Corrected and republished from: "Extracellular Vesicle Formation in Cryptococcus deuterogattii Impacts Fungal Virulence".

Small molecules are components of fungal extracellular vesicles (EVs), but their biological roles are only superficially known. NOP16 is a eukaryotic gene that is required for the activity of benzimidazoles against Cryptococcus deuterogattii. In this study, during the phenotypic characterization of C. deuterogattii mutants expected to lack NOP16 expression, we observed a reduced EV production. Whole-genome sequencing, RNA-Seq, and cellular proteomics revealed that, contrary to our initial findings, these mutants expressed Nop16 but exhibited altered expression of 14 genes potentially involved in sugar transport. Based on this observation, we designated these mutant strains as Past1 and Past2, representing potentially altered sugar transport. Analysis of the small molecule composition of EVs produced by wild-type cells and the Past1 and Past2 mutant strains revealed not only a reduced number of EVs but also an altered small molecule composition. In a Galleria mellonella model of infection, the Past1 and Past2 mutant strains were hypovirulent. The hypovirulent phenotype was reverted when EVs produced by wild-type cells, but not mutant EVs, were co-injected with the mutant cells in G. mellonella. These results connect EV biogenesis, cargo, and cryptococcal virulence.

ß-1,3-Glucan recognition by Acanthamoeba castellanii as a putative mechanism of amoeba-fungal interactions.

In this study, we conducted an in-depth analysis to characterize potential Acanthamoeba castellanii (Ac) proteins capable of recognizing fungal ß-1,3-glucans. Ac specifically anchors curdlan or laminarin, indicating the presence of surface ß-1,3-glucan-binding molecules. Using optical tweezers, strong adhesion of laminarin- or curdlan-coated beads to Ac was observed, highlighting their adhesive properties compared to controls (characteristic time τ of 46.9 and 43.9 s, respectively). Furthermore, Histoplasma capsulatum (Hc) G217B, possessing a ß-1,3-glucan outer layer, showed significant adhesion to Ac compared to a Hc G186 strain with an α-1,3-glucan outer layer (τ of 5.3 s vs τ 83.6 s). The addition of soluble ß-1,3-glucan substantially inhibited this adhesion, indicating the involvement of ß-1,3-glucan recognition. Biotinylated ß-1,3-glucan-binding proteins from Ac exhibited higher binding to Hc G217B, suggesting distinct recognition mechanisms for laminarin and curdlan, akin to macrophages. These observations hinted at the ß-1,3-glucan recognition pathway's role in fungal entrance and survival within phagocytes, supported by decreased fungal viability upon laminarin or curdlan addition in both phagocytes. Proteomic analysis identified several Ac proteins capable of binding ß-1,3-glucans, including those with lectin/glucanase superfamily domains, carbohydrate-binding domains, and glycosyl transferase and glycosyl hydrolase domains. Notably, some identified proteins were overexpressed upon curdlan/laminarin challenge and also demonstrated high affinity to ß-1,3-glucans. These findings underscore the complexity of binding via ß-1,3-glucan and suggest the existence of alternative fungal recognition pathways in Ac.IMPORTANCEAcanthamoeba castellanii (Ac) and macrophages both exhibit the remarkable ability to phagocytose various extracellular microorganisms in their respective environments. While substantial knowledge exists on this phenomenon for macrophages, the understanding of Ac's phagocytic mechanisms remains elusive. Recently, our group identified mannose-binding receptors on the surface of Ac that exhibit the capacity to bind/recognize fungi. However, the process was not entirely inhibited by soluble mannose, suggesting the possibility of other interactions. Herein, we describe the mechanism of ß-1,3-glucan binding by A. castellanii and its role in fungal phagocytosis and survival within trophozoites, also using macrophages as a model for comparison, as they possess a well-established mechanism involving the Dectin-1 receptor for ß-1,3-glucan recognition. These shed light on a potential parallel evolution of pathways involved in the recognition of fungal surface polysaccharides.

Extracellular Vesicle Formation in Cryptococcus deuterogattii Impacts Fungal Virulence and Requires the NOP16 Gene.

Small molecules are components of fungal extracellular vesicles (EVs), but their biological roles are only superficially known. NOP16 is a eukaryotic gene that is required for the activity of benzimidazoles against Cryptococcus deuterogattii. In this study, during the phenotypic characterization of C. deuterogattii mutants lacking NOP16 expression, we observed that this gene was required for EV production. Analysis of the small molecule composition of EVs produced by wild-type cells and two independent nop16Δ mutants revealed that the deletion of NOP16 resulted not only in a reduced number of EVs but also an altered small molecule composition. In a Galleria mellonella model of infection, the nop16Δ mutants were hypovirulent. The hypovirulent phenotype was reverted when EVs produced by wild-type cells, but not mutant EVs, were coinjected with the nop16Δ cells in G. mellonella. These results reveal a role for NOP16 in EV biogenesis and cargo, and also indicate that the composition of EVs is determinant for cryptococcal virulence.

Fungal Extracellular Vesicles as a Potential Strategy for Vaccine Development.

Extracellular vesicles (EVs) are released by virtually all live cells. In fungal organisms, the EVs traverse the cell wall and reach the extracellular environment, where they can interact with host cells and potentially impact the disease outcome. Compositional analyses have demonstrated that fungal EVs carry lipids, proteins, polysaccharides, glycans, nucleic acids, and a diversity of small metabolites. Among this variety of compounds, several molecules with immunogenic properties were characterized. It corroborates with their ability to stimulate innate immune cells, induce antibody production and protect insects and mice against fungal infections. In this chapter, we discuss the advantages of using fungal EVs as a new platform for the development of antifungal vaccines.

Current Microscopy Strategies to Image Fungal Vesicles: From the Intracellular Trafficking and Secretion to the Inner Structure of Isolated Vesicles.

Extracellular vesicles (EVs) are nano-sized structures that play important roles in a variety of biological processes among members of the Eukaryota domain. They have been studied since the 1940s and a broader use of different microscopy techniques to image either isolated vesicles or vesicles within the intracellular milieu (trafficking) has been limited by their nanometric size, usually below the resolution limit of most standard light microscopes. The development of genetically encoded fluorescent proteins and fluorescent probes able to switch between "on" and "off" states, as well the improvement in computer-assisted microscopy, photon detector devices, illumination designs, and imaging strategies in the late Twentieth century, boosted the use of light microscopes to provide structural and functional information at the sub-diffraction resolution, taking advantage of a nondestructive analytical probe such light, and opening new possibilities in the study of life at the nanoscale. As well, traditional and novel electron microscopy techniques have been widely used in the characterization of subcellular compartments, either isolated or in situ, providing a comprehensive understanding of their functional role in many cellular processes. Here, we present basic aspects of some of these techniques that have already been applied and their potential application to the study of fungal vesicles.

Host cell membrane microdomains and fungal infection.

Lipid microdomains or lipid rafts are dynamic and tightly ordered regions of the plasma membrane. In mammalian cells, they are enriched in cholesterol, glycosphingolipids, Glycosylphosphatidylinositol-anchored and signalling-related proteins. Several studies have suggested that mammalian pattern recognition receptors are concentrated or recruited to lipid domains during host-pathogen association to enhance the effectiveness of host effector processes. However, pathogens have also evolved strategies to exploit these domains to invade cells and survive. In fungal organisms, a complex cell wall network usually mediates the first contact with the host cells. This cell wall may contain virulence factors that interfere with the host membrane microdomains dynamics, potentially impacting the infection outcome. Indeed, the microdomain disruption can dampen fungus-host cell adhesion, phagocytosis and cellular immune responses. Here, we provide an overview of regulatory strategies employed by pathogenic fungi to engage with and potentially subvert the lipid microdomains of host cells. TAKE AWAY: Lipid microdomains are ordered regions of the plasma membrane enriched in cholesterol, glycosphingolipids (GSL), GPI-anchored and signalling-related proteins. Pathogen recognition by host immune cells can involve lipid microdomain participation. During this process, these domains can coalesce in larger complexes recruiting receptors and signalling proteins, significantly increasing their signalling abilities. The antifungal innate immune response is mediated by the engagement of pathogen-associated molecular patterns to pattern recognition receptors (PRRs) at the plasma membrane of innate immune cells. Lipid microdomains can concentrate or recruit PRRs during host cell-fungi association through a multi-interactive mechanism. This association can enhance the effectiveness of host effector processes. However, virulence factors at the fungal cell surface and extracellular vesicles can re-assembly these domains, compromising the downstream signalling and favouring the disease development. Lipid microdomains are therefore very attractive targets for novel drugs to combat fungal infections.

In vitro and in vivo efficacies of Dectin-1-Fc(IgG)(s) fusion proteins against invasive fungal infections.

Fungal infections have increased in the last years, particularly associated to an increment in the number of immunocompromised individuals and the emergence of known or new resistant species, despite the difficulties in the often time-consuming diagnosis. The controversial efficacy of the currently available strategies for their clinical management, apart from their high toxicity and severe side effects, has renewed the interest in the research and development of new broad antifungal alternatives. These encompass vaccines and passive immunization strategies with monoclonal antibodies (mAbs), recognizing ubiquitous fungal targets, such as fungal cell wall ß-1,3-glucan polysaccharides, which could be used in early therapeutic intervention without the need for the diagnosis at species level. As additional alternatives, based on the Dectin-1 great affinity to ß-1,3-glucan, our group developed broad antibody-like Dectin1-Fc(IgG)(s) from distinct subclasses (IgG2a and IgG2b) and compared their antifungal in vitro and passive immunizations in vivo performances. Dectin1-Fc(IgG2a) and Dectin1-Fc(IgG2b) demonstrated high affinity to laminarin and the fungal cell wall by ELISA, flow cytometry, and microscopy. Both Dectin-1-Fc(IgG)(s) inhibited Histoplasma capsulatum and Cryptococcus neoformans growth in a dose-dependent fashion. For Candida albicans, such inhibitory effect was observed with concentrations as low as 0.098 and 0.049 µg/ml, respectively, which correlated with the impairment of the kinetics and lengths of germ tubes in comparison to controls. Previous opsonization with Dectin-1-Fc(IgG)(s) enhanced considerably the macrophage antifungal effector functions, increasing the fungi macrophages interactions and significantly reducing the intraphagosome fungal survival, as lower CFUs were observed. The administration of both Dectin1-Fc(IgG)(s) reduced the fungal burden and mortality in murine histoplasmosis and candidiasis models, in accordance with previous evaluations in aspergillosis model. These results altogether strongly suggested that therapeutic interventions with Dectin-1-Fc(IgG)(s) fusion proteins could directly impact the innate immunity and disease outcome in favor of the host, by direct neutralization, opsonization, phagocytosis, and fungal elimination, providing interesting information on the potential of these new strategies for the control of invasive fungal infections. LAY SUMMARY: Mycoses have increased worldwide, and new efficient therapeutics are needed. Passive immunizations targeting universally the fungal cell would allow early interventions without the species-level diagnosis. Lectins with affinity to carbohydrates could be used to engineer 'antibody-like' strategies.

Antifungal activity of Acylhydrazone derivatives against Sporothrix spp.

Sporotrichosis is an emerging mycosis caused by members of the genus Sporothrix The disease affects humans and animals, particularly cats, which plays an important role in the zoonotic transmission. Feline sporotrichosis treatment options include itraconazole (ITC), potassium iodide and amphotericin B, drugs usually associated with deleterious adverse reactions and refractoriness in cats, especially when using ITC. Thus, affordable, non-toxic and clinically effective anti-Sporothrix agents are needed. Recently, acylhydrazones (AH), molecules targeting vesicular transport and cell cycle progression, exhibited a potent antifungal activity against several fungal species and displayed low toxicity when compared to the current drugs. In this work, the AH derivatives D13 and SB-AF-1002 were tested against Sporothrix schenckii and Sporothrix brasiliensis Minimal inhibitory concentrations of 0.12 - 1 µg/mL were observed for both species in vitro D13 and SB-AF-1002 showed an additive effect with itraconazole. Treatment with D13 promoted yeast disruption with release of intracellular components, as confirmed by transmission electron microscopy of S. brasiliensis exposed to the AH derivatives. AH-treated cells displayed thickening of the cell wall, discontinuity of the cell membrane and an intense cytoplasmic degeneration. In a murine model of sporotrichosis, treatment with AH derivatives was more efficient than ITC, the drug of choice for sporotrichosis. The results of the preliminary clinical study in cats indicate that D13 is safe and has potential to become a therapeutic option for sporotrichosis when associated to ITC. Our results expand the antifungal broadness of AH derivatives and suggest that these drugs could be exploited to combat sporotrichosis.

Media matters! Alterations in the loading and release of Histoplasma capsulatum extracellular vesicles in response to different nutritional milieus.

Histoplasma capsulatum is a dimorphic fungus that most frequently causes pneumonia, but can also disseminate and proliferate in diverse tissues. Histoplasma capsulatum has a complex secretion system that mediates the release of macromolecule-degrading enzymes and virulence factors. The formation and release of extracellular vesicles (EVs) are an important mechanism for non-conventional secretion in both ascomycetes and basidiomycetes. Histoplasma capsulatum EVs contain diverse proteins associated with virulence and are immunologically active. Despite the growing knowledge of EVs from H. capsulatum and other pathogenic fungi, the extent that changes in the environment impact the sorting of organic molecules in EVs has not been investigated. In this study, we cultivated H. capsulatum with distinct culture media to investigate the potential plasticity in EV loading in response to differences in nutrition. Our findings reveal that nutrition plays an important role in EV loading and formation, which may translate into differences in biological activities of these fungi in various fluids and tissues.

Protective effect of fungal extracellular vesicles against murine candidiasis.

Extracellular vesicles (EVs) are lipid bilayered compartments released by virtually all living cells, including fungi. Among the diverse molecules carried by fungal EVs, a number of immunogens, virulence factors and regulators have been characterised. Within EVs, these components could potentially impact disease outcomes by interacting with the host. From this perspective, we previously demonstrated that EVs from Candida albicans could be taken up by and activate macrophages and dendritic cells to produce cytokines and express costimulatory molecules. Moreover, pre-treatment of Galleria mellonella larvae with fungal EVs protected the insects against a subsequent lethal infection with C. albicans yeasts. These data indicate that C. albicans EVs are multi-antigenic compartments that activate the innate immune system and could be exploited as vaccine formulations. Here, we investigated whether immunisation with C. albicans EVs induces a protective effect against murine candidiasis in immunosuppressed mice. Total and fungal antigen-specific serum IgG antibodies increased by 21 days after immunisation, confirming the efficacy of the protocol. Vaccination decreased fungal burden in the liver, spleen and kidney of mice challenged with C. albicans. Splenic levels of cytokines indicated a lower inflammatory response in mice immunised with EVs when compared with EVs + Freund's adjuvant (ADJ). Higher levels of IL-12p70, TNFα and IFNγ were detected in mice vaccinated with EVs + ADJ, while IL-12p70, TGFß, IL-4 and IL-10 were increased when no adjuvants were added. Full protection of lethally challenged mice was observed when EVs were administered, regardless the presence of adjuvant. Physical properties of the EVs were also investigated and EVs produced by C. albicans were relatively stable after storage at 4, -20 or -80°C, keeping their ability to activate dendritic cells and to protect G. mellonella against a lethal candidiasis. Our data suggest that fungal EVs could be a safe source of antigens to be exploited in vaccine formulations.

Silver chitosan nanocomposites as a potential treatment for superficial candidiasis.

Silver compounds are widely known for their antimicrobial activity, but can exert toxic effects to the host. Among the strategies to reduce its toxicity, incorporation into biopolymers has shown promising results. We investigated the green syntheses of silver nanoparticles (AgNPs) and their functionalization in a chitosan matrix (AgNPs@Chi) as a potential treatment against Candida spp. Inhibitory concentrations ranging between 0.06 and  1 µg/ml were observed against distinct Candida species. Nanocomposite-treated cells displayed cytoplasmic degeneration and a cell membrane and wall disruption. Silver nanocomposites in combination with fluconazole and amphotericin B showed an additive effect when analyzed by the Bliss method. The low cytotoxicity displayed in mammalian cells and in the Galleria mellonella larvae suggested their potential use in vivo. When tested as a topical treatment against murine cutaneous candidiasis, silver nanocomposites reduced the skin fungal burden in a dose-response behavior and favored tissue repair. In addition, the anti-biofilm effect of AgNPs@Chi in human nail model was demonstrated, suggesting that the polymeric formulation of AgNPs does not affect antifungal activity even against sessile cells. Our results suggest that AgNPs@Chi seems to be a less toxic and effective topical treatment for superficial candidiasis. LAY SUMMARY: This study demonstrated the efficacy of silver nanoparticles (AgNPs) in inhibiting the growth of Candida. AgNPs incorporated in chitosan displayed a reduced toxicity. Tests in infected mice showed the effectiveness of the treatment. AgNPs-chitosan could be an alternative to combat candidiasis.

Host membrane glycosphingolipids and lipid microdomains facilitate Histoplasma capsulatum internalisation by macrophages.

Recognition and internalisation of intracellular pathogens by host cells is a multifactorial process, involving both stable and transient interactions. The plasticity of the host cell plasma membrane is fundamental in this infectious process. Here, the participation of macrophage lipid microdomains during adhesion and internalisation of the fungal pathogen Histoplasma capsulatum (Hc) was investigated. An increase in membrane lateral organisation, which is a characteristic of lipid microdomains, was observed during the first steps of Hc-macrophage interaction. Cholesterol enrichment in macrophage membranes around Hc contact regions and reduced levels of Hc-macrophage association after cholesterol removal also suggested the participation of lipid microdomains during Hc-macrophage interaction. Using optical tweezers to study cell-to-cell interactions, we showed that cholesterol depletion increased the time required for Hc adhesion. Additionally, fungal internalisation was significantly reduced under these conditions. Moreover, macrophages treated with the ceramide-glucosyltransferase inhibitor (P4r) and macrophages with altered ganglioside synthesis (from B4galnt1-/- mice) showed a deficient ability to interact with Hc. Coincubation of oligo-GM1 and treatment with Cholera toxin Subunit B, which recognises the ganglioside GM1, also reduced Hc association. Although purified GM1 did not alter Hc binding, treatment with P4 significantly increased the time required for Hc binding to macrophages. The content of CD18 was displaced from lipid microdomains in B4galnt1-/- macrophages. In addition, macrophages with reduced CD18 expression (CD18low ) were associated with Hc at levels similar to wild-type cells. Finally, CD11b and CD18 colocalised with GM1 during Hc-macrophage interaction. Our results indicate that lipid rafts and particularly complex gangliosides that reside in lipid rafts stabilise Hc-macrophage adhesion and mediate efficient internalisation during histoplasmosis.

A glucuronoxylomannan-like glycan produced by Trichosporon mucoides.

Trichosporon asahii shares with Cryptococcus species the ability to produce glucuronoxylomannan (GXM), an immunomodulatory fungal polysaccharide. The ability of other opportunistic species of Trichosporon to produce GXM-like polysaccharides is unknown. In this study, we observed that T. mucoides was less pathogenic than T. asahii in an infection model of Galleria mellonella and asked whether this difference was related to the characteristics of GXM-like molecules. Compositional analysis of samples obtained from both pathogens indicated that the components of GXM (mannose, xylose and glucuronic acid) were, in fact, detected in T. mucoides and T. asahii glycans. The identification of the T. mucoides glycan as a GXM-like molecule was confirmed by its reactivity with a monoclonal antibody raised to cryptococcal GXM and incorporation of the glycan into the cell surface of an acapsular mutant of C. neoformans. T. mucoides and T. asahii glycans differed in molecular dimensions. The antibody to cryptococcal GXM recognized T. mucoides yeast forms less efficiently than T. asahii cells. Experiments with animal cells revealed that the T. mucoides glycan manifested antiphagocytic properties. Comparative phagocytosis assays revealed that T. mucoides and T. asahii were similarly recognized by macrophages. However, fungal association with the phagocytes did not depend on the typical receptors of cryptococcal GXM, as concluded from assays using macrophages obtained from Tlr2-/- and Cd14-/- knockout mice. These results add T. mucoides to the list of fungal pathogens producing GXM-like glycans, but also indicate a high functional diversity of this major fungal immunogen.

Compositional and immunobiological analyses of extracellular vesicles released by Candida albicans.

The release of extracellular vesicles (EV) by fungal organisms is considered an alternative transport mechanism to trans-cell wall passage of macromolecules. Previous studies have revealed the presence of EV in culture supernatants from fungal pathogens, such as Cryptococcus neoformans, Histoplasma capsulatum, Paracoccidioides brasiliensis, Sporothrix schenckii, Malassezia sympodialis and Candida albicans. Here we investigated the size, composition, kinetics of internalization by bone marrow-derived murine macrophages (MO) and dendritic cells (DC), and the immunomodulatory activity of C. albicans EV. We also evaluated the impact of EV on fungal virulence using the Galleria mellonella larvae model. By transmission electron microscopy and dynamic light scattering, we identified two populations ranging from 50 to 100 nm and 350 to 850 nm. Two predominant seroreactive proteins (27 kDa and 37 kDa) and a group of polydispersed mannoproteins were observed in EV by immunoblotting analysis. Proteomic analysis of C. albicans EV revealed proteins related to pathogenesis, cell organization, carbohydrate and lipid metabolism, response to stress, and several other functions. The major lipids detected by thin-layer chromatography were ergosterol, lanosterol and glucosylceramide. Short exposure of MO to EV resulted in internalization of these vesicles and production of nitric oxide, interleukin (IL)-12, transforming growth factor-beta (TGF-ß) and IL-10. Similarly, EV-treated DC produced IL-12p40, IL-10 and tumour necrosis factor-alpha. In addition, EV treatment induced the up-regulation of CD86 and major histocompatibility complex class-II (MHC-II). Inoculation of G. mellonella larvae with EV followed by challenge with C. albicans reduced the number of recovered viable yeasts in comparison with infected larvae control. Taken together, our results demonstrate that C. albicans EV were immunologically active and could potentially interfere with the host responses in the setting of invasive candidiasis.

Antibody binding to Cryptococcus neoformans impairs budding by altering capsular mechanical properties.

Abs to microbial capsules are critical for host defense against encapsulated pathogens, but very little is known about the effects of Ab binding on the capsule, apart from producing qualitative capsular reactions ("quellung" effects). A problem in studying Ab-capsule interactions is the lack of experimental methodology, given that capsules are fragile, highly hydrated structures. In this study, we pioneered the use of optical tweezers microscopy to study Ab-capsule interactions. Binding of protective mAbs to the capsule of the fungal pathogen Cryptococcus neoformans impaired yeast budding by trapping newly emerging buds inside the parental capsule. This effect is due to profound mAb-mediated changes in capsular mechanical properties, demonstrated by a concentration-dependent increase in capsule stiffness. This increase involved mAb-mediated cross-linking of capsular polysaccharide molecules. These results provide new insights into Ab-mediated immunity, while suggesting a new nonclassical mechanism of Ab function, which may apply to other encapsulated pathogens. Our findings add to the growing body of evidence that Abs have direct antimicrobial functions independent of other components of the immune system.

Probiotic Saccharomyces cerevisiae strains as biotherapeutic tools: is there room for improvement?

The probiotic yeast Saccharomyces cerevisiae var boulardii is widely used as a low cost and efficient adjuvant against gastrointestinal tract disorders such as inflammatory bowel disease and treatment of several types of diarrhea, both in humans and animals. S. boulardii exerts its protective mechanisms by binding and neutralizing enteric pathogens or their toxins, by reducing inflammation and by inducing the secretion of sIgA. Although several S. cerevisiae strains have proven probiotic potential in both humans and animals, only S. boulardii is currently licensed for use in humans. Recently, some researchers started using S. boulardii as heterologous protein expression systems. Combined with their probiotic activity, the use of these strains as prophylactic and therapeutic proteins carriers might result in a positive combined effort to fight specific diseases. Here, we provide an overview of the current use of S. cerevisiae strains as probiotics and their mechanisms of action. We also discuss their potential to produce molecules with biotherapeutic application and the advantages and hurdles of this approach. Finally, we suggest future directions and alternatives for which the combined effort of specific immunomodulatory effects of probiotic S. cerevisiae strains and ability to express desired foreign genes would find a practical application.

Inhibition of Candida parapsilosis fatty acid synthase (Fas2) induces mitochondrial cell death in serum.

We have recently observed that a fatty acid auxotrophic mutant (fatty acid synthase, Fas2Δ/Δ) of the emerging human pathogenic yeast Candida parapsilosis dies after incubation in various media including serum. In the present study we describe the mechanism for cell death induced by serum and glucose containing media. We show that Fas2Δ/Δ yeast cells are profoundly susceptible to glucose leading us to propose that yeast cells lacking fatty acids exhibit uncontrolled metabolism in response to glucose. We demonstrate that incubation of Fas2Δ/Δ yeast cells with serum leads to cell death, and this process can be prevented with inhibition of protein or DNA synthesis, indicating that newly synthesized cellular components are detrimental to the mutant cells. Furthermore, we have found that cell death is mediated by mitochondria. Suppression of electron transport enzymes using inhibitors such as cyanide or azide prevents ROS overproduction and Fas2Δ/Δ yeast cell death. Additionally, deletion of mitochondrial DNA, which encodes several subunits for enzymes of the electron transport chain, significantly reduces serum-induced Fas2Δ/Δ yeast cell death. Therefore, our results show that serum and glucose media induce Fas2Δ/Δ yeast cell death by triggering unbalanced metabolism, which is regulated by mitochondria. To our knowledge, this is the first study to critically define a link between cytosolic fatty acid synthesis and mitochondrial function in response to serum stress in C. parapsilosis.

Morphological and pathogenic investigation of the emerging fungal threat Emergomyces africanus.

Emergomyces africanus is a highly fatal fungal pathogen affecting individuals with advanced HIV disease. Molecular patterns and ultrastructural aspects of E. africanus are unknown, and pathogenic models have not been investigated in detail. Since the cell wall of fungi is a determinant for interaction with the host and antifungal development, we characterized the ultrastructural aspects of E. africanus and the general properties of cell wall components under different conditions of growth in vitro and in vivo. We also tested the pathogenic potential of E. africanus in a Galleria mellonella model of infection. Transmission electron microscopy revealed the common intracellular, ultrastructural features of fungi in association with a thick cell wall. Scanning electron microscopy revealed a smooth cell surface, with no apparent decorative structures. Yeast cultures of E. africanus showed the distribution of chitin, chitooligomers, and mannoproteins commonly observed in fungi. However, in mixed microenvironments containing yeast and filamenting forms of E. africanus, the detection of chitooligomers was increased in comparison with isolated yeast cells, while the detection of these components in filamenting forms was markedly reduced. These observations were suggestive of the ability of E. africanus to change its cell wall composition in response to different microenvironments. Although E. africanus was unable to kill G. mellonella, this infection model allowed us to isolate infected hemocytes for further analysis of mannoproteins, chitin, and chitooligomers. Once again, the detection of E. africanus chitooligomers was markedly increased. These results reveal previously unknown ultrastructural features of E. africanus and suggest a high plasticity in the cell wall of this lethal pathogen. IMPORTANCE: The epidemiology of fungal infections is very dynamic, and novel health emergencies are hard to predict. New fungal pathogens have been continuously emerging for the last few decades, and Emergomyces africanus is one of these threats to human health. This complex scenario points to the need for generating knowledge about emerging pathogens so that new therapeutic strategies can be designed. In this study, we characterized the general cellular and pathogenic properties of the emerging fungal pathogen E. africanus. Our results reveal that E. africanus manifests some of the typical properties of fungal cells but also exhibits some unique characteristics that might be helpful for the future development of therapeutic strategies.

Alkaloids solenopsins from fire ants display in vitro and in vivo activity against the yeast Candida auris.

The urgency surrounding Candida auris as a public health threat is highlighted by both the Center for Disease Control (CDC) and World Health Organization (WHO) that categorized this species as priority fungal pathogen. Given the current limitations with antifungal therapy for C. auris, particularly due to its multiple resistance to the current antifungals, the identification of new drugs is of paramount importance. Some alkaloids abundant in the venom of the red invasive fire ant (Solenopsis invicta), known as solenopsins, have garnered attention as potent inhibitors of bacterial biofilms, and there are no studies demonstrating such effects against fungal pathogens. Thus, we herein investigated the antibiotic efficacy of solenopsin alkaloids against C. auris biofilms and planktonic cells. Both natural and synthetic solenopsins inhibited the growth of C. auris strains from different clades, including fluconazole and amphotericin B-resistant isolates. Such alkaloids also inhibited matrix deposition and altered cellular metabolic activity of C. auris in biofilm conditions. Mechanistically, the alkaloids compromised membrane integrity as measured by propidium iodide uptake in exposed planktonic cells. Additionally, combining the alkaloids with AMB yielded an additive antifungal effect, even against AMB-resistant strains. Finally, both extracted solenopsins and the synthetic analogues demonstrated protective effect in vivo against C. auris infection in the invertebrate model Galleria mellonella. These findings underscore the potent antifungal activities of solenopsins against C. auris and suggest their inclusion in future drug development. Furthermore, exploring derivatives of solenopsins could reveal novel compounds with therapeutic promise.