Phosphomannosylation and the Functional Analysis of the Extended Candida albicans MNN4-Like Gene Family

Sporothrix brasiliensis Gp70 is a cell wall protein required for adhesion, proper interaction with innate immune cells, and virulence

Sporothrix brasiliensis is one of the leading etiological agents of sporotrichosis, a cutaneous and subcutaneous mycosis worldwide distributed. This organism has been recently associated with epidemic outbreaks in Brazil. Despite the medical relevance of this species, little is known about its virulence factors, and most of the information on this subject is extrapolated from Sporothrix schenckii. Here, we generated S. brasiliensis mutants, where GP70 was silenced. In S. schenckii, this gene encodes a glycoprotein with adhesive properties required for virulence. The S. brasiliensis GP70 silencing led to an abnormal cellular phenotype, with smaller, round yeast-like cells that aggregate. Cell aggregation was disrupted with glucanase, suggesting this phenotype is linked to changes in the cell wall. The cell wall characterization confirmed changes in the structural polysaccharide β-1,3-glucan, which increased in quantity and exposure at the cell surface. This was accompanied by a reduction in protein content and N-linked glycans. Mutant strains with high GP70-silencing levels showed minimal levels of 3-carboxy-cis,cis-muconate cyclase activity, this glycoprotein's predicted enzyme function, and decreased ability to bind laminin and fibronectin. These phenotypical changes coincided with abnormal interaction with human peripheral blood mononuclear cells, where production of IL-1β, IL-17, and IL-22 was reduced and the strong dependence on cytokine stimulation via mannose receptor was lost. Phagocytosis by monocyte-derived macrophages was increased and virulence attenuated in a Galleria mellonella larvae. In conclusion, Gp70 is an abundant cell wall glycoprotein in S. brasiliensis that contributes to virulence and proper interaction with innate immnune cells.

The sunflower jacalin Helja: biological and structural insights of its antifungal activity against Candida albicans

The limited availability of efficient treatments for Candida infections and the increased emergence of antifungal-resistant strains stimulates the search for new antifungal agents. We have previously isolated a sunflower mannose-binding lectin (Helja) with antifungal activity against Candida albicans, capable of binding mannose-bearing oligosaccharides exposed on the cell surface. This work aimed to investigate the biological and biophysical basis of Helja's binding to C. albicans cell wall mannans and its influence on the fungicidal activity of the lectin. We evaluated the interaction of Helja with the cell wall mannans extracted from the isogenic parental strain (WT) and a glycosylation-defective C. albicans with altered cell wall phosphomannosylation (mnn4∆ null mutants) and investigated its antifungal effect. Helja exhibited stronger antifungal activity on the mutant strain, showing greater inhibition of fungal growth, loss of cell viability, morphological alteration, and formation of clusters with agglutinated cells. This differential biological activity of Helja was correlated with the biophysical parameters determined by solid phase assays and isothermal titration calorimetry, which demonstrated that the lectin established stronger interactions with the cell wall mannans of the mnn4∆ null mutant than with the WT strain. In conclusion, our results provide new evidence on the nature of the Helja molecular interactions with cell wall components, i.e. phosphomannan, and its impact on the antifungal activity. This study highlights the relevance of plant lectins in the design of effective antifungal therapies.

Differential Recognition of Clinically Relevant Sporothrix Species by Human Granulocytes

Sporotrichosis is a cutaneous mycosis that affects humans and animals and has a worldwide distribution. This infection is mainly caused by Sporothrix schenckii, Sporothrix brasiliensis, and Sporothrix globosa. Current research about anti-Sporothrix immunity has been mainly focused on S. schenckii and S. brasiliensis, using different types of human or animal immune cells. Granulocytes are a group of cells relevant for cytokine production, with the capacity for phagocytosis and the generation of neutrophil extracellular traps (NETs). Considering their importance, this study aimed to compare the capacity of human granulocytes to stimulate cytokines, uptake, and form NETs when interacting with different Sporothrix species. We found that conidia, germlings, and yeast-like cells from S. schenckii, S. brasiliensis, and S. globosa play an important role in the interaction with these immune cells, establishing morphology- and species-specific cytokine profiles. S. brasil-iensis tended to stimulate an anti-inflammatory cytokine profile, whilst the other two species had a proinflammatory one. S. globosa cells were the most phagocytosed cells, which occurred through a dectin-1-dependent mechanism, while the uptake of S. brasiliensis mainly occurred via TLR4 and CR3. Cell wall N-linked and O-linked glycans, along with β-1,3-glucan, played a significant role in the interaction of these Sporothrix species with human granulocytes. Finally, this study indicates that conidia and yeast-like cells are capable of inducing NETs, with the latter being a better stimulant. To the best of our knowledge, this is the first study that reports the cytokine profiles produced by human granulocytes interacting with Sporothrix cells.

Differential Recognition of Sporothrix schenckii, Sporothrix brasiliensis, and Sporothrix globosa by Human Monocyte-Derived Macrophages and Dendritic Cells

Background

Sporotrichosis is a mycosis frequently caused by Sporothrix schenckii, Sporothrix brasiliensis, and Sporothrix globosa. The cell wall is a species-specific fungal structure with a direct role in activating the host's immune response. The current knowledge about anti-Sporothrix immunity comes from studies using S. schenckii or S. brasiliensis and murine cells. Macrophages and dendritic cells detect and eliminate pathogens, and although the function of these cells links innate with adaptive immunity, little is known about their interaction with Sporothrix spp.

Methods

S. schenckii, S. brasiliensis, and S. globosa conidia or yeast-like cells were co-incubated with human monocyte-derived macrophages or dendritic cells, and the phagocytosis and cytokine stimulation were assessed. These interactions were also performed in the presence of specific blocking agents of immune receptors or fungal cells with altered walls to analyze the contribution of these molecules to the immune cell-fungus interaction.

Results

Both types of immune cells phagocytosed S. globosa conidia and yeast-like cells to a greater extent, followed by S. brasiliensis and S. schenckii. Furthermore, when the wall internal components were exposed, the phagocytosis level increased for S. schenckii and S. brasiliensis, in contrast to S. globosa. Thus, the cell wall components have different functions during the interaction with macrophages and dendritic cells. S. globosa stimulated an increased proinflammatory response when compared to the other species. In macrophages, this was a dectin-1-, mannose receptor-, and TLR2-dependent response, but dectin-1- and TLR2-dependent stimulation in dendritic cells. For S. schenckii and S. brasiliensis, cytokine production was dependent on the activation of TLR4, CR3, and DC-SIGN.

Conclusion

The results of this study indicate that these species are recognized by immune cells differently and that this may depend on both the structure and cell wall organization of the different morphologies.

Synergistic Antifungal Interactions between Antibiotic Amphotericin B and Selected 1,3,4-thiadiazole Derivatives, Determined by Microbiological, Cytochemical, and Molecular Spectroscopic Studies

In recent years, drug-resistant and multidrug-resistant fungal strains have been more frequently isolated in clinical practice. This phenomenon is responsible for difficulties in the treatment of infections. Therefore, the development of new antifungal drugs is an extremely important challenge. Combinations of selected 1,3,4-thiadiazole derivatives with amphotericin B showing strong synergic antifungal interactions are promising candidates for such formulas. In the study, microbiological, cytochemical, and molecular spectroscopy methods were used to investigate the antifungal synergy mechanisms associated with the aforementioned combinations. The present results indicate that two derivatives, i.e., C1 and NTBD, demonstrate strong synergistic interactions with AmB against some Candida species. The ATR-FTIR analysis showed that yeasts treated with the C1 + AmB and NTBD + AmB compositions, compared with those treated with single compounds, exhibited more pronounced abnormalities in the biomolecular content, suggesting that the main mechanism of the synergistic antifungal activity of the compounds is related to a disturbance in cell wall integrity. The analysis of the electron absorption and fluorescence spectra revealed that the biophysical mechanism underlying the observed synergy is associated with disaggregation of AmB molecules induced by the 1,3,4-thiadiazole derivatives. Such observations suggest the possibility of the successful application of thiadiazole derivatives combined with AmB in the therapy of fungal infections.

Non-albicans Candida Species: Immune Response, Evasion Mechanisms, and New Plant-Derived Alternative Therapies

Fungal infections caused by Candida species have become a constant threat to public health, especially for immunocompromised patients, who are considered susceptible to this type of opportunistic infections. Candida albicans is known as the most common etiological agent of candidiasis; however, other species, such as Candida tropicalis, Candida parapsilosis, Nakaseomyces glabrata (previously known as Candida glabrata), Candida auris, Candida guilliermondii, and Pichia kudriavzevii (previously named as Candida krusei), have also gained great importance in recent years. The increasing frequency of the isolation of this non-albicans Candida species is associated with different factors, such as constant exposure to antifungal drugs, the use of catheters in hospitalized patients, cancer, age, and geographic distribution. The main concerns for the control of these pathogens include their ability to evade the mechanisms of action of different drugs, thus developing resistance to antifungal drugs, and it has also been shown that some of these species also manage to evade the host's immunity. These biological traits make candidiasis treatment a challenging task. In this review manuscript, a detailed update of the recent literature on the six most relevant non-albicans Candida species is provided, focusing on the immune response, evasion mechanisms, and new plant-derived compounds with antifungal properties.

Silencing of ROT2, the Encoding Gene of the Endoplasmic Reticulum Glucosidase II, Affects the Cell Wall and the Sporothrix schenckii-Host Interaction

Sporothrix schenckii is a member of the Sporothrix pathogenic clade and one of the most common etiological agents of sporotrichosis, a subcutaneous fungal infection that affects both animal and human beings. Like other fungal pathogens, the Sporothrix cell wall is composed of structural polysaccharides and glycoproteins that are covalently modified with both N-linked and O-linked glycans. Thus far, little is known about the N-linked glycosylation pathway in this organism or its contribution to cell wall composition and interaction with the host. Here, we silenced ROT2, which encodes the catalytic subunit of the endoplasmic reticulum α-glucosidase II, a processing enzyme key for the N-linked glycan core processing. Silencing of ROT2 led to the accumulation of the Glc₂Man₉GlcNAC₂ glycan core at the cell wall and a reduction in the total content of N-linked glycans found in the wall. However, the highly silenced mutants showed a compensatory mechanism with increased content of cell wall O-linked glycans. The phenotype of mutants with intermediate levels of ROT2 silencing was more informative, as they showed changes in the cell wall composition and exposure of β-1.3-glucans and chitin at the cell surface. Furthermore, the ability to stimulate cytokine production by human mononuclear cells was affected, along with the phagocytosis by human monocyte-derived macrophages, in a mannose receptor-, complement receptor 3-, and TLR4-dependent stimulation. In an insect model of experimental sporotrichosis, these mutant cells showed virulence attenuation. In conclusion, S. schenckii ROT2 is required for proper N-linked glycosylation, cell wall organization and composition, and interaction with the host.

Current Models to Study the Sporothrix-Host Interaction

Sporotrichosis is a worldwide distributed subcutaneous mycosis that affects mammals, including human beings. The infection is caused by members of the Sporothrix pathogenic clade, which includes Sporothrix schenckii, Sporothrix brasiliensis, and Sporothrix globosa. The fungus can be acquired through traumatic inoculation of conidia growing in vegetal debris or by zoonotic transmission from sick animals. Although is not considered a life-threatening disease, it is an emergent health problem that affects mostly immunocompromised patients. The sporotrichosis causative agents differ in their virulence, host range, and sensitivity to antifungal drugs; therefore, it is relevant to understand the molecular bases of their pathogenesis, interaction with immune effectors, and mechanisms to acquired resistance to antifungal compounds. Murine models are considered the gold standard to address these questions; however, some alternative hosts offer numerous advantages over mammalian models, such as invertebrates like Galleria mellonella and Tenebrio molitor, or ex vivo models, which are useful tools to approach questions beyond virulence, without the ethical or budgetary features associated with the use of animal models. In this review, we analyze the different models currently used to study the host-Sporothrix interaction.

Disruption of protein rhamnosylation affects the Sporothrix schenckii-host interaction

Sporotrichosis is a fungal disease caused by the members of the Sporothrix pathogenic clade, and one of the etiological agents is Sporothrix schenckii. The cell wall of this organism has been previously analyzed and thus far is known to contain an inner layer composed of chitin and β -glucans, and an outer layer of glycoproteins, which are decorated with mannose and rhamnose-containing oligosaccharides. The L-rhamnose biosynthesis pathway is common in bacteria but rare in members of the Fungi kingdom. Therefore, in this study, we aimed to disrupt this metabolic route to assess the contribution of rhamnose during the S. schenckii-host interaction. We identified and silenced in S. schenckii a functional ortholog of the bacterial rmlD gene, which encodes for an essential reductase for the synthesis of nucleotide-activated L-rhamnose. RmlD silencing did not affect fungal growth or morphology but decreased cell wall rhamnose content. Compensatory, the β-1,3-glucan levels increased and were more exposed at the cell surface. Moreover, when incubated with human peripheral blood mononuclear cells, the RmlD silenced mutants differentially stimulated cytokine production when compared with the wild-type strain, reducing TNFα and IL-6 levels and increasing IL-1 β and IL-10 production. Upon incubation with human monocyte-derived macrophages, the silenced strains were more efficiently phagocytosed than the wild-type strain. In both cases, our data suggest that rhamnose-based oligosaccharides are ligands that interact with TLR4. Finally, our findings showed that cell wall rhamnose is required for the S. schenckii virulence in the G. mellonella model of infection.

Ceragenin-Coated Non-Spherical Gold Nanoparticles as Novel Candidacidal Agents

BACKGROUND

Infections caused by Candida spp. have become one of the major causes of morbidity and mortality in immunocompromised patients. Therefore, new effective fungicides are urgently needed, especially due to an escalating resistance crisis.

METHODS

A set of nanosystems with rod- (AuR), peanut- (AuP), and star-shaped (AuS) metal cores were synthesized. These gold nanoparticles were conjugated with ceragenins CSA-13, CSA-44, and CSA-131, and their activity was evaluated against Candida strains (n = 21) through the assessment of MICs (minimum inhibitory concentrations)/MFCs (minimum fungicidal concentrations). Moreover, in order to determine the potential for resistance development, serial passages of Candida cells with tested nanosystems were performed. The principal mechanism of action of Au NPs was evaluated via ROS (reactive oxygen species) generation assessment, plasma membrane permeabilization, and release of the protein content. Finally, to evaluate the potential toxicity of Au NPs, the measurement of hemoglobin release from red blood cells (RBCs) was carried out.

RESULTS

All of the tested nanosystems exerted a potent candidacidal activity, regardless of the species or susceptibility to other antifungal agents. Significantly, no resistance development after 25 passages of Candida cells with AuR@CSA-13, AuR@CSA-44, and AuR@CSA-131 nanosystems was observed. Moreover, the fungicidal mechanism of action of the investigated nanosystems involved the generation of ROS, damage of the fungal cell membrane, and leakage of intracellular contents. Notably, no significant RBCs hemolysis at candidacidal doses of tested nanosystems was detected.

CONCLUSIONS

The results provide rationale for the development of gold nanoparticles of rod-, peanut-, and star-shaped conjugated with CSA-13, CSA-44, and CSA-131 as effective candidacidal agents.

CRISPR-Based Genetic Manipulation of Candida Species: Historical Perspectives and Current Approaches

The Candida genus encompasses a diverse group of ascomycete fungi that have captured the attention of the scientific community, due to both their role in pathogenesis and emerging applications in biotechnology; the development of gene editing tools such as CRISPR, to analyze fungal genetics and perform functional genomic studies in these organisms, is essential to fully understand and exploit this genus, to further advance antifungal drug discovery and industrial value. However, genetic manipulation of Candida species has been met with several distinctive barriers to progress, such as unconventional codon usage in some species, as well as the absence of a complete sexual cycle in its diploid members. Despite these challenges, the last few decades have witnessed an expansion of the Candida genetic toolbox, allowing for diverse genome editing applications that range from introducing a single point mutation to generating large-scale mutant libraries for functional genomic studies. Clustered regularly interspaced short palindromic repeats (CRISPR)-Cas9 technology is among the most recent of these advancements, bringing unparalleled versatility and precision to genetic manipulation of Candida species. Since its initial applications in Candida albicans, CRISPR-Cas9 platforms are rapidly evolving to permit efficient gene editing in other members of the genus. The technology has proven useful in elucidating the pathogenesis and host-pathogen interactions of medically relevant Candida species, and has led to novel insights on antifungal drug susceptibility and resistance, as well as innovative treatment strategies. CRISPR-Cas9 tools have also been exploited to uncover potential applications of Candida species in industrial contexts. This review is intended to provide a historical overview of genetic approaches used to study the Candida genus and to discuss the state of the art of CRISPR-based genetic manipulation of Candida species, highlighting its contributions to deciphering the biology of this genus, as well as providing perspectives for the future of Candida genetics.

Role of Protein Glycosylation in Interactions of Medically Relevant Fungi with the Host

Protein glycosylation is a highly conserved post-translational modification among organisms. It plays fundamental roles in many biological processes, ranging from protein trafficking and cell adhesion to host–pathogen interactions. According to the amino acid side chain atoms to which glycans are linked, protein glycosylation can be divided into two major categories: N-glycosylation and O-glycosylation. However, there are other types of modifications such as the addition of GPI to the C-terminal end of the protein. Besides the importance of glycoproteins in biological functions, they are a major component of the fungal cell wall and plasma membrane and contribute to pathogenicity, virulence, and recognition by the host immunity. Given that this structure is absent in host mammalian cells, it stands as an attractive target for developing selective compounds for the treatment of fungal infections. This review focuses on describing the relationship between protein glycosylation and the host–immune interaction in medically relevant fungal species.

Revisiting the Vital Drivers and Mechanisms of β-Glucan Masking in Human Fungal Pathogen, Candida albicans

Among the several human fungal pathogens, Candida genus represents one of the most implicated in the clinical scenario. There exist several distinctive features that govern the establishment of Candida infections in addition to their capacity to adapt to multiple stress conditions inside humans which also include evasion of host immune responses. The complex fungal cell wall of the prevalent pathogen, Candida albicans, is one of the main targets of antifungal drugs and recognized by host immune cells. The wall consists of tiered arrangement of an outer thin but dense covering of mannan and inner buried layers of β-glucan and chitin. However, the pathogenic fungi adopt strategies to evade immune recognition by masking these molecules. This capacity to camouflage the immunogenic polysaccharide β-glucan from the host is a key virulence factor of C. albicans. The present review is an attempt to collate various underlying factors and mechanisms involved in Candida β-glucan masking from the available pool of knowledge and provide a comprehensive understanding. This will further improve therapeutic approaches to candidiasis by identifying new antifungal targets that blocks fungal immune evasion.

Tenebrio molitor as an Alternative Model to Analyze the Sporothrix Species Virulence

Background

Sporotrichosis is an increasing threat for humans, affecting mainly skin and subcutaneous tissues but that can cause disseminated infection in immunocompromised patients. Sporothrix schenckii, Sporothrix brasiliensis, and Sporothrix globosa are the main etiological agents of this mycosis, and each species show different virulence levels. The gold standard to assess fungal virulence is the mouse model that is expensive and time-consuming. Thus, invertebrate models have been reported as an alternative for the evaluation of fungal virulence. Here, we assessed whether Tenebrio molitor larvae could be a new alternative to study Sporothrix spp. virulence.

Methods

T. molitor larvae were inoculated with different doses of S. schenckii, S. brasiliensis, and S. globosa, and animal mortality, cytotoxicity, and immunological parameters were analyzed, including the ability to stimulate immunological priming.

Results

Mortality curves demonstrated that yeast-like cells were the best fungal morphology to kill larvae and showed a similar ranking in virulence than that reported in other animal models, ie, being S. brasiliensis and S. globosa the species with the highest and lowest virulence, respectively. The usefulness of this model was validated with the analysis of several S. schenckii strains with different virulence degrees, and changes in cytotoxicity, humoral and cellular immunological parameters. Low-virulence strains stimulated low levels of cytotoxicity, phenoloxidase activity, and hemocyte countings, and these immunological cells poorly uptake fungi. Moreover, using recombinant Gp70 from S. schenckii immunological priming was stimulated in larvae and this protected against a lethal dose of fungal cells from any of the three species under study.

Conclusion

The study demonstrated that T. molitor larvae are an appropriate alternative invertebrate model to analyze the virulence of S. schenckii, S. brasiliensis, and S. globosa. Additionally, hemocyte levels, phenoloxidase activity, cytotoxicity, uptake by hemocytes, and immunological priming are biological parameters that can be used to study the Sporothrix-T. molitor interaction.

Virulence Factors in Sporothrix schenckii, One of the Causative Agents of Sporotrichosis

Sporothrix schenckii is one of the etiological agents of sporotrichosis, a fungal infection distributed worldwide. Both, the causative organism and the disease have currently received limited attention by the medical mycology community, most likely because of the low mortality rates associated with it. Nonetheless, morbidity is high in endemic regions and the versatility of S. schenckii to cause zoonosis and sapronosis has attracted attention. Thus far, virulence factors associated with this organism are poorly described. Here, comparing the S. schenckii genome sequence with other medically relevant fungi, genes involved in morphological change, cell wall synthesis, immune evasion, thermotolerance, adhesion, biofilm formation, melanin production, nutrient uptake, response to stress, extracellular vesicle formation, and toxin production are predicted and discussed as putative virulence factors in S. schenckii.

Influences of the Culturing Media in the Virulence and Cell Wall of Sporothrix schenckii, Sporothrix brasiliensis, and Sporothrix globosa

Sporothrix schenckii, Sporothrix brasiliensis, and Sporothrix globosa are etiological agents of sporotrichosis, a human subcutaneous mycosis. Although the protocols to evaluate Sporothrix virulence in animal models are well described, the cell preparation before inoculation is not standardized, and several culturing media are used to grow yeast-like cells. Here, we found that carbon or nitrogen limitation during fungal cell preparation negatively impacted the ability of S. schenckii and S. brasiliensis to kill Galleria mellonella larvae, but not S. globosa. The fungal growth conditions associated with the short median survival of animals were accompanied by increased hemocyte countings, phenoloxidase activity, and cytotoxicity. The fungal growth under carbon or nitrogen limitation also affected the cell wall composition of both S. schenckii and S. brasiliensis and showed increased exposure of β-1,3-glucan at the cell surface, while those growing conditions had a minimal impact on the S.globosa wall, which had higher levels of this polysaccharide exposed on the wall regardless of the culture condition. This polysaccharide exposure was linked to the increased ability of insect hemocytes to uptake fungal cells, suggesting that this is one of the mechanisms behind the lower virulence of S.globosa or cells from the other species grown in carbon or nitrogen limitation.

Advances in Molecular Tools and In Vivo Models for the Study of Human Fungal Pathogenesis

Pathogenic fungi represent an increasing infectious disease threat to humans, especially with an increasing challenge of antifungal drug resistance. Over the decades, numerous tools have been developed to expedite the study of pathogenicity, initiation of disease, drug resistance and host-pathogen interactions. In this review, we highlight advances that have been made in the use of molecular tools using CRISPR technologies, RNA interference and transposon targeted mutagenesis. We also discuss the use of animal models in modelling disease of human fungal pathogens, focusing on zebrafish, the silkworm, Galleria mellonella and the murine model.

Loss of Kex2 Affects the Candida albicans Cell Wall and Interaction with Innate Immune Cells

The secretory pathway in Candida albicans involves the protein translocation into the lumen of the endoplasmic reticulum and transport to the Golgi complex, where proteins undergo posttranslational modifications, including glycosylation and proteolysis. The Golgi-resident Kex2 protease is involved in such processing and disruption of its encoding gene affected virulence and dimorphism. These previous studies were performed using cells without URA3 or with URA3 ectopically placed into the KEX2 locus. Since these conditions are known to affect the cellular fitness and the host-fungus interaction, here we generated a kex2Δ null mutant strain with URA3 placed into the neutral locus RPS1. The characterization of this strain showed defects in the cell wall composition, with a reduction in the N-linked mannan content, and the increment in the levels of O-linked mannans, chitin, and β-glucans. The defects in the mannan content are likely linked to changes in Golgi-resident enzymes, as the α-1,2-mannosyltransferase and α-1,6-mannosyltransferase activities were incremented and reduced, respectively. The mutant cells also showed reduced ability to stimulate cytokine production and phagocytosis by human mononuclear cells and macrophages, respectively. Collectively, these data showed that loss of Kex2 affected the cell wall composition, the protein glycosylation pathways, and interaction with innate immune cells.

Antifungal Activity of Anionic Defense Peptides: Insight into the Action of Galleria mellonella Anionic Peptide 2

Anionic antimicrobial peptides constitute an integral component of animal innate immunity, however the mechanisms of their antifungal activity are still poorly understood. The action of a unique Galleria mellonella anionic peptide 2 (AP2) against fungal pathogen Candida albicans was examined using different microscopic techniques and Fourier transform infrared (FTIR) spectroscopy. Although the exposure to AP2 decreased the survival rate of C. albicans cells, the viability of protoplasts was not affected, suggesting an important role of the fungal cell wall in the peptide action. Atomic force microscopy showed that the AP2-treated cells became decorated with numerous small clods and exhibited increased adhesion forces. Intensified lomasome formation, vacuolization, and partial distortion of the cell wall was also observed. FTIR spectroscopy suggested AP2 interactions with the cell surface proteins, leading to destabilization of protein secondary structures. Regardless of the anionic character of the whole AP2 molecule, bioinformatics analyses revealed the presence of amphipathic α-helices with exposed positively charged lysine residues. High content of the α-helical structure was confirmed after deconvolution of the IR absorption spectrum and during circular dichroism measurements. Our results indicated that the antimicrobial properties of G. mellonella AP2 rely on the same general characteristics found in cationic defense peptides.

Differential recognition of Candida tropicalis, Candida guilliermondii, Candida krusei, and Candida auris by human innate immune cells

Background

The deep-seated infections caused by the Candida genus are associated with a high mortality rate, and Candida albicans is the most frequent species associated with these diseases. The fungal wall is composed of macromolecules not synthesized by the host, and therefore is a source of ligands recognized by innate immune cells.

Methods

We performed a comparative study analyzing the cell wall composition and organization of Candida tropicalis, Candida guilliermondii, Candida krusei, and Candida auris, along with their ability to stimulate cytokine production and phagocytosis by human innate immune cells.

Results

We found that the wall of these species had the basic components already described in C. albicans, with most of the chitin and b1,3-glucan located underneath the mannan layer. However, the walls of C. krusei and C. auris were rich in chitin and the former had a lower content of mannans. C. guilliermondii contained changes in the mannan and the b1,3-glucan levels. These species were differentially phagocytosed by human macrophages and stimulated cytokine production in a dectin-1-dependent pathway. C. krusei showed the most significant changes in the tested parameters, whereas C. auris behaved like C. albicans.

Conclusion

Our results suggest that the cell wall and innate immune recognition of C. tropicalis, C. guilliermondii, C. krusei, and Candida auris is different from that reported for C. albicans.

Role of protein phosphomannosylation in the Candida tropicalis-macrophage interaction

Candida tropicalis is an opportunistic fungal pathogen responsible for mucosal and systemic infections. The cell wall is the initial contact point between a fungal cell and the host immune system, and mannoproteins are important components that play key roles when interacting with host cells. In Candida albicans, mannans are modified by mannosyl-phosphate moieties, named phosphomannans, which can work as molecular scaffolds to synthesize β1,2-mannooligosaccharides, and MNN4 is a positive regulator of the phosphomannosylation pathway. Here, we showed that C. tropicalis also displays phosphomannans on the cell surface, but the amount of this cell wall component varies depending on the fungal strain. We also identified a functional ortholog of CaMNN4 in C. tropicalis. Disruption of this gene caused depletion of phosphomannan content. The C. tropicalis mnn4Δ did not show defects in the ability to stimulate cytokine production by human mononuclear cells but displayed virulence attenuation in an insect model of candidiasis. When the mnn4Δ-macrophage interaction was analyzed, results showed that presence of cell wall phosphomannan was critical for C. tropicalis phagocytosis. Finally, our results strongly suggest a differential role for phosphomannans during phagocytosis of C. albicans and C. tropicalis.

Silencing of OCH1 unveils the role of Sporothrix schenckii N-linked glycans during the host-fungus interaction

BACKGROUND

Sporothrix schenckii is a neglected fungal pathogen for the human being and other mammals. In several fungal systems, Och1 is a Golgi α1,6-mannosyltransferase with a key function in the synthesis of N-linked glycans; which are important elements during the host-fungus interplay. The role of OCH1 in fungal virulence seems to be species-specific, being an essential component for Candida albicans virulence and dispensable during the interaction of Aspergillus fumigatus with the host.

METHODS

Here, we silenced S. schenckii OCH1 and characterized the phenotype of the mutant strains.

RESULTS

The mutant strains did not show defects in the cell or colony morphology, the growth rate or the ability to undergo dimorphism; but the cell wall changed in both composition and exposure of inner components at the surface. When interacting with human monocytes, the silenced strains had a reduced ability to stimulate TNFα and IL-6 but stimulated higher levels of IL-10. The interaction with human macrophages was also altered, with reduced numbers of silenced cells phagocytosed. These strains showed virulence attenuation in both Galleria mellonella and in the mouse model of sporotrichosis. Nonetheless, the cytokine levels in infected organs did not vary significantly when compared with the wild-type strain.

CONCLUSION

Our data demonstrate that OCH1 silencing affects different aspects of the S. schenckii-host interaction.

Generation of Sporothrix schenckii mutants expressing the green fluorescent protein suitable for the study of host-fungus interactions

Sporotrichosis is an infection caused by members of the Sporothrix genus, and among them, Sporothrix schenckii is one of the etiological agents. Both, the disease and the causative agent have gained interest in the recent years, because of the report of epidemic outbreaks, and the description of the disease transmission from animals to human beings. Despite the relevance of S. schenckii in the clinical field, there are basic aspects of its biology poorly explored. So far, Agrobacterium tumefaciens-mediated transformation has been reported as an alternative for genetic manipulation of this fungal pathogen. Here, we report the optimization of the transformation method and used this to generate insertional mutants that express the green fluorescent protein in S. schenckii. We obtained five mutant strains that showed mitotic stability and expression of the reporter gene. The strains displayed normal cell wall composition, and a similar ability to interact ex vivo with human monocytes and monocyte-derived macrophages. Moreover, the virulence in larvae of Galleria mellonella was similar to that obtained with the wild-type control strains. These data indicate that these fluorescent mutants with normal ability to interact with the host could be used in bioimaging to track the host-Sporothrix interaction in vivo.