Structural analysis of fungal cerebrosides

Identification and structural characterization of glucosylceramides in Holothuria (Halodeima) grisea: Insights from TLC and NMR techniques

Sea cucumbers are widely used in oriental cuisine due to their medicinal properties. Antioxidant, antifungal, antiviral, anticancer and neuroprotective activities have already been identified in several species and in different tissues. Among the class of compounds with biological activity are cerebrosides, which have important functions for the proper functioning of cells, especially neuronal cells. The identification of this class of compounds can be carried out using simple techniques such as thin layer chromatography (TLC) or more sophisticated techniques such as nuclear magnetic resonance (NMR), providing different information depending on the technique used. Therefore, this work aimed to identify the presence of cerebrosides in different tissues of Holothuria (Halodeima) grisea. TLC analysis and separation on a silica column made it possible to accurately identify the positive fractions for cerebrosides. This selectivity is crucial to ensure that the compounds identified are genuine cerebrosides, eliminating interference from other non-pertinent bands. NMR spectroscopy analyses confirmed the presence of glucosylceramide in the tissues studied. The identification of a β-glucose linked to the ceramide, with specific structural characteristics such as hydroxyl on the 3' carbon of the sphingosine and a double bond between the 4' and 5' carbons, highlights the accuracy of the structural determination obtained with the techniques used.

The antimicrobial activity of ETD151 defensin is dictated by the presence of glycosphingolipids in the targeted organisms

Fungal infections represent a significant global health concern, with a growing prevalence of antifungal drug resistance. Targeting glucosylceramides (GlcCer), which are functionally important glycosphingolipids (GSL) present in fungal membranes, represents a promising strategy for the development of antifungal drugs. GlcCer are associated with the antifungal activity of certain plant and insect defensins. The 44-residue ETD151 peptide, optimized from butterfly defensins, is active against several fungal pathogens. ETD151 has been shown to induce a multifaceted mechanism of action (MOA) in Botrytis cinerea, a multiresistant phytopathogenic fungus. However, the target has yet to be identified. Our findings demonstrate that the presence of GlcCer in membranes determines the susceptibility of Pichia pastoris and Candida albicans toward ETD151. To ascertain whether this is due to direct molecular recognition, we demonstrate that ETD151 selectively recognizes liposomes containing GlcCer from B. cinerea, which reveals a methylated-sphingoid base structure. The dissociation constant was estimated by microscale thermophoresis to be in the µM range. Finally, fluorescence microscopy revealed that ETD151 localizes preferentially at the surface of B. cinerea. Furthermore, the majority of prokaryotic cells do not contain GSL, which explains their resistance to ETD151. We investigated the susceptibility of Novosphingobium capsulatum, one of the rare GSL-containing bacteria, to ETD151. ETD151 demonstrated transient morphological changes and inhibitory growth activity (IC50 ~75 µM) with an affinity for the cell surface, emphasizing the critical importance of GSL as target. Understanding the MOA of ETD151 could pave the way for new perspectives in human health and crop protection.

Screening for the production of polyunsaturated fatty acids and cerebrosides in fungi

AIMS

To investigate fatty acid, including polyunsaturated fatty acids (PUFA), and cerebroside production of a large diversity of fungi from the Ascomycota, Basidiomycota, and Mucoromycota phyla.

METHODS AND RESULTS

Seventy-nine fungal strains were grown in Kavadia medium using a microcultivation system, i.e. Duetz microtiter plates. Following cultivation, fatty acid and cerebroside contents were analyzed by gas chromatography-flame ionization detection (GC-FID) and high performance thin-layer chromatography (HPTLC), respectively. Mucoromycota fungi appeared as the most promising candidates for omega-6 PUFA production. The best omega-6 producer, including γ-linolenic acid (GLA, 18:3n-6), was Mucor fragilis UBOCC-A109196 with a concentration of 647 mg L-1 total omega-6 PUFA (representing 35% of total fatty acids) and 225 mg L-1 GLA (representing 12% of total fatty acids). Arachidonic acid concentration (20:4n-6) was the highest in Mortierella alpina UBOCC-A-112046, reaching 255 mg L-1 and 18.56% of total fatty acids. Interestingly, several fungal strains were shown to produce omega-7 monounsaturated fatty acids. Indeed, Torulaspora delbrueckii strains accumulated palmitoleic acid (16:1n-7) up to 20% of total fatty acids, reaching 114 mg L-1 in T. delbrueckii UBOCC-A-214128, while C. elegans UBOCC-A-102008 produced mainly paullinic acid (20:1n-7) with concentrations up to 100 mg L-1. Concerning cerebroside production, HPTLC appeared as a relevant approach for their detection and quantification. Promising candidates belonging to the Mucoromycota phylum were found, especially in the Absidia genus with A. spinosa UBOCC-A-101332 as the best producer (12.7 mg L-1).

CONCLUSIONS

The present study highlighted PUFA and cerebroside production in a large diversity of fungi and the fact that members of the Mucoromycota phylum are good producers of PUFA as well as cerebrosides.

Secondary Metabolites of Biscogniauxia: Distribution, Chemical Diversity, Bioactivity, and Implications of the Occurrence

The genus Biscogniauxia, a member of the family Xylariaceae, is distributed worldwide with more than 50 recognized taxa. Biscogniauxia species is known as a plant pathogen, typically acting as a parasite on tree bark, although certain members of this genus also function as endophytic microorganisms. Biscogniauxia endophytic strain has received attention in many cases, which includes constituent research leading to the discovery of various bioactive secondary metabolites. Currently, there are a total of 115 chemical compounds belonging to the class of secondary metabolites, and among these compounds, fatty acids have been identified. In addition, the strong pharmacological agents of this genus are (3aS,4aR,8aS,9aR)-3a-hydroxy-8a-methyl-3,5-dimethylenedecahydronaphto [2,3-b]furan-2(3H)-one (HDFO) (antifungal), biscopyran (phytotoxic activity), reticulol (antioxidant), biscogniazaphilone A and B (antimycobacterial), and biscogniauxone (Enzyme GSK3 inhibitor). This comprehensive research contributes significantly to the potential discovery of novel drugs produced by Biscogniauxia and holds promise for future development. Importantly, it represents the first-ever review of natural products originating from the Biscogniauxia genus.

Beyond membrane components: uncovering the intriguing world of fungal sphingolipid synthesis and regulation

Sphingolipids (SLs) are essential to fungal survival and represent a major class of structural and signaling lipids. Unique SL structures and their biosynthetic enzymes in filamentous fungi make them an ideal drug target. Several studies have contributed towards the functional characterization of specific SL metabolism genes, which have been complemented by advanced lipidomics methods which allow accurate identification and quantification of lipid structures and pathway mapping. These studies have provided a better understanding of SL biosynthesis, degradation and regulation networks in filamentous fungi, which are discussed and elaborated here.

Regulation mechanism of lipids for extracellular yellow pigments production by Monascus purpureus BWY-5

The biosynthesis and secretion of Monascus pigments are closely related to the integrity of the cell membrane, which determines the composition of lipids and its content in cell membrane. The present study aimed to thoroughly describe the changes of lipid profiling in Monascus purpureus BWY-5, which was screened by carbon ion beam irradiation (¹²C⁶⁺) to almost single yield extracellular Monascus yellow pigments (extra-MYPs), by absolute quantitative lipidomics and tandem mass tags (TMT) based quantitative proteomic. ¹²C⁶⁺ irradiation caused non-lipid oxidation damage to Monascus cell membrane, leading to an imbalance in cell membrane lipid homeostasis. This imbalance was attributed to significant changes not only in the composition but also in the content of lipids in Monascus, especially the inhibition of glycerophospholipid biosynthesis. Integrity of plasma membrane was maintained by the increased production of ergosterol, monogalactosylmonoacylglycerol (MGMG) and sulfoquinovosylmonoacylglycerol (SQMG), while mitochondrial membrane homeostasis was maintained by the increase of cardiolipin production. The growth and extra-MYPs production of Monascus BWY-5 have been regulated by the promotion of sphingolipids (ceramide and sulfatide) biosynthesis. Simultaneous, energy homeostasis may be achieved by increase of TG synthesis and Ca²⁺/Mg²⁺-ATPase activity. These finding suggest ergosterol, cardiolipin, sphingolipids, MGMG and SQMG play a key facilitating role in cytomembrane lipid homeostasis maintaining for Monascus purpureus BWY-5, and then it is closely related to cell growth and extra-MYPs production. KEY POINTS: 1. Energy homeostasis in Monascus purpureus BWY-5 was achieved by increase of TG synthesis and Ca²⁺/Mg²⁺-ATPase activity. 2. Integrity of plasma membrane in Monascus purpureus BWY-5 was maintained by the increased production of ergosterol. 3. Mitochondrial membrane homeostasis in Monascus purpureus BWY-5 was maintaed by the increase of cardiolipin synthesis.

Glucosylceramides from Cladosporium and Their Roles in Fungi–Plant Interaction

Cladosporium species are widely distributed filamentous fungi. One of the most important species is C. herbarum, which is related to infections in a variety of plants and of concern in plantations. Fungal cerebrosides, such as glucosylceramide (GlcCer), have been described as playing important roles in fungal growth and pathogenesis, but GlcCer from C. herbarum has not been characterized so far. For this reason, the present study aimed to elucidate the chemical structure of GlcCer from C. herbarum and its role in the interaction with Passiflora edulis. Mass spectrometry characterization of purified GlcCer revealed two major molecular ions, m/z 760 and m/z 774, and it reacts with monoclonal anti-GlcCer antibodies and is exposed on the fungal surface. P. edulis treatment with GlcCer induced increased levels of superoxide as well as the expression of some genes related to plant defense, such as PR3, POD, LOX and PAL. GlcCer also enhanced growth parameters, such as plant height and root weight. All these results suggest that C. herbarum GlcCer can stimulate plant defense mechanisms, which could help plants to face fungal infections.

A Langmuir-Blodgett Study of the Interaction between Amphotericin B and Lipids of Histoplasma capsulatum

Histoplasma capsulatum is a dimorphic, thermal, and nutritional fungus. In the environment and at an average temperature of 28 °C, it develops as a mold that is composed of infecting particles. Once in the host or in cultures at 37 °C, it undergoes a transition into the parasitic form. In the present work, we performed chemical extraction and characterization using chromatography techniques of the associated lipid composition of the external surface of the cell wall of the mycelial phase of two isolates of the H. capsulatum: one clinical and one environmental. Several differences were evidenced in the fatty acids in the phospholipid composition. Surface pressure–area isotherms and compression module curves of the Amphotericin B and lipid extract monolayers, as well as (AmB)-lipid extract mixed monolayers were recorded. Results show a high affinity of AmB towards lipid extracts. The most stable monolayers were formed by AmB + environmental with a mass ratio of 1:3 and AmB + clinical with a mass ratio of 1:2. Knowledge of the AmB aggregation processes at a molecular level and the characterization of the lipid extracts allows the possibility to understand the interaction between the AmB and the lipid fractions of H. capsulatum.

Unveiling microbial preservation under hyperacidic and oxidizing conditions in the Oligocene Rio Tinto deposit

The preservation of biosignatures on Mars is largely associated with extensive deposits of clays formed under mild early Noachian conditions (> 3.9 Ga). They were followed by widespread precipitation of acidic sulfates considered adverse for biomolecule preservation. In this paper, an exhaustive mass spectrometry investigation of ferric subsurface materials in the Rio Tinto gossan deposit (~ 25 Ma) provides evidence of well-preserved molecular biosignatures under oxidative and acidic conditions. Time of flight secondary ion mass spectrometry (ToF–SIMS) analysis shows a direct association between physical-templating biological structures and molecular biosignatures. This relation implies that the quality of molecular preservation is exceptional and provides information on microbial life formerly operating in the shallow regions of the Rio Tinto subsurface. Consequently, low-pH oxidative environments on Mars could also record molecular information about ancient life in the same way as the Noachian clay-rich deposits.

Identification and analyses of the chemical composition of a naturally occurring albino mutant chanterelle

White chanterelles (Basidiomycota), lacking the orange pigments and apricot-like odour of typical chanterelles, were found recently in the Canadian provinces of Québec (QC) and Newfoundland & Labrador (NL). Our phylogenetic analyses confirmed the identification of all white chanterelles from NL and QC as Cantharellus enelensis; we name these forma acolodorus. We characterized carotenoid pigments, lipids, phenolics, and volatile compounds in these and related chanterelles. White mutants of C. enelensis lacked detectable β-carotene, confirmed to be the primary pigment of wild-type, golden-orange individuals, and could also be distinguished by their profiles of fatty acids and phenolic acids, and by the ketone and terpene composition of their volatiles. We detected single base substitutions in the phytoene desaturase (Al-1) and phytoene synthase (Al-2) genes of the white mutant, which are predicted to result in altered amino acids in their gene products and may be responsible for the loss of β-carotene synthesis in that form.

Miltefosine Against Scedosporium and Lomentospora Species: Antifungal Activity and Its Effects on Fungal Cells

Scedosporium and Lomentospora species are filamentous fungi responsible for a wide range of infections in humans and are frequently associated with cystic fibrosis and immunocompromising conditions. Because they are usually resistant to many antifungal drugs available in clinical settings, studies of alternative targets in fungal cells and therapeutic approaches are necessary. In the present work, we evaluated the in vitro antifungal activity of miltefosine against Scedosporium and Lomentospora species and how this phospholipid analogue affects the fungal cell. Miltefosine inhibited different Scedosporium and Lomentospora species at 2–4 µg/ml and reduced biofilm formation. The loss of membrane integrity in Scedosporium aurantiacum caused by miltefosine was demonstrated by leakage of intracellular components and lipid raft disorganisation. The exogenous addition of glucosylceramide decreased the inhibitory activity of miltefosine. Reactive oxygen species production and mitochondrial activity were also affected by miltefosine, as well as the susceptibility to fluconazole, caspofungin and myoricin. The data obtained in the present study contribute to clarify the dynamics of the interaction between miltefosine and Scedosporium and Lomentospora cells, highlighting its potential use as new antifungal drug in the future.

Glycosphingolipids in Filamentous Fungi: Biological Roles and Potential Applications in Cosmetics and Health Foods

Filamentous fungi are a group of economically important fungi used in the production of fermented foods, industrial enzymes, and secondary metabolites. Glycosphingolipids (GSLs) as constituents of lipid rafts are involved in growth, differentiation, and response to environment stress in filamentous fungi. In addition to these key roles, GSLs are also important in the barrier function of skin to retain moisture as a moisturizing ingredient in cosmetics or health products for their strong biological activity as a functional component. GSLs found in filamentous fungi are divided in two major classes: neutral GSLs (glycosylceramides), glucosylceramides (GlcCers), and/or galactosylceramides (GalCers) and acidic GSLs, mannosylinositol phosphorylceramide (MIPC) and mannosyldiinositol phosphorylceramide [M(IP)₂C]. Glycosylceramides are one of the abundant GSLs in Aspergillus and known to improve skin-barrier function and prevent intestinal impairment as a prebiotic. Some filamentous fungi of Aspergillus spp., synthesizing both GlcCer and GalCer, would be an amenable source to exploit glycosylceramides that wildly adding in cosmetics as moisturizing ingredients or health food as dietary supplements. In this minireview, the types, structures, and biosynthetic pathways of GSLs in filamentous fungi, and the relevance of GSLs in fungal growth, spore formation, and environmental stress response are explained. Furthermore, the advantage, potential development, and application of GlcCer and GalCer from filamentous fungi Aspergillus spp. are also investigate based on the use of plant GlcCer in health foods and cosmetics.

Glycoglycerolipids from the leaves of Perilla frutescens (L.) Britton (Labiatae) and their anti-inflammatory activities in lipopolysaccharide-stimulated RAW264.7 cells

A described monogalactosyldiacylglycerol (MGDG) and two undescribed digalactosyldiacylglycerols (DGDGs) were isolated from the leaves of Perilla frutescens (L.) Britton (Labiatae) by using silica gel column chromatography and semi-preparative high performance liquid chromatography. The elucidation of complete structure of these compounds were conducted by using MS and NMR techniques. The MGDG (7.5% of total lipids) was identified as 1,2-2-O-(9Z,12Z,15E-octadecatrienoyl)-3-O-(β-D-galactopyranosyl)-sn-glycerol. The two DGDGs (2.8% and 1.0% of total lipids, respectively) were identified as 1-O-(9Z,12Z,15Z-octadecatrienoyl)-2-O-(6Z,9Z,12Z-octadecatrienoyl)-3-O-[β-D-galactopyranosyl-(1″→6')-α-D-galactopyranosyl]-sn-glycerol and 1-O- hexadecanoyl -2-O-(9Z,12Z,15Z-octadecatrienoy -l)-3-O-[β-D-galactopyranosyl-(1″→6')-α-D-galactopyranosyl]-sn-glycerol, respectively. All the isolated MGDG and DGDGs were evaluated for their anti-inflammatory activities in lipopolysaccharide (LPS)-stimulated murine macrophages RAW264.7 cells. All of them showed good inhibitory activities and significantly blocked the production of LPS-induced TNF-α, (IL)-1β and IL-6. The above results shed some light on a better understanding of the traditional anti-inflammatory effect of Perilla frutescens and reveal the potential anti-inflammatory constituents.

Glucosylceramide Plays a Role in Fungal Germination, Lipid Raft Organization and Biofilm Adhesion of the Pathogenic Fungus Scedosporium aurantiacum

Infections caused by Scedosporium species present a wide range of clinical manifestations, from superficial to disseminated, especially in immunocompromised patients. Glucosylceramides (GlcCer) are glycosphingolipids found on the fungal cell surface and play an important role in growth and pathogenicity processes in different fungi. The present study aimed to evaluate the structure of GlcCer and its role during growth in two S. aurantiacum isolates. Purified GlcCer from both isolates were obtained and its chemical structure identified by mass spectrometry. Using ELISA and immunofluorescence techniques it was observed that germination and NaOH-treatment of conidia favor GlcCer exposure. Monoclonal anti-GlcCer antibody reduced germination when cultivated with the inhibitor of melanin synthesis tricyclazole and also reduced germ tube length of conidia, both cultivated or not with tricyclazole. It was also demonstrated that anti-GlcCer altered lipid rafts organization, as shown by using the fluorescent stain filipin, but did not affect the susceptibility of the cell surface to damaging agents. Anti-GlcCer reduced total biomass and viability in biofilms formed on polystyrene plates. In the presence of anti-GlcCer, germinated S. aurantiacum conidia and biofilms could not adhere to polystyrene with the same efficacy as control cells. These results highlight the relevance of GlcCer in growth processes of S. aurantiacum.

Antiviral activity of glucosylceramides isolated from Fusarium oxysporum against Tobacco mosaic virus infection

Natural elicitors derived from pathogenic microorganisms represent an ecologic strategy to achieve resistance in plants against diseases. Glucosylceramides (GlcCer) are classified as neutral glycosphingolipids. GlcCer were isolated and purified from Fusarium oxysporum mycelium. F. oxysporum is a plant pathogenic fungus, abundant in soil and causing severe losses in economically important crops such as corn, tobacco, banana, cotton and passion fruit. In this study we evaluate the capacity of GlcCer in inducing resistance in N. tabacum cv Xanthi plants against Tobacco mosaic virus (TMV). Spraying tobacco plants with GlcCer before virus infection reduced the incidence of necrotic lesions caused by TMV. In addition, plants already infected with the virus showed a reduction in hypersensitive response (HR) lesions after GlcCer treatment, suggesting an antiviral effect of GlcCer. Our investigations showed that GlcCer stimulates the early accumulation of H2O2 and superoxide radicals. In addition, the expression of PR-1 (pathogenesis-related 1, with suggested antifungal action), PR-2 (β-1,3-glucanase), PR-3 (Chitinase), PR-5 (Osmotin), PAL (Phenylalanine ammonia-lyase), LOX (Lipoxygenase) and POX (Peroxidase) genes was highly induced after treatment of tobacco plants with GlcCer and induction levels remained high throughout a period of 6 to 120 hours. Our experiments demonstrate that GlcCer induces resistance in tobacco plants against infection by TMV.

Scedosporium Cell Wall: From Carbohydrate-Containing Structures to Host-Pathogen Interactions

Scedosporium species are filamentous fungi usually found in sewage and soil from human-impacted areas. They cause a wide range of diseases in humans, from superficial infections, such as mycetoma, to invasive and disseminated cases, especially associated in immunocompromised patients. Scedosporium species are also related to lung colonization in individuals presenting cystic fibrosis and are considered one of the most frequent fungal pathogens associated to this pathology. Scedosporium cell wall contains glycosylated molecules involved in important biological events related to virulence and pathogenicity and represents a significant source of antigens. Polysaccharides, peptidopolysaccharides, O-linked oligosaccharides and glycosphingolipids have been identified on the Scedosporium surface. Their primary structures were determined based on a combination of techniques including gas chromatography, ESI-MS, and ¹H and ¹³C nuclear magnetic resonance. Peptidorhamnnomannans are common cell wall components among Scedosporium species. Comparing different species, minor structural differences in the carbohydrate portions were detected which could be useful to understand variations in virulence observed among the species. N- and O-linked peptidorhamnomannans are major pathogen-associated molecular patterns and, along with α-glucans, play important roles in triggering host innate immunity. Glycosphingolipids, such as glucosylceramides, have highly conserved structures in Scedosporium species and are crucial for fungal growth and virulence. The present review presents current knowledge on structural and functional aspects of Scedosporium glycoconjugates that are relevant for understanding pathogenicity mechanisms and could contribute to the design of new agents capable of inhibiting growth and differentiation of Scedosporium species. Other cell components such as melanin and ectophosphatases will be also included.

Effects of Red-Bean Tempeh with Various Strains of Rhizopus on GABA Content and Cortisol Level in Zebrafish

Tempeh is traditionally produced by fermenting soybean with the fungus Rhizopus oligosporus found in banana leafs. We wanted to investigate if Taiwan's flavorful red bean could be used as a healthy substitute for soybeans in tempeh. One bioactive component of tempeh is γ-Aminobutyric acid (GABA). We measured GABA content and shelf-life-related antimicrobial activity in red-bean tempeh made with four strains of Rhizopus, one purchased strain of Rhizopus, and an experimental co-cultured group (Rhizopus and Lactobacillus rhamnosus BCRC16000) as well as cortisol in red-bean-tempeh-treated zebrafish. GABA was highest in the co-culture group (19.028 ± 1.831 g kg-1), followed by screened Strain 1, the purchased strain, and screened Strain 4. All strains had antibacterial activity on S. aureus and B. cereus. The extract significantly reduced cortisol in zebrafish. However, Strain 1, with less GABA than some of the other strains, had the best effect on cortisol level, suggesting that other components in red-bean tempeh may also affect stress-related cortisol. We found the benefits of red-bean tempeh to be similar to those reported for soybean-produced tempeh, suggesting that it could be produced as an alternative product. Considering the Taiwanese appreciation of the red-bean flavor, it might find a welcoming market.

Metabolomics and Machine Learning Approaches Combined in Pursuit for More Accurate Paracoccidioidomycosis Diagnoses

Brazil and many other Latin American countries are areas of endemicity for different neglected diseases, and the fungal infection paracoccidioidomycosis (PCM) is one of them. Among the clinical manifestations, pneumopathy associated with skin and mucosal lesions is the most frequent. PCM definitive diagnosis depends on yeast microscopic visualization and immunological tests, but both present ambiguous results and difficulty in differentiating PCM from other fungal infections. This research has employed metabolomics analysis through high-resolution mass spectrometry to identify PCM biomarkers in serum samples in order to improve diagnosis for this debilitating disease. To upgrade the biomarker selection, machine learning approaches, using Random Forest classifiers, were combined with metabolomics data analysis. The proposed combination of these two analytical methods resulted in the identification of a set of 19 PCM biomarkers that show accuracy of 97.1%, specificity of 100%, and sensitivity of 94.1%. The obtained results are promising and present great potential to improve PCM definitive diagnosis and adequate pharmacological treatment, reducing the incidence of PCM sequelae and resulting in a better quality of life.IMPORTANCE Paracoccidioidomycosis (PCM) is a fungal infection typically found in Latin American countries, especially in Brazil. The identification of this disease is based on techniques that may fail sometimes. Intending to improve PCM detection in patient samples, this study used the combination of two of the newest technologies, artificial intelligence and metabolomics. This combination allowed PCM detection, independently of disease form, through identification of a set of molecules present in patients' blood. The great difference in this research was the ability to detect disease with better confidence than the routine methods employed today. Another important point is that among the molecules, it was possible to identify some indicators of contamination and other infection that might worsen patients' condition. Thus, the present work shows a great potential to improve PCM diagnosis and even disease management, considering the possibility to identify concomitant harmful factors.

Structural Differences Influence Biological Properties of Glucosylceramides from Clinical and Environmental Isolates of Scedosporium aurantiacum and Pseudallescheria minutispora

Scedosporium/Lomentospora complex is composed of filamentous fungi, including some clinically relevant species, such as Pseudallescheria boydii, Scedosporium aurantiacum, and Scedosporium apiospermum. Glucosylceramide (GlcCer), a conserved neutral glycosphingolipid, has been described as an important cell surface molecule playing a role in fungal morphological transition and pathogenesis. The present work aimed at the evaluation of GlcCer structures in S. aurantiacum and Pseudallescheria minutispora, a clinical and an environmental isolate, respectively, in order to determine their participation in fungal growth and host-pathogen interactions. Structural analysis by positive ion-mode ESI-MS (electrospray ionization mass spectrometer) revealed the presence of different ceramide moieties in GlcCer in these species. Monoclonal antibodies against Aspergillus fumigatus GlcCer could recognize S. aurantiacum and P. minutispora conidia, suggesting a conserved epitope in fungal GlcCer. In addition, these antibodies reduced fungal viability, enhanced conidia phagocytosis by macrophages, and decreased fungal survival inside phagocytic cells. Purified GlcCer from both species led to macrophage activation, increasing cell viability as well as nitric oxide and superoxide production in different proportions between the two species. These results evidenced some important properties of GlcCer from species of the Scedosporium/Lomentospora complex, as well as the effects of monoclonal anti-GlcCer antibodies on fungal cells and host-pathogen interaction. The differences between the two species regarding the observed biological properties suggest that variation in GlcCer structures and strain origin could interfere in the role of GlcCer in host-pathogen interaction.

Lipidomic Profiling of the Olive (Olea europaea L.) Fruit towards Its Valorisation as a Functional Food: In-Depth Identification of Triacylglycerols and Polar Lipids in Portuguese Olives

Olives (Olea europaea L.) are classic ingredients in the Mediterranean diet with well-known health benefits, but their lipid composition has not been fully addressed. In this work, we characterised triacylglycerol (TAG) and polar lipid profiles of the olive pulp while using a complementary methodological approach that was based on solid-phase extraction to recover the neutral lipid (NL) and the polar lipid-rich fractions. The TAG profile was analysed in the NL-fraction by C₃₀ reversed-phase liquid chromatography (LC) and the polar lipid profile by normal-phase hydrophilic interaction liquid chromatography (HILIC), with both being coupled to electrospray ionization-mass spectrometry (ESI-MS) and ESI-MS/MS. This approach identified 71 TAG ions that were attributed to more than 350 molecular species, with fatty acyl chain lengths from C11:0 to C26:0, including different polyunsaturated acyl chains. The polar lipids included 107 molecular species that belonged to 11 lipid classes that comprised phospholipids, glyceroglycolipids, glycosphingolipids, and betaine lipids. In addition to polyunsaturated fatty acids, some of the phospholipids, glycolipids, and glycosphingolipids that were identified in the olive pulp have been described as biologically active molecules. Lipidomic phenotyping of the olive pulp has led to the discovery of compounds that will allow for a better assessment of its nutritional value and new applications of bioactive lipid components in this functional food.

Glucosylceramides From Lomentospora prolificans Induce a Differential Production of Cytokines and Increases the Microbicidal Activity of Macrophages

Lomentospora prolificans is an emerging opportunistic fungus with a high resistance to antifungal agents and it can cause localized infections in immunocompetent patients and disseminated infections with a high mortality rate in immunosuppressed patients. Glucosylceramides (GlcCer) are synthetized in the majority of known fungal pathogens. They are bioactive molecules presenting different functions, such as involvement in fungal growth and morphological transitions in several fungi. The elucidation of the primary structure of the fungal surface glycoconjugates could contribute for the understanding of the mechanisms of pathogenicity. In this work, GlcCer species were isolated from mycelium and conidia forms of L. prolificans and their chemical structures were elucidated by mass spectrometry (ESI-MS). GlcCer purified from both forms presented a major species at m/z 750 that corresponds to N-2-hydroxyhexadecanoyl-1-β-D-glucopyranosyl-9-methyl-4,8-sphingadienine. Monoclonal antibodies against GlcCer could recognize L. prolificans GlcCer species from mycelium and conidia, suggesting a conserved epitope in fungal GlcCer. In addition, in vivo assays showed that purified GlcCer species from both forms was able to induce a high secretion of pro-inflammatory cytokines by splenocytes. GlcCer species also promote the recruitment of polymorphonuclear, eosinophils, small peritoneal macrophage (SPM) and mononuclear cells to the peritoneal cavity. GlcCer species were also able to induce the oxidative burst by peritoneal macrophages with NO and superoxide radicals production, and to increase the killing of L. prolificans conidia by peritoneal macrophages. These results indicate that GlcCer species from L. prolificans are a potent immune response activator.

Chemistry and Biology of Bioactive Glycolipids of Marine Origin

Glycolipids represent a broad class of natural products structurally featured by a glycosidic fragment linked to a lipidic molecule. Despite the large structural variety of these glycoconjugates, they can be classified into three main groups, i.e., glycosphingolipids, glycoglycerolipids, and atypical glycolipids. In the particular case of glycolipids derived from marine sources, an impressive variety in their structural features and biological properties is observed, thus making them prime targets for chemical synthesis. In the present review, we explore the chemistry and biology of this class of compounds.

Scedosporium apiospermum, Scedosporium aurantiacum, Scedosporium minutisporum and Lomentospora prolificans: a comparative study of surface molecules produced by conidial and germinated conidial cells

BACKGROUND

Scedosporium/Lomentospora species are opportunistic mould pathogens, presenting notable antifungal resistance.

OBJECTIVES/METHODS

We analysed the conidia and germinated conidia of S. apiospermum (Sap), S. aurantiacum (Sau), S. minutisporum (Smi) and L. prolificans (Lpr) by scanning electron microscopy and exposition of surface molecules by fluorescence microscopy.

FINDINGS

Conidia of Sap, Smi and Sau had oval, ellipsoidal and cylindrical shape, respectively, with several irregularities surrounding all surface areas, whereas Lpr conidia were rounded with a smooth surface. The germination of Sap occurred at the conidial bottom, while Smi and Sau germination primarily occurred at the centre of the conidial cell, and Lpr germination initiated at any part of the conidial surface. The staining of N-acetylglucosamine-containing molecules by fluorescein-labelled WGA primarily occurred during the germination of all studied fungi and in the conidial scars, which is the primary location of germination. Calcofluor white, which recognises the polysaccharide chitin, strongly stained the conidial cells and, to a lesser extent, the germination. Both mannose-rich glycoconjugates (evidenced by fluoresceinated-ConA) and cell wall externally located polypeptides presented distinct surface locations and expression according to both morphotypes and fungal species. In contrast, sialic acid and galactose-containing structures were not detected at fungal surfaces.

MAIN CONCLUSIONS

The present study demonstrated the differential production/exposition of surface molecules on distinct morphotypes of Scedosporium/Lomentospora species.

Monohexosylceramides from Rhizopus Species Isolated from Brazilian Caatinga: Chemical Characterization and Evaluation of Their Anti-Biofilm and Antibacterial Activities

Monohexosylceramides (CMHs) are highly conserved fungal glycosphingolipids playing a role in several cellular processes such as growth, differentiation and morphological transition. In this study, we report the isolation, purification and chemical characterization of CMHs from Rhizopus stolonifer and R. microspores. Using positive ion mode ESI-MS, two major ion species were observed at m/z 750 and m/z 766, respectively. Both ion species consisted of a glucose/galactose residue attached to a ceramide moiety containing 9-methyl-4,8-sphingadienine with an amidic linkage to a hydroxylated C16:0 fatty acid. The antimicrobial activity of CMH was evaluated against Gram positive and Gram negative bacteria using the agar diffusion assay. CMH from both Rhizopus species inhibited the growth of Bacillus terrae, Micrococcus luteus (M. luteus) and Pseudomonas stutzeri (P. stutzeri) with a MIC₅₀ of 6.25, 6.25 and 3.13 mg/mL, respectively. The bactericidal effect was detected only for M. luteus and P. stutzeri, with MBC values of 25 and 6.25 mg/mL, respectively. Furthermore, the action of CMH on the biofilm produced by methicillin-resistant Staphylococcus aureus (MRSA) was analyzed using 12.5 and 25 mg/mL of CMH from R. microsporus. Total biofilm biomass, biofilm matrix and viability of the cells that form the biofilm structure were evaluated. CMH from R. microsporus was able to inhibit the MRSA biofilm formation in all parameters tested.

A Sphingosine-type cerebroside in Clavicorona pyxidata induce fruit body formation

Clavicorona pyxidata is a wild edible and medicinal mushroom that is rich in bioactive natural products and has thus been extensively used as traditional medicine in China. The present study has determined that the organic crude extract prepared from a fermented culture of C. pyxidata imparted auto-inhibitory effects on mycelial growth and then induced the formation of fruiting bodies. By monitoring bioactivity, one compound was isolated via successive chromatography over silica gel, Sephadex LH-20, and Cl8-reversed phase silica gel and was identified as a known sphingosine-type cerebroside by nuclear magnetic resonance (NMR) and physicochemical data, namely, (4E, 8E)-N-D-2'-hydroxypalmitoyl-1-O-β-D-glucopyranosyl-9-methyl-4,8-sphingadienine. The application of this cerebroside at a concentration of 200 μg/disc paper resulted in the inhibition of aerial hyphal growth of C. pyxidata. The findings of the present study indicated that this C. pyxidata cerebroside is a fruiting body-inducing substance (FIS).

Cerebrosides, extracellular glycolipids secreted by the selective lignin-degrading fungus Ceriporiopsis subvermispora

Ceriporiopsis subvermispora is a selective white-rot fungus that degrades lignin at a site far from the hyphae and extracellular enzymes, without intensive damage to the cellulose. In selective ligninolysis, low molecular mass metabolites play a principal role and amphipathic substances are involved to control the degradation and transport of hydrophobic aromatic molecules, including lignin and lipids; however, secretion of the amphipathic substances by this fungus has not been well understood, except for alk(en)yl itaconates called ceriporic acids, which have a weak amphiphilicity. Herein, we report for the first time that the fungus secretes cerebrosides that are classified as glycosphingolipids. By using liquid chromatography electron spray ionization mass spectrometry (LC-ESI-MS) and nuclear magnetic resonance (NMR) spectroscopy coupled with stable isotope feeding experiments with ¹³C-glucose and ¹⁵N-ammonium sulfate, the cerebrosides were determined to be N-hydroxyoctadecanoyl-1-O-β-d-glucopyranosyl-4E,8E-sphingadienine, N-hydroxyoctadecanoyl-1-O-β-d-glucopyranosyl-4E,8Z-sphingadienine, and N-hydroxyoctadecanoyl-1-O-β-d-glucopyranosyl-9-methyl-4E,8E-sphingadienine. The cerebrosides are strong amphipathic substances and potential metabolites for regulating difference and symbiosis within the microbial community.

The Role of Hydrophobicity and Surface Receptors at Hyphae of Lyophyllum sp. Strain Karsten in the Interaction with Burkholderia terrae BS001 - Implications for Interactions in Soil

The soil bacterium Burkholderia terrae strain BS001 can interact with varying soil fungi, using mechanisms that range from the utilization of carbon/energy sources such as glycerol to the ability to reach novel territories in soil via co-migration with growing fungal mycelia. Here, we investigate the intrinsic properties of the B. terrae BS001 interaction with the basidiomycetous soil fungus Lyophyllum sp. strain Karsten. In some experiments, the ascomycetous Trichoderma asperellum 302 was also used. The hyphae of Lyophyllum sp. strain Karsten were largely hydrophilic on water-containing media versus hydrophobic when aerial, as evidenced by contact angle analyses (CA). Co-migration of B. terrae strain BS001 cells with the hyphae of the two fungi occurred preferentially along the - presumably hydrophilic - soil-dwelling hyphae, whereas aerial hyphae did not allow efficient migration, due to reduced thickness of their surrounding mucous films. Moreover, the cell numbers over the length of the hyphae in soil showed an uneven distribution, i.e., the CFU numbers increased from minima at the inoculation point to maximal numbers in the middle of the extended hyphae, then decreasing toward the terminal side. Microscopic analyses of the strain BS001 associations with the Lyophyllum sp. strain Karsten hyphae in the microcosms confirmed the presence of B. terrae BS001 cells on the mucous matter that was present at the hyphal surfaces of the fungi used. Cell agglomerates were found to accumulate at defined sites on the hyphal surfaces, which were coined ‘fungal-interactive’ hot spots. Evidence was further obtained for the contention that receptors for a physical bacterium-fungus interaction occur at the Lyophyllum sp. strain Karsten hyphal surface, in which the specific glycosphingolipid ceramide monohexoside (CMH) plays an important role. Thus, bacterial adherence may be mediated by heterogeneously distributed fungal-specific receptors, implying the CMH moieties. This study sheds light on the physical aspects of the B. terrae BS001 – Lyophyllum sp. strain Karsten interaction, highlighting heterogeneity along the hyphae with respect to hydrophobicity and the presence of potential anchoring sites.

Chemotaxis and adherence to fungal surfaces are key components of the behavioral response of Burkholderia terrae BS001 to two selected soil fungi

Burkholderia terrae BS001 has previously been proposed to be a 'generalist' associate of soil fungi, but its strategies of interaction have been largely ignored. Here, we studied the chemotactic behavior of B. terrae BS001 towards Lyophyllum sp. strain Karsten and Trichoderma asperellum 302 and the role of fungal surface molecules in their physical interaction with the bacteria. To assess the involvement of the type 3 secretion system (T3SS), wild-type strain BS001 and T3SS mutant strain BS001-ΔsctD were used in the experiments. First, the two fungi showed divergent behavior when confronted with B. terrae BS001 on soil extract agar medium. Lyophyllum sp. strain Karsten revealed slow growth towards the bacterium, whereas T. asperellum 302 grew avidly over it. Both on soil extract and M9 agar, B. terrae BS001 and BS001-ΔsctD moved chemotactically towards the hyphae of both fungi, with a stronger response to Lyophyllum sp. strain Karsten than to T. asperellum 302. The presence of a progressively increasing glycerol level in the M9 agar enhanced the level of movement. Different oxalic acid concentrations exerted varied effects, with a significantly raised chemotactic response at lower, and a subdued response at higher concentrations. Testing of the adherence of B. terrae BS001 and BS001-ΔsctD to Lyophyllum sp. strain Karsten and to cell envelope-extracted ceramide monohexosides (CMHs) revealed that CMHs in both conidia and hyphae could bind strain BS001 cells. As BS001-ΔsctD adhered significantly less to the CMHs than BS001, the T3SS was presumed to have a role in the interaction. In contrast, such avid adherence was not detected with T. asperellum 302. Thus, B. terrae BS001 shows a behavior characterized by swimming towards Lyophyllum sp. strain Karsten and T. asperellum 302 and attachment to the CMH moiety in the cell envelope, in particular of the former.

Psd1 binding affinity toward fungal membrane components as assessed by SPR: The role of glucosylceramide in fungal recognition and entry

Psd1 is a plant defensin that has antifungal activity against several pathogenic and nonpathogenic fungi. Previous analysis of Psd1 chemical shift perturbations by nuclear magnetic resonance (NMR) spectroscopy demonstrated that this defensin interacts with phospholipids and the sphingolipid glucosylceramide isolated from Fusarium solani (GlcCer(Fusarium solani)). In this study, these interactions were evaluated by real-time surface plasmon resonance (SPR) analysis. The data obtained demonstrated that Psd1 could bind more strongly to small unilamellar vesicles (SUV)-containing GlcCer(Fusarium solani) than to SUV that was composed of phosphatidylcholine (PC) alone or was enriched with GlcCer that had been isolated from soybeans. An increase in the SPR response after cholesterol or ergosterol incorporation in PC-SUV was detected; however, SUV composed of PC:Erg (7:3; molar:molar) became unstable in the presence of Psd1, suggesting membrane destabilization. We also observed a lack of Psd1 internalization in Candida albicans strains that were deficient in the glucosyl ceramide synthase gene. Together, these data indicate that GlcCer is essential for Psd1 anchoring in the fungal plasma membrane as well as internalization.

Tools for the analysis of metabolic flux through the sphingolipid pathway

Discerning the complex regulation of the enzymatic steps necessary for sphingolipid biosynthesis is facilitated by the utilization of tracers that allow a time-resolved analysis of the pathway dynamics without affecting the metabolic flux. Different strategies have been used and new tools are continuously being developed to probe the various enzymatic conversions that occur within this complex pathway. Here, we provide a short overview of the divergent fungal and mammalian sphingolipid biosynthetic routes, and of the tracers and methods that are frequently employed to follow the flux of intermediates throughout these pathways.

Sphingolipidomics: An Important Mechanistic Tool for Studying Fungal Pathogens

Sphingolipids form of a unique and complex group of bioactive lipids in fungi. Structurally, sphingolipids of fungi are quite diverse with unique differences in the sphingoid backbone, amide linked fatty acyl chain and the polar head group. Two of the most studied and conserved sphingolipid classes in fungi are the glucosyl- or galactosyl-ceramides and the phosphorylinositol containing phytoceramides. Comprehensive structural characterization and quantification of these lipids is largely based on advanced analytical mass spectrometry based lipidomic methods. While separation of complex lipid mixtures is achieved through high performance liquid chromatography, the soft - electrospray ionization tandem mass spectrometry allows a high sensitivity and selectivity of detection. Herein, we present an overview of lipid extraction, chromatographic separation and mass spectrometry employed in qualitative and quantitative sphingolipidomics in fungi.

Antibodies Against Glycolipids Enhance Antifungal Activity of Macrophages and Reduce Fungal Burden After Infection with Paracoccidioides brasiliensis

Paracoccidioidomycosis is a fungal disease endemic in Latin America. Polyclonal antibodies to acidic glycosphingolipids (GSLs) from Paracoccidioides brasiliensis opsonized yeast forms in vitro increasing phagocytosis and reduced the fungal burden of infected animals. Antibodies to GSL were active in both prophylactic and therapeutic protocols using a murine intratracheal infection model. Pathological examination of the lungs of animals treated with antibodies to GSL showed well-organized granulomas and minimally damaged parenchyma compared to the untreated control. Murine peritoneal macrophages activated by IFN-γ and incubated with antibodies against acidic GSLs more effectively phagocytosed and killed P. brasiliensis yeast cells as well as produced more nitric oxide compared to controls. The present work discloses a novel target of protective antibodies against P. brasiliensis adding to other well-studied mediators of the immune response to this fungus.

Fungal glycans and the innate immune recognition

Polysaccharides such as α- and β-glucans, chitin, and glycoproteins extensively modified with both N- and O-linked carbohydrates are the major components of fungal surfaces. The fungal cell wall is an excellent target for the action of antifungal agents, since most of its components are absent from mammalian cells. Recognition of these carbohydrate-containing molecules by the innate immune system triggers inflammatory responses and activation of microbicidal mechanisms by leukocytes. This review will discuss the structure of surface fungal glycoconjugates and polysaccharides and their recognition by innate immune receptors.

Structural analysis of cerebrosides from Aspergillus fungi: the existence of galactosylceramide in A. oryzae

Glucosylceramide and galactosylceramide were detected in three Aspergillus species: Aspergillus oryzae, Aspergillus sojae and Aspergillus. awamori, using borate-coated TLC. The cerebrosides from A. oryzae were further purified by ion exchange and iatrobeads column chromatographies with or without borate, and determined the composition of sugar, fatty acid and sphingoid base by GC/MS, MALDI-TOF/MS and (1)H-NMR. We identified them as β-glucosylceramide and β-galactosylceramide. The ceramide moiety of both cerebrosides consisted mainly of 2-hydroxystearic acid and either 9-methyl-octadeca-4, 8-sphingadienine or octadeca-4, 8-sphingadienine. To our knowledge, this is the first study to provide evidence for the presence of β-galactosylceramide in A. oryzae.

Characterization of Scedosporium apiospermum glucosylceramides and their involvement in fungal development and macrophage functions

Scedosporium apiospermum is an emerging fungal pathogen that causes both localized and disseminated infections in immunocompromised patients. Glucosylceramides (CMH, GlcCer) are the main neutral glycosphingolipids expressed in fungal cells. In this study, glucosylceramides (GlcCer) were extracted and purified in several chromatographic steps. Using high-performance thin layer chromatography (HPTLC) and electrospray ionization mass spectrometry (ESI-MS), N-2′-hydroxyhexadecanoyl-1-β-D-glucopyranosyl-9-methyl-4,8-sphingadienine was identified as the main GlcCer in S. apiospermum. A monoclonal antibody (Mab) against this molecule was used for indirect immunofluorescence experiments, which revealed that this CMH is present on the surface of the mycelial and conidial forms of S. apiospermum. Treatment of S. apiospermum conidia with the Mab significantly reduced fungal growth. In addition, the Mab also enhanced the phagocytosis and killing of S. apiospermum by murine cells. In vitro assays were performed to evaluate the CMHs for their cytotoxic activities against the mammalian cell lines L.929 and RAW, and an inhibitory effect on cell proliferation was observed. Synergistic invitro interactions were observed between the Mab against GlcCer and both amphotericin B (AmB) and itraconazole. Because Scedosporium species develop drug resistance, the number of available antifungal drugs is limited; our data indicate that combining immunotherapy with the available drugs might be a viable treatment option. These results suggest that in S. apiospermum, GlcCer are most likely cell wall components that are targeted by antifungal antibodies, which directly inhibit fungal development and enhance macrophage function; furthermore, these results suggest the combined use of monoclonal antibodies against GlcCer and antifungal drugs for antifungal immunotherapy.

Antiviral Sulfoquinovosyldiacylglycerols (SQDGs) from the Brazilian brown seaweed Sargassum vulgare

Total lipids from the Brazilian brown seaweed Sargassum vulgare were extracted with chloroform/methanol 2:1 and 1:2 (v/v) at room temperature. After performing Folch partition of the crude lipid extract, the lipids recovered from the Folch lower layer were fractionated on a silica gel column eluted with chloroform, acetone and methanol. The fraction eluted with methanol, presented a strong orcinol-positive band characteristic of the presence of sulfatides when examined by TLC. This fraction was then purified by two successive silica gel column chromatography giving rise to fractions F4I86 and F4II90 that exhibited strong activity against herpes simplex virus type 1 and 2. The chemical structures present in both fractions were elucidated by ESI-MS and ¹H/¹³C NMR analysis HSQC fingerprints based on their tandem-MS behavior as Sulfoquinovosyldiacylglycerols (SQDGs). The main SQDG present in both fractions and responsible for the anti-herpes activity observed was identified as 1,2-di-O-palmitoyl-3-O-(6-sulfo-α-D-quinovopyranosyl)-glycerol.

Practical multigram-scale synthesis of 4,6- and 4,8-sphingadienes, chemopreventive sphingoid bases

Sphingadienes are chemopreventive agents that act by blocking signaling pathways that are activated in cancer. A practical synthesis of 4,6- and 4,8-sphingadienes on a scale of gram quantities is reported here in order to allow evaluation of the biological properties of these sphingolipids. The key steps in the preparation of 4,6-sphingadiene (1a) are an intramolecular cyclization of N-Boc derivative 5a to oxazolidinone derivative 6a, followed by conversion to carbamate intermediate 7a and base-mediated hydrolysis to afford the product without further purification. 4,8-Sphingadiene (1b) was prepared in a similar fashion; the requisite trans-γ,δ-unsaturated aldehyde 15 was prepared by an ester enolate Ireland-Claisen rearrangement.

Structural characterization and anti-HSV-1 and HSV-2 activity of glycolipids from the marine algae Osmundaria obtusiloba isolated from Southeastern Brazilian coast

Glycolipids were extracted from the red alga Osmundaria obtusiloba from Southeastern Brazilian coast. The acetone insoluble material was extracted with chloroform/methanol and the lipids, enriched in glycolipids, were fractionated on a silica gel column eluted with chloroform, acetone and then methanol. Three major orcinol-positive bands were found in the acetone and methanol fractions, being detected by thin layer chromatography. The structures of the corresponding glycolipids were elucidated by ESI-MS and ¹H/¹³C NMR analysis, on the basis of their tandem-MS behavior and HSQC, TOCSY fingerprints. For the first time, the structure of sulfoquinovosyldiacylglycerol from the red alga Osmundaria obtusiloba was characterized. This molecule exhibited potent antiviral activity against HSV-1 and HSV-2 with EC₅₀ values of 42 µg/mL to HSV-1 and 12 µg/mL to HSV-2, respectively. Two other glycolipids, mono- and digalactosyldiacylglycerol, were also found in the alga, being characterized by ESI-MS/MS. The structural elucidation of algae glycolipids is a first step for a better understanding of the relation between these structures and their biological activities.