipid synthesis and the potential of citrate metabolism as a genetic manipulation target for increased glycolipid synthesis. Bioinformatics analyses predicted 32 mitochondrial carriers of which two were identified as citrate transporters, named SbCtp1 and SbYhm2. Deletion of these mitochondrial carriers led to a lesser sophorolipid yield and a shift in the lactonic/acidic sophorolipid ratio. However, only the knockout of SbYhm2 caused a decrease of citric and an increase of malic acid extracellular concentrations. Additionally, deletion of SbAcl1 had a negative effect on S. bombicola's specific growth rate and sophorolipid synthesis and contributed to extra- and intracellular citric acid accumulation. Unexpectedly, SbAcl1 overexpression also decreased glycolipid production.Key Points• Starmerella bombicola is an industrially relevant microbial cell factory for biosurfactant production.• There are 32 predicted mitochondrial carriers in S. bombicola.• Citrate mitochondrial carriers SbYhm2 and SbCtp1 are essential for glycolipid synthesis in S. bombicola.• Deletion of SbAcl1 negatively affects growth and sophorolipid production in S. bombicola. Graphical abstract.

Effects of sophorolipids on fungal and oomycete pathogens in relation to pH solubility

AIMS

The objective of this study was to determine the effects of sophorolipids on several fungal and oomycete plant pathogens and the relationship between sophorolipids at different pH and antimicrobial activities.

METHODS AND RESULTS

Sophorolipids had different solubility at different pH with a dramatic increase in solubility when pH was 6 or higher. Inhibition of mycelial growth of Phytophthora infestans by sophorolipids was affected by pH values, showing that when the pH value was higher, the inhibition rate was lower. Sophorolipids inhibited spore germination and mycelial growth of several fungal and oomycete pathogens in vitro including Fusarium sp., F. oxysporum, F. concentricum, Pythium ultimum, Pyricularia oryzae, Rhizoctorzia solani, Alternaria kikuchiana, Gaeumannomyces graminis var. tritici and P. infestans and caused morphological changes in hyphae by microscope observation. Sophorolipids reduced β-1,3-glucanase activity in mycelia of P. infestans. In greenhouse studies, foliar application of sophorolipids at 3 mg ml^-1 reduced severity of late blight of potato caused by P. infestans significantly.

CONCLUSION

Sophorolipids influenced spore germination and hyphal tip growth of several plant pathogens and pH solubility of sophorolipids had an effect on their efficacy. Application of sophorolipids reduced late blight disease on potato under greenhouse conditions.

SIGNIFICANCE AND IMPACT OF THE STUDY

The findings indicated that sophorolipids have the potential to be developed as a convenient and easy-to-use formulation for managing plant diseases.

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.

Redirecting the lipid metabolism of the yeast Starmerella bombicola from glycolipid to fatty acid production

Free fatty acids are basic oleochemicals implemented in a range of applications including surfactants, lubricants, paints, plastics, and cosmetics. Microbial fatty acid biosynthesis has gained much attention as it provides a sustainable alternative for petrol- and plant oil-derived chemicals. The yeast Starmerella bombicola is a microbial cell factory that naturally employs its powerful lipid metabolism for the production of the biodetergents sophorolipids (> 300 g/L). However, in this study we exploit the lipidic potential of S. bombicola and convert it from the glycolipid production platform into a free fatty acid cell factory. We used several metabolic engineering strategies to promote extracellular fatty acid accumulation which include blocking competing pathways (sophorolipid biosynthesis and β-oxidation) and preventing free fatty acid activation. The best producing mutant (Δcyp52m1Δfaa1Δmfe2) secreted 0.933 g/L (± 0.04) free fatty acids with a majority of C18:1 (43.8%) followed by C18:0 and C16:0 (40.0 and 13.2%, respectively). Interestingly, deletion of SbFaa1 in a strain still producing sophorolipids also resulted in 25% increased de novo sophorolipid synthesis (P = 0.0089) and when oil was supplemented to the same strain, a 50% increase in sophorolipid production was observed compared to the wild type (P = 0.03). We believe that our work is pivotal for the further development and exploration of S. bombicola as a platform for synthesis of environmentally friendly oleochemicals.

Antiangiogenic activity of sophorolipids extracted from refined bleached deodorized palm olein

OBJECTIVES:

Sophorolipids (SLs) are a group of surface-active glycolipids produced by a type of nonpathogenic yeast Candida bombicola in the presence of vegetable oil through fermentation technology. SLs have shown antitumor activity; however, the mechanism of action underlying the anticancer activity of SLs is poorly understood. This work evaluated the anticancer activity of SLs fermented from palm oil by exploring its antiangiogenic activity.

MATERIALS AND METHODS:

The SLs that were fermented and further characterized for their biochemical activities. Cytotoxicity study was performed to assess cytostatic properties. A series of in vitro and ex vivo angiogenesis assay was also carried out. The relative fold change in the expression of p53 mRNA by SLs was also studied.

RESULTS:

Altogether, the data show that SLs derived from palm oil fermentation process inhibited neovascularization in the ex vivo tissue segments and also the endothelial cell proliferation between 50% and 65% inhibition as a whole. The palm oil derived SLs also caused downregulation of the suppression level of vascular endothelial growth factor and also upregulate the p53 mRNA level. The analytical studies revealed the presence of high amount of phenolic compounds but with relatively weak antioxidant activity. The gas chromatography-mass spectrometry studies revealed abundant amount of palmitic and oleic acid, the latter an established antiangiogenic agent, and the former being proangiogenic.

CONCLUSION:

Therefore, it can be concluded from this study that SLs derived from fermented palm oil have potent antiangiogenic activity which may be attributed by its oleic acid component.

Screening and isolation of the liamocin-producing yeast Aureobasidium melanogenum using xylose as the sole carbon source

Xylose, the main component of xylan, is the second most abundant sugar in nature after glucose. Consequently, xylose represents an attractive feedstock for the production of value-added compounds such as biosurfactants (BSs), which are produced by various bacteria and yeasts. In this study, we screened and isolated yeast strains that synthesize BSs using xylose as the sole carbon source. We applied matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) to screen for BS-producing yeasts and isolated eight strains as the liamocin producers. Two of the eight strains, AS37 and SK25, were identified as Aureobasidium melanogenum, which is known as black yeasts, by based on 26S ribosomal RNA gene sequences. Both strains produced a wide variety of liamocin structures from not only xylose but also glucose and sucrose. According to the MALDI-TOF MS analysis, signals corresponding to sodium ion adducts of di-, tri-, tetra-, penta- and hexa-acylated C6-liamocins and di-, tri- and tetra-acylated C5-liamocins were detected. In addition, their mono-acetylated form was also detected. The dominant sugar component of liamocins produced by strains AS37 and SK25 is mannitol as estimated by HPLC analysis. This is the first report to describe the screening of liamocins-producing yeasts using xylose as the sole carbon source.

Emulsion Formation and Stabilization by Biomolecules: The Leading Role of Cellulose

Emulsion stabilization by native cellulose has been mainly hampered because of its insolubility in water. Chemical modification is normally needed to obtain water-soluble cellulose derivatives. These modified celluloses have been widely used for a range of applications by the food, cosmetic, pharmaceutic, paint and construction industries. In most cases, the modified celluloses are used as rheology modifiers (thickeners) or as emulsifying agents. In the last decade, the structural features of cellulose have been revisited, with particular focus on its structural anisotropy (amphiphilicity) and the molecular interactions leading to its resistance to dissolution. The amphiphilic behavior of native cellulose is evidenced by its capacity to adsorb at the interface between oil and aqueous solvent solutions, thus being capable of stabilizing emulsions. In this overview, the fundamentals of emulsion formation and stabilization by biomolecules are briefly revisited before different aspects around the emerging role of cellulose as emulsion stabilizer are addressed in detail. Particular focus is given to systems stabilized by native cellulose, either molecularly-dissolved or not (Pickering-like effect).

Marine Biosurfactants: Biosynthesis, Structural Diversity and Biotechnological Applications

Biosurfactants are amphiphilic secondary metabolites produced by microorganisms. Marine bacteria have recently emerged as a rich source for these natural products which exhibit surface-active properties, making them useful for diverse applications such as detergents, wetting and foaming agents, solubilisers, emulsifiers and dispersants. Although precise structural data are often lacking, the already available information deduced from biochemical analyses and genome sequences of marine microbes indicates a high structural diversity including a broad spectrum of fatty acid derivatives, lipoamino acids, lipopeptides and glycolipids. This review aims to summarise biosyntheses and structures with an emphasis on low molecular weight biosurfactants produced by marine microorganisms and describes various biotechnological applications with special emphasis on their role in the bioremediation of oil-contaminated environments. Furthermore, novel exploitation strategies are suggested in an attempt to extend the existing biosurfactant portfolio.

Influence of microorganism and plant oils on the structure of mannosylerythritol lipid (MEL) biosurfactants revealed by a novel thin layer chromatography mass spectrometry method

Mannosylerythritol lipids (MEL) are microbial glycolipid biosurfactants with great potential for application in cosmetics and household detergents. In current biotechnological processes, they are produced by basidiomycetous fungi, the Ustilaginaceae, as a complex mixture of different chemical structures. It was the aim of this paper to study the influence of producer organisms and substrates on the resulting MEL structures with a novel high-resolution HPTLC-MALDI-TOF method. Given the seven different microbes and four plant oils, our analysis revealed that the product concentrations varied strongly between organisms, while they were similar for the different substrates. Coconut oil presented an exception, since only one organism was able to synthesize MEL from this substrate in considerable yields. Analysis by GC-FID further showed that the chain length pattern of hydrophobic fatty acid side-chains was very specific for individual organisms, while substrates had only a minor influence on the chain length. Our novel HPTLC-MALDI-TOF combination method finally demonstrated the presence of multiple MEL sub-variants with differing acetylation and fatty acid chain lengths. It also revealed the production of a more hydrophilic biosurfactant mannosylmannitol lipid (MML) as a side-product in certain fungi. Overall, it was concluded that the pattern of produced biosurfactant structures are mainly governed by producer organisms rather than substrates.