Fungal Pathogens: Shape-Shifting Invaders

Deciphering Aspergillus section Terrei in Galleria mellonella model: a clade-specific pathogenicity characterization

The Aspergillus genus encompasses a diverse array of species, some of which are opportunistic pathogens. Traditionally, human aspergillosis has primarily been linked to a few Aspergillus species, predominantly A. fumigatus. Changes in epidemiology and advancements in molecular techniques have brought attention to less common and previously unrecognized pathogenic cryptic species. Despite the taxonomic recognition of many cryptic species in section Terrei, their virulence potential and clinical implications, compared to A. terreus sensu stricto, remain poorly understood. Hence, the current study utilized the alternative in vivo model Galleria mellonella to evaluate the virulence potential of 19 accepted Aspergillus species in section Terrei, classified into three series (major phylogenetic clades): Terrei, Nivei, and Ambigui. Analyzing the median survival rates of infected larvae of all species in each series revealed that series Ambigui has a significantly lower virulence compared to series Terrei and Nivei. Taking a closer look at series Terrei and Nivei revealed a trend of survival within each clade, dividing the species into two groups: highly virulent (up to 72 h survival) and less virulent (up to 144 h survival). Histological observation, considering fungal distribution and filamentation, further supported this assessment, revealing increased distribution and hyphal formation in virulent species. Additionally, the susceptibility profile of conventional antifungals was determined, revealing an increased azole minimum inhibitory concentration for some tested cryptic species such as A. niveus and A. iranicus. Our results highlight the importance of cryptic species identification, as they can exhibit different levels of virulence and show reduced antifungal susceptibility.

IMPORTANCE

With changing fungal epidemiology and an increasingly vulnerable population, cryptic Aspergillus species are emerging as human pathogens. Their diversity and clinical relevance remain underexplored, with some species showing reduced antifungal susceptibility and higher virulence, highlighting the need for better preparedness in clinical practice. Using the Galleria mellonella model, we assessed the virulence of Aspergillus species of section Terrei, including cryptic and non-cryptic species, across three series Terrei, Nivei, and Ambigui. The results revealed significant virulence variation among the series, with some cryptic species displaying high virulence. Histological analysis confirmed increased hyphal formation and fungal spread in the more virulent species. Additionally, elevated azole minimum inhibitory concentrations were also observed in certain cryptic species. This study presents novel insights into the pathogenicity of Aspergillus section Terrei, emphasizing the critical importance of accurately identifying cryptic species due to their diverse virulence potential and antifungal resistance, which may have substantial clinical implications.

Shape-Shifting Mechanisms: Integrative Multi-Omics Insights Into Candida albicans Morphogenesis

The ability of Candida albicans to switch among yeast, hyphal, and pseudohyphal forms underlies its adaptability and pathogenicity. While cAMP-dependent signaling has long been considered central to hyphal growth, recent multi-omics studies show that cAMP-independent mechanisms also drive morphological changes. Basal PKA activity, cyclin-dependent kinases (e.g., Cdc28), and other regulators can promote shape-shifting even without classical cAMP pathways. In addition, N-acetylglucosamine (GlcNAc) acts as a potent signal that induces hyphal growth independently of its metabolic role, directly connecting environmental cues to morphological states. By integrating transcriptomic, proteomic, and phosphoproteomic data, this review exposes the intricate networks controlling C. albicans morphogenesis. A clearer understanding of these complex regulatory circuits lays the groundwork for future studies that employ advanced multi-omics analyses. Such approaches will help elucidate how these pathways converge, how they respond to changing environments, and how they might be harnessed or disrupted to influence fungal behavior.

Regulation of yeast polarized exocytosis by phosphoinositide lipids

Phosphoinositides help steer membrane trafficking routes within eukaryotic cells. In polarized exocytosis, which targets vesicular cargo to sites of polarized growth at the plasma membrane (PM), the two phosphoinositides phosphatidylinositol 4-phosphate (PI4P) and its derivative phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) pave the pathway for vesicle transport from the Golgi to the PM. PI4P is a critical regulator of mechanisms that shape late Golgi membranes for vesicle biogenesis and release. Although enriched in vesicle membranes, PI4P is inexplicably removed from post-Golgi vesicles during their transit to the PM, which drives subsequent steps in exocytosis. At the PM, PI(4,5)P2 recruits effectors that establish polarized membrane sites for targeting the vesicular delivery of secretory cargo. The budding yeast Saccharomyces cerevisiae provides an elegant model to unravel the complexities of phosphoinositide regulation during polarized exocytosis. Here, we review how PI4P and PI(4,5)P2 promote yeast vesicle biogenesis, exocyst complex assembly and vesicle docking at polarized cortical sites, and suggest how these steps might impact related mechanisms of human disease.

Candida species in periodontitis: A new villain or a new target?

OBJECTIVES

Recent research indicated that fungi might have a role in periodontitis alongside traditional periodontal pathogens. This state-of-the-art narrative review explores current concepts on the involvement of Candida species in periodontitis, and suggests the potential for ecological management of this disease.

DATA, SOURCES AND STUDY SELECTION

A literature search was conducted for a narrative review on Web of Science, PubMed, Medline and Scopus about periodontitis associated with Candida species. Published articles, including case reports, case series, observational and interventional clinical trials, and critical appraisals of the literature were retrieved and reviewed.

CONCLUSIONS

Several factors predispose individuals to periodontitis associated with Candida species. These include systemic diseases that lead to immunosuppression and oral environment changes such as cigarette smoking. While a consistent significant increase in the detection rate of Candida species in patients with periodontitis has not been universally observed, there is evidence linking Candida species to the severity of periodontitis and their potential to worsen the condition. Candida species may participate in the development of periodontitis in various ways, including cross-kingdom interactions with periodontal pathogens, changes in the local or systemic environment favoring the virulence of Candida species, and interactions between Candida-bacteria and host immunity.

CLINICAL SIGNIFICANCE

Mechanical plaque control is the most common treatment for periodontitis, but its effectiveness may be limited, particularly when dealing with systemic risk factors. Understanding the specific role of Candida in periodontitis illuminates innovative approaches for managing the ecological balance in periodontal health.

Photosensitizer-Amplified Antimicrobial Materials for Broad-Spectrum Ablation of Resistant Pathogens in Ocular Infections

The emergence of multidrug resistant (MDR) pathogens and the scarcity of new potent antibiotics and antifungals are one of the biggest threats to human health. Antimicrobial photodynamic therapy (aPDT) combines light and photosensitizers to kill drug-resistant pathogens; however, there are limited materials that can effectively ablate different classes of infective pathogens. In the present work, a new class of benzodiazole-paired materials is designed as highly potent PDT agents with broad-spectrum antimicrobial activity upon illumination with nontoxic light. The results mechanistically demonstrate that the energy transfer and electron transfer between nonphotosensitive and photosensitive benzodiazole moieties embedded within pathogen-binding peptide sequences result in increased singlet oxygen generation and enhanced phototoxicity. Chemical optimization renders PEP3 as a novel PDT agent with remarkable activity against MDR bacteria and fungi as well as pathogens at different stages of development (e.g., biofilms, spores, and fungal hyphae), which also prove effective in an ex vivo porcine model of microbial keratitis. The chemical modularity of this strategy and its general compatibility with peptide-based targeting agents will accelerate the design of highly photosensitive materials for antimicrobial PDT.

Phenotypic characterization of HAM1, a novel mating regulator of the fungal pathogen Cryptococcus neoformans

Cryptococcus neoformans is a fungal pathogen responsible for >200,000 yearly cases with a mortality as high as 81%. This burden results, in part, from an incomplete understanding of its pathogenesis and ineffective antifungal treatments; hence, there is a pressing need to understand the biology and host interactions of this yeast to develop improved treatments. Protein palmitoylation is important for cryptococcal virulence, and we previously identified the substrates of its main palmitoyl transferase. One of them was encoded by the uncharacterized gene CNAG_02129. In the filamentous fungus Neurospora crassa, a homolog of this gene named hyphal anastomosis protein 13 plays a role in proper cellular communication and filament fusion. In Cryptococcus, cellular communication is essential during mating; therefore, we hypothesized that CNAG_02129, which we named hyphal anastomosis protein 1 (HAM1), may play a role in mating. We found that ham1Δ mutants produce more fusion products during mating, filament more robustly, and exhibit competitive fitness defects under mating and non-mating conditions. Additionally, we found several differences with the major virulence factor, the polysaccharide capsule, that may affect virulence, consistent with prior studies linking virulence to mating. We observed that ham1Δ mutants have decreased capsule attachment and transfer but exhibit higher amounts of exopolysaccharide shedding and biofilm production. Finally, HAM1 expression is significantly lower in mating media relative to non-mating conditions, consistent with it acting as a negative regulator of mating. Understanding the connection between mating and virulence in C. neoformans may open new avenues of investigation into ways to improve the treatment of this disease.

IMPORTANCE

Fungal mating is a vital part of the lifecycle of the pathogenic yeast Cryptococcus neoformans. More than just ensuring the propagation of the species, mating allows for sexual reproduction to occur and generates genetic diversity as well as infectious propagules that can invade mammalian hosts. Despite its importance in the biology of this pathogen, we still do not know all of the major players regulating the mating process and if they are involved or impact its pathogenesis. Here, we identified a novel negative regulator of mating that also affects certain cellular characteristics known to be important for virulence. This gene, which we call HAM1, is widely conserved across the cryptococcal family as well as in many pathogenic fungal species. This study will open new avenues of exploration regarding the function of uncharacterized but conserved genes in a variety of pathogenic fungal species and specifically in serotype A of C. neoformans.

Sur7 mediates a novel pathway for PI4,5P2 regulation in C. albicans that promotes stress resistance and cell wall morphogenesis

The human fungal pathogen Candida albicans can cause lethal systemic infections due to its ability to resist stress from the host and to undergo invasive hyphal growth. Previous studies showed that plasma membrane MCC/eisosome domains were important for virulence by promoting the ability of Sur7 to mediate normal cell wall morphogenesis and stress resistance. The sur7Δ mutant displayed abnormal clusters of PI4,5P2, suggesting that misregulation of this lipid underlies the sur7Δ phenotype. To test this, we increased PI4,5P2 levels by deleting combinations of the three PI4,5P2 5' phosphatase genes (INP51, INP52, and INP54) and found that some combinations, such as inp51Δ inp52Δ, gave phenotypes similar the sur7Δ mutant. In contrast, deleting one copy of MSS4, the gene that encodes the 5' kinase needed to create PI4,5P2, reduced the abnormal PI4,5P2 clusters and also decreased the abnormal cell wall and stress sensitive phenotypes of the sur7Δ mutant. Additional studies support a model that the abnormal PI4,5P2 patches recruit septin proteins, which in turn promote aberrant cell wall growth. These results identify Sur7 as a novel regulator of PI4,5P2 and highlight the critical role of PI4,5P2 in the regulation of C. albicans virulence properties.

Genomic and morphological characterization of Knufia obscura isolated from the Mars 2020 spacecraft assembly facility

Members of the family Trichomeriaceae, belonging to the Chaetothyriales order and the Ascomycota phylum, are known for their capability to inhabit hostile environments characterized by extreme temperatures, oligotrophic conditions, drought, or presence of toxic compounds. The genus Knufia encompasses many polyextremophilic species. In this report, the genomic and morphological features of the strain FJI-L2-BK-P2 presented, which was isolated from the Mars 2020 mission spacecraft assembly facility located at the Jet Propulsion Laboratory in Pasadena, California. The identification is based on sequence alignment for marker genes, multi-locus sequence analysis, and whole genome sequence phylogeny. The morphological features were studied using a diverse range of microscopic techniques (bright field, phase contrast, differential interference contrast and scanning electron microscopy). The phylogenetic marker genes of the strain FJI-L2-BK-P2 exhibited highest similarities with type strain of Knufia obscura (CBS 148926T) that was isolated from the gas tank of a car in Italy. To validate the species identity, whole genomes of both strains (FJI-L2-BK-P2 and CBS 148926T) were sequenced, annotated, and strain FJI-L2-BK-P2 was confirmed as K. obscura. The morphological analysis and description of the genomic characteristics of K. obscura FJI-L2-BK-P2 may contribute to refining the taxonomy of Knufia species. Key morphological features are reported in this K. obscura strain, resembling microsclerotia and chlamydospore-like propagules. These features known to be characteristic features in black fungi which could potentially facilitate their adaptation to harsh environments.

Maxillary Mucormycotic Osteonecrosis as a Manifestation of Post-COVID-19 Infection in Non-diabetic Patients: Report of Two Cases

Mucormycosis is a rare, opportunistic fungal infection prevalent in the elderly, especially in patients with uncontrolled diabetes or a compromised immune system. However, the outbreak of the pandemic declared by the World Health Organization in late 2019 increased the incidence of mucormycosis cases in COVID-19 patients due to increased steroid usage that resulted in an immunocompromised state. The current report presents two cases of oral mucormycotic osteomyelitis in patients who developed diabetes post-COVID infection, along with a review and relevant literature.

Phenotypic characterization of HAM1, a novel mating regulator of the fungal pathogen Cryptococcus neoformans

Cryptococcus neoformans is a fungal pathogen responsible for >200,000 yearly cases with a mortality as high as 81%. This burden results, in part, from an incomplete understanding of its pathogenesis and ineffective antifungal treatments; hence, there is a pressing need to understand the biology and host interactions of this yeast to develop improved treatments. Protein palmitoylation is important for cryptococcal virulence, and we previously identified the substrates of its main palmitoyl transferase. One of them was encoded by the uncharacterized gene CNAG_02129. In the filamentous fungus Neurospora crassa, a homolog of this gene named HAM-13 plays a role in proper cellular communication and filament fusion. In Cryptococcus, cellular communication is essential during mating, therefore we hypothesized that CNAG_02129, which we named HAM1, may play a role in mating. We found that ham1Δ mutants produce more fusion products during mating, filament more robustly, and exhibit competitive fitness defects under mating and non-mating conditions. Additionally, we found several differences with the major virulence factor, the polysaccharide capsule, that may affect virulence, consistent with prior studies linking virulence to mating. We observed that ham1Δ mutants have decreased capsule attachment and transfer but exhibit higher amounts of exopolysaccharide shedding and biofilm production. Lastly, HAM1 expression is significantly lower in mating media relative to non-mating conditions, consistent with it acting as a negative regulator of mating. Understanding the connection between mating and virulence in C. neoformans may open new avenues of investigation into ways to improve the treatment of this disease.

Single-Molecule Fluorescent In Situ Hybridization (smFISH) for RNA Detection in the Fungal Pathogen Candida albicans

Candida albicans is the most prevalent human fungal pathogen. Its pathogenicity is linked to the ability of C. albicans to reversibly change morphology and to grow as yeast, pseudohyphae, or hyphal cells in response to environmental stimuli. Understanding the molecular regulation controlling those morphological switches remains a challenge that, if solved, could help eradicate C. albicans infections.While numerous studies investigated gene expression changes occurring during C. albicans morphological switches using bulk approaches (e.g., RNA sequencing), here we describe a single-cell and single-molecule RNA imaging and analysis protocol to measure absolute mRNA counts in morphologically intact cells. To detect endogenous mRNAs in single fixed cells, we optimized a single-molecule fluorescent in situ hybridization (smFISH) protocol for C. albicans, which allows one to quantify the differential expression of mRNAs in yeast, pseudohyphae, or hyphal cells. We quantified the expression of two mRNAs, a cell cycle-controlled mRNA (CLB2) and a transcription factor (EFG1), which show expression changes in the different morphological cell types and nutrient conditions. In this protocol, we described in detail the major steps of this approach: growth and fixation, hybridization, imaging, cell segmentation, and mRNA spot analysis. Raw data is provided with the protocol to favor reproducibility. This approach could benefit the molecular characterization of C. albicans and other filamentous fungi, pathogenic or nonpathogenic.

Pleiotropic functions of SscA on the asexual spore of the human pathogenic fungus Aspergillus fumigatus

Asexual spores, called conidia, are key reproductive fungal particles that enable survival in harsh environmental conditions or host systems. The conidia can infect humans, animals, and plants to cause various fungal diseases. Transcription factors, including VosA, WetA, and SscA, have key roles in conidia formation and long-term survival in Aspergillus nidulans. Herein, we report the pleiotropic functions of SscA in the conidia of the human pathogen A. fumigatus. The deletion of sscA increased conidia formation despite decreased fungal growth. Absence of sscA impaired long-term survival and reduced spore resistance to various stresses, including heat, UV, and oxidation. Transcriptomic analyses showed that SscA involved the mRNA expression of cell wall organisation-related genes. Importantly, the sscA deletion mutant conidia contained an increased amount of β-glucan and chitin compared to wild type conidia. In addition, conidial gliotoxin production was decreased in the sscA deletion strain. Overall, SscA has pleiotropic roles in conidia formation, maturation and dormancy and mycotoxin production in A. fumigatus.

Turnover and bypass of p21-activated kinase during Cdc42-dependent MAPK signaling in yeast

Mitogen-activated protein kinase (MAPK) pathways regulate multiple cellular behaviors, including the response to stress and cell differentiation, and are highly conserved across eukaryotes. MAPK pathways can be activated by the interaction between the small GTPase Cdc42p and the p21-activated kinase (Ste20p in yeast). By studying MAPK pathway regulation in yeast, we recently found that the active conformation of Cdc42p is regulated by turnover, which impacts the activity of the pathway that regulates filamentous growth (fMAPK). Here, we show that Ste20p is regulated in a similar manner and is turned over by the 26S proteasome. This turnover did not occur when Ste20p was bound to Cdc42p, which presumably stabilized the protein to sustain MAPK pathway signaling. Although Ste20p is a major component of the fMAPK pathway, genetic approaches here identified a Ste20p-independent branch of signaling. Ste20p-independent signaling partially required the fMAPK pathway scaffold and Cdc42p-interacting protein, Bem4p, while Ste20p-dependent signaling required the 14-3-3 proteins, Bmh1p and Bmh2p. Interestingly, Ste20p-independent signaling was inhibited by one of the GTPase-activating proteins for Cdc42p, Rga1p, which unexpectedly dampened basal but not active fMAPK pathway activity. These new regulatory features of the Rho GTPase and p21-activated kinase module may extend to related pathways in other systems.

The mRNA stability factor Khd4 defines a specific mRNA regulon for membrane trafficking in the pathogen Ustilago maydis

Fungal pathogens depend on sophisticated gene expression programs for successful infection. A crucial component is RNA regulation mediated by RNA-binding proteins (RBPs). However, little is known about the spatiotemporal RNA control mechanisms during fungal pathogenicity. Here, we discover that the RBP Khd4 defines a distinct mRNA regulon to orchestrate membrane trafficking during pathogenic development of Ustilago maydis. By establishing hyperTRIBE for fungal RBPs, we generated a comprehensive transcriptome-wide map of Khd4 interactions in vivo. We identify a defined set of target mRNAs enriched for regulatory proteins involved, e.g., in GTPase signaling. Khd4 controls the stability of target mRNAs via its cognate regulatory element AUACCC present in their 3' untranslated regions. Studying individual examples reveals a unique link between Khd4 and vacuole maturation. Thus, we uncover a distinct role for an RNA stability factor defining a specific mRNA regulon for membrane trafficking during pathogenicity.

Frequent transitions in mating-type locus chromosomal organization in Malassezia and early steps in sexual reproduction

Fungi in the basidiomycete genus Malassezia are the most prevalent eukaryotic microbes resident on the skin of human and other warm-blooded animals and have been implicated in skin diseases and systemic disorders. Analysis of Malassezia genomes revealed that key adaptations to the skin microenvironment have a direct genomic basis, and the identification of mating/meiotic genes suggests a capacity to reproduce sexually, even though no sexual cycle has yet been observed. In contrast to other bipolar or tetrapolar basidiomycetes that have either two linked mating-type-determining (MAT) loci or two MAT loci on separate chromosomes, in Malassezia species studied thus far the two MAT loci are arranged in a pseudobipolar configuration (linked on the same chromosome but capable of recombining). By generating additional chromosome-level genome assemblies, and an improved Malassezia phylogeny, we infer that the pseudobipolar arrangement was the ancestral state of this group and revealed six independent transitions to tetrapolarity, seemingly driven by centromere fission or translocations in centromere-flanking regions. Additionally, in an approach to uncover a sexual cycle, Malassezia furfur strains were engineered to express different MAT alleles in the same cell. The resulting strains produce hyphae reminiscent of early steps in sexual development and display upregulation of genes associated with sexual development as well as others encoding lipases and a protease potentially relevant for pathogenesis of the fungus. Our study reveals a previously unseen genomic relocation of mating-type loci in fungi and provides insight toward the identification of a sexual cycle in Malassezia, with possible implications for pathogenicity.

Frequent transitions in mating-type locus chromosomal organization in Malassezia and early steps in sexual reproduction

Fungi in the basidiomycete genus Malassezia are the most prevalent eukaryotic microbes resident on the skin of human and other warm-blooded animals and have been implicated in skin diseases and systemic disorders. Analysis of Malassezia genomes revealed that key adaptations to the skin microenvironment have a direct genomic basis, and the identification of mating/meiotic genes suggests a capacity to reproduce sexually, even though no sexual cycle has yet been observed. In contrast to other bipolar or tetrapolar basidiomycetes that have either two linked mating-type-determining ( MAT ) loci or two MAT loci on separate chromosomes, in Malassezia species studied thus far the two MAT loci are arranged in a pseudobipolar configuration (linked on the same chromosome but capable of recombining). By incorporating newly generated chromosome-level genome assemblies, and an improved Malassezia phylogeny, we infer that the pseudobipolar arrangement was the ancestral state of this group and revealed six independent transitions to tetrapolarity, seemingly driven by centromere fission or translocations in centromere- flanking regions. Additionally, in an approach to uncover a sexual cycle, Malassezia furfur strains were engineered to express different MAT alleles in the same cell. The resulting strains produce hyphae reminiscent of early steps in sexual development and display upregulation of genes associated with sexual development as well as others encoding lipases and a protease potentially relevant for pathogenesis of the fungus. Our study reveals a previously unseen genomic relocation of mating-type loci in fungi and provides insight towards the discovery of a sexual cycle in Malassezia , with possible implications for pathogenicity.

Significance Statement

Malassezia , the dominant fungal group of the mammalian skin microbiome, is associated with numerous skin disorders. Sexual development and yeast-to-hyphae transitions, governed by genes at two mating-type ( MAT ) loci, are thought to be important for fungal pathogenicity. However, Malassezia sexual reproduction has never been observed. Here, we used chromosome-level assemblies and comparative genomics to uncover unforeseen transitions in MAT loci organization within Malassezia , possibly related with fragility of centromeric-associated regions. Additionally, by expressing different MAT alleles in the same cell, we show that Malassezia can undergo hyphal development and this phenotype is associated with increased expression of key mating genes along with other genes known to be virulence factors, providing a possible connection between hyphal development, sexual reproduction, and pathogenicity.

World Health Organization's first-ever release of a fungal priority pathogens list: A reply action proposal for the prevention and treatment of fungal pathogens

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A facile and scalable strategy for constructing Janus cotton fabric with persistent antibacterial activity

Natural cotton fibers have attached considerable attention due to their excellent wearing comfort, breathability and warmth. However, it remains a challenge to devise a scalable and facile strategy to retrofit natural cotton fibers. Here, the cotton fiber surface was oxidized by sodium periodate with a mist process, then [2-(methacryloyloxy) ethyl] trimethylammonium chloride (DMC) was co-polymerized with hydroxyethyl acrylate (HA) to obtain an antibacterial cationic polymer (DMC-co-HA). The self-synthesized polymer was covalently grafted onto the aldehyde-functionalized cotton fibers via an acetal reaction between hydroxyl groups of the polymer and aldehyde groups of the oxidized cotton surface. Finally, the resulted Janus functionalized cotton fabric (JanCF) revealed robust and persistent antimicrobial activity. The antibacterial test showed that when the molar ratio of DMC/HA was 50: 1, JanCF possessed the best BR (bacterial reduction) values of 100 % against Escherichia coli and Staphylococcus aureus. Furthermore, the BR values could be maintained over 95 % even after the durability test. In addition, JanCF exhibited excellent antifungal activity against Candida albicans. The cytotoxicity assessment confirmed that JanCF exhibited a reliable safety effect on human skin. Particularly, the intrinsic outstanding characteristics (strength, flexibility, etc.) of the cotton fabric were not considerably deteriorated compared to the control samples.

New Features Surrounding the Cdc42-Ste20 Module that Regulates MAP Kinase Signaling in Yeast

Mitogen-activated protein kinase (MAPK) pathways regulate multiple cellular responses, including the response to stress and cell differentiation, and are highly conserved across eukaryotes from yeast to humans. In yeast, the canonical activation of several MAPK pathways includes the interaction of the small GTPase Cdc42p with the p21-activated kinase (PAK) Ste20p. We recently found that the active conformation of Cdc42p is regulated by turnover, which impacts the activity of the pathway that regulates filamentous growth (fMAPK). Here, we show that Ste20p is turned over by the 26S proteasome. Ste20p was stabilized when bound to Cdc42p, presumably to sustain MAPK pathway signaling. Ste20p is a major conduit by which signals flow through the fMAPK pathway; however, by genetic approaches we also identified a Ste20p-independent branch of the fMAPK pathway. Ste20p-dependent signaling required the 14-3-3 proteins, Bmh1p and Bmh2p, while Ste20p-independent signaling required the fMAPK pathway adaptor and Cdc42p-interacting protein, Bem4p. Ste20p-independent signaling was inhibited by one of the GTPase-activating proteins for Cdc42p in the fMAPK pathway, Rga1p, which also dampened basal but not active fMAPK pathway activity. Finally, the polarity adaptor and Cdc42p-interacting protein, Bem1p, which also regulates the fMAPK pathway, interacts with the tetra-span protein Sho1p, connecting a sensor at the plasma membrane to a protein that regulates the GTPase module. Collectively, these data reveal new regulatory features surrounding a Rho-PAK module that may extend to other pathways that control cell differentiation.

Plasma Gelsolin Enhances Phagocytosis of Candida auris by Human Neutrophils through Scavenger Receptor Class B

In addition to its role as an actin-depolymerizing factor in the blood, plasma gelsolin (pGSN) binds bacterial molecules and stimulates the phagocytosis of bacteria by macrophages. Here, using an in vitro system, we assessed whether pGSN could also stimulate phagocytosis of the fungal pathogen Candida auris by human neutrophils. The extraordinary ability of C. auris to evade immune responses makes it particularly challenging to eradicate in immunocompromised patients. We demonstrate that pGSN significantly enhances C. auris uptake and intracellular killing. Stimulation of phagocytosis was accompanied by decreased neutrophil extracellular trap (NET) formation and reduced secretion of proinflammatory cytokines. Gene expression studies revealed pGSN-dependent upregulation of scavenger receptor class B (SR-B). Inhibition of SR-B using sulfosuccinimidyl oleate (SSO) and block lipid transport-1 (BLT-1) decreased the ability of pGSN to enhance phagocytosis, indicating that pGSN potentiates the immune response through an SR-B-dependent pathway. These results suggest that the response of the host's immune system during C. auris infection may be enhanced by the administration of recombinant pGSN. IMPORTANCE The incidence of life-threatening multidrug-resistant Candida auris infections is rapidly growing, causing substantial economic costs due to outbreaks in hospital wards. Primary and secondary immunodeficiencies in susceptible individuals, such as those with leukemia, solid organ transplants, diabetes, and ongoing chemotherapy, often correlate with decreased plasma gelsolin concentration (hypogelsolinemia) and impairment of innate immune responses due to severe leukopenia. Immunocompromised patients are predisposed to superficial and invasive fungal infections. Morbidity caused by C. auris among immunocompromised patients can be as great as 60%. In the era of ever-growing fungal resistance in an aging society, it is critical to seek novel immunotherapies that may help combat these infections. The results reported here suggest the possibility of using pGSN as an immunomodulator of the immune response by neutrophils during C. auris infection.

Fungal Virus, FgHV1-Encoded p20 Suppresses RNA Silencing through Single-Strand Small RNA Binding

Fungal viruses are widespread in fungi infecting plants, insects and animals. High-throughput sequencing has rapidly led to the discovery of fungal viruses. However, the interactive exploration between fungi and viruses is relatively limited. RNA silencing is the fundamental antivirus pathway in fungi. Fusarium graminearum small RNA (sRNA) pattern was regulated by Fusarium graminearum hypovirus 1 (FgHV1) infection, indicating the activation of RNA silencing in virus defense. In this study, we focused on the function of an uncharacterized protein sized at 20 kD (p20) encoded by FgHV1. In the agro-infiltration assay, p20 was identified as a novel fungal RNA silencing suppressor. p20 can block systemic RNA silencing signals besides local RNA silencing suppression. We further elucidated the RNA silencing suppression mechanism of p20. The single-strand sRNA, instead of double-strand sRNA, can be incorporated by p20 in electrophoretic mobility shift assay. p20 binds sRNA originating from virus and non-virus sources in a non-sequence-specific manner. In addition, The F. graminearum 22 and 23-nt sRNA abundance and pathways related to RNA processing and redox regulation were regulated by p20. Our study revealed the first fungal virus-encoded RNA silencing suppressor with sRNA binding capability.

Synthetic physical contact-remodeled rhizosphere microbiome for enhanced phytoremediation

Phytoremediation is a prevalent strategy to treat environmental pollution caused by heavy metals and eutrophication-related pollutants. Although rhizosphere microbiome is critical for phytoremediation, it remains a great challenge to artificially remodel rhizosphere microbiome for enhancing multiple pollutant treatment. In this study, we designed a synthetic bacterium to strengthen physical contact between natural microbes and plant roots for remodeling the Eichhornia crassipes rhizosphere microbiome during phytoremediation. The synthetic bacterium EcCMC was constructed by introducing a surface-displayed synthetic protein CMC composed of two glucan-binding domains separated by the sequence of the fluorescent protein mCherry. This synthetic bacterium strongly bound glucans and recruited natural glucan-producing bacterial and fungal cells. Microbiome and metabolomic analysis revealed that EcCMC remarkably remodeled rhizosphere microbiome and increased stress response-related metabolites, leading to the increased activity of antioxidant enzymes involved in stress resistance. The remodeled microbiome further promoted plant growth, and enhanced accumulation of multiple pollutants into the plants, with the removal efficiency of the heavy metal cadmium, total organic matters, total nitrogen, total potassium, and total phosphorus reaching up to 98%, 80%, 97%, 93%, and 90%, respectively. This study sheds a novel light on remodeling of rhizosphere microbiome for enhanced phytoremediation of water and soil systems.

Innate immune responses against the fungal pathogen Candida auris

Candida auris is a multidrug-resistant human fungal pathogen responsible for nosocomial outbreaks worldwide. Although considerable progress has increased our understanding of the biological and clinical aspects of C. auris, its interaction with the host immune system is only now beginning to be investigated in-depth. Here, we compare the innate immune responses induced by C. auris BJCA001 and Candida albicans SC5314 in vitro and in vivo. Our results indicate that C. auris BJCA001 appears to be less immunoinflammatory than C. albicans SC5314, and this differential response correlates with structural features of the cell wall.

Candida auris is a multidrug-resistant human fungal pathogen responsible for nosocomial outbreaks worldwide. Here, the authors identify differential innate immune responses induced by C. auris and Candida albicans in vitro and in vivo, which correlate with structural features of the cell wall.

Plasma Membrane Phosphatidylinositol 4-Phosphate Is Necessary for Virulence of Candida albicans

Phosphatidylinositol lipids regulate key processes, including vesicle trafficking and cell polarity. A recent study identified novel roles for phosphatidylinositol 4-phosphate (PI₄P) in the plasma membrane of the fungal pathogen Candida albicans, including polarized hyphal growth and cell wall organization. Studies in other organisms were not able to separate the roles of PI₄P in the plasma membrane and Golgi, but the C. albicans plasma membrane pool of PI₄P could be selectively eliminated by deleting the STT4 kinase, which creates PI₄P. Interestingly, stt4Δ mutants were strongly defective in disseminated candidiasis in mice but were not defective in an oral infection. This suggested that abnormal exposure of β-glucan in the mutant cell walls increased recruitment of innate immune cells during disseminated infection, which is not expected to impact oral infection. These results highlight novel roles of PI₄P and reinforce the need to test the virulence of C. albicans mutants at different host sites.

The sat1 Gene Is Required for the Growth and Virulence of the Human Pathogenic Fungus Aspergillus fumigatus

Aspergillus fumigatus is an important opportunistic pathogenic fungus that causes invasive aspergillosis in immunocompromised humans. Regulated fungal growth is essential for disease development and progression. Thus, screening for genes that regulate fungal growth may lead to the identification of potential therapeutic targets for invasive aspergillosis (IA). Screening of the transfer DNA (T-DNA) random-insertion A. fumigatus mutants identified a severe growth deficiency mutant AFM2954 and featured sat1 as the mutated gene described as a putative intracellular protein transporter of unknown function. The deletion of sat1 exhibited severe growth defects and significantly increased the nematode and mouse survival rates and decreased the fungal loads and histopathological damages in mouse lungs. Transcriptomic analyses revealed expression changes associated with the cell wall synthesis, the tricarboxylic acid cycle (TCA cycle), and oxidative phosphorylation genes in the sat1 mutant. Deletion of the gene resulted in resistance to cell wall-perturbing agents and thickened cell wall as well as reduced ATP contents and mitochondrial membrane potential, suggested that sat1 affected the cell wall synthesis and mitochondrial function of A. fumigatus. All together, our study uncovered novel functions of sat1 in growth and virulence of A. fumigatus and provided a theoretical basis for the development of new therapeutic target for treating IA patients. IMPORTANCE Aspergillus fumigatus is the main causative agent of invasive aspergillosis in immunocompromised hosts, with up to 90% lethality. Nevertheless, the fungal factors that regulate the pathogenesis of A. fumigatus remain largely unknown. Better understanding of the mechanisms controlling growth of A. fumigatus may provide novel therapeutic targets. In the present study, we characterized sat1 in the opportunistic pathogen A. fumigatus. The function of sat1 remains unknown. We proved its important role in growth and virulence, likely because of its effects on cell wall synthesis and mitochondrial functions.

Galectins as potential therapeutic targets in STIs in the female genital tract

Every day, more than one million people worldwide acquire a sexually transmitted infection (STI). This public health problem has a direct effect on women's reproductive and sexual health as STIs can cause irreversible damage to fertility and can have negative consequences associated with discrimination and social exclusion. Infection with one sexually transmitted pathogen predisposes to co-infection with others, suggesting the existence of shared pathways that serve as molecular links between these diseases. Galectins, a family of β-galactoside-binding proteins, have emerged as endogenous mediators that facilitate cell-surface binding, internalization and cell invasion of many sexually transmitted pathogens, including Chlamydia trachomatis, Neisseria gonorrhoeae, Trichomonas vaginalis, Candida albicans, HIV and herpes simplex virus. The ability of certain galectins to dimerize or form multimeric complexes confers the capacity to interact simultaneously with glycosylated ligands on both the pathogen and the cervico-vaginal tissue on these proteins. Galectins can act as a bridge by engaging glycans from the pathogen surface and glycosylated receptors from host cells, which is a mechanism that has been shown to be shared by several sexually transmitted pathogens. In the case of viruses and obligate intracellular bacteria, binding to the cell surface promotes pathogen internalization and cell invasion. Inflammatory responses that occur in cervico-vaginal tissue might trigger secretion of galectins, which in turn control the establishment, evolution and severity of STIs. Thus, galectin-targeted therapies could potentially prevent or decrease STIs caused by a diverse array of pathogenic microorganisms; furthermore, anti-galectin agents might reduce treatment costs of STIs and reach the most vulnerable populations.

Controlling the Interaction between Fluorescent Gold Nanoclusters and Biointerfaces for Rapid Discrimination of Fungal Pathogens

Nondestructive detection and discrimination of fungal pathogens is essential for rapid and precise treatment, which further effectively prevents antifungal resistance from overused drugs. In this work, fluorescent gold nanoclusters served as the basis for discriminating Candida species. Varied on surface ligands, these gold nanoclusters demonstrated different optical properties as a result of the perturbation effects of ligands. The biointerface interaction between the surface ligands of gold nanoclusters and the cell walls of Candida species can be constructed, and their restriction on ligands perturbation effect produced enhanced fluorescence signals. Owing to the variation of the cell wall composition, cells of different Candida species demonstrated different degrees of association with the gold nanoclusters, leading to discriminable amounts of fluorescence enhancements. The reverse signal response from these gold nanoclusters gives rise to a synergistic and effective assay that allows identification of Candida species.

Mucormycosis Amid COVID-19 Crisis: Pathogenesis, Diagnosis, and Novel Treatment Strategies to Combat the Spread

The havoc unleashed by COVID-19 pandemic has paved way for secondary ominous fungal infections like Mucormycosis. It is caused by a class of opportunistic pathogens from the order Mucorales. Fatality rates due to this contagious infection are extremely high. Numerous clinical manifestations result in damage to multiple organs subject to the patient's underlying condition. Lack of a proper detection method and reliable treatment has made the management of this infection troublesome. Several reports studying the behavior pattern of Mucorales inside the host by modulation of its defense mechanisms have helped in understanding the pathogenesis of this angio-invasive infection. Many recent advances in diagnosis and treatment of this fungal infection have not been much beneficial. Therefore, there is a need to foster more viable strategies. This article summarizes current and imminent approaches that could aid effective management of these secondary infections in these times of global pandemic. It is foreseen that the development of newer antifungal drugs, antimicrobial peptides, and nanotechnology-based approaches for drug delivery would help combat this infection and curb its spread.

Integrative multi-omics profiling reveals cAMP-independent mechanisms regulating hyphal morphogenesis in Candida albicans

Microbial pathogens grow in a wide range of different morphologies that provide distinct advantages for virulence. In the fungal pathogen Candida albicans, adenylyl cyclase (Cyr1) is thought to be a master regulator of the switch to invasive hyphal morphogenesis and biofilm formation. However, faster growing cyr1Δ/Δ pseudorevertant (PR) mutants were identified that form hyphae in the absence of cAMP. Isolation of additional PR mutants revealed that their improved growth was due to loss of one copy of BCY1, the negative regulatory subunit of protein kinase A (PKA) from the left arm of chromosome 2. Furthermore, hyphal morphogenesis was improved in some of PR mutants by multigenic haploinsufficiency resulting from loss of large regions of the left arm of chromosome 2, including global transcriptional regulators. Interestingly, hyphal-associated genes were also induced in a manner that was independent of cAMP. This indicates that basal protein kinase A activity is an important prerequisite to induce hyphae, but activation of adenylyl cyclase is not needed. Instead, phosphoproteomic analysis indicated that the Cdc28 cyclin-dependent kinase and the casein kinase 1 family member Yck2 play key roles in promoting polarized growth. In addition, integrating transcriptomic and proteomic data reveals hyphal stimuli induce increased production of key transcription factors that contribute to polarized morphogenesis.

Occupational Histoplasmosis: Epidemiology and Prevention Measures

In areas where Histoplasma is endemic in the environment, occupations involving activities exposing workers to soil that contains bird or bat droppings may pose a risk for histoplasmosis. Occupational exposures are frequently implicated in histoplasmosis outbreaks. In this paper, we review the literature on occupationally acquired histoplasmosis. We describe the epidemiology, occupational risk factors, and prevention measures according to the hierarchy of controls.

Plasma Membrane Phosphatidylinositol-4-Phosphate Is Not Necessary for Candida albicans Viability yet Is Key for Cell Wall Integrity and Systemic Infection

Phosphatidylinositol phosphates are key phospholipids with a range of regulatory roles, including membrane trafficking and cell polarity. Phosphatidylinositol-4-phosphate [PI(4)P] at the Golgi apparatus is required for the budding-to-filamentous-growth transition in the human-pathogenic fungus Candida albicans; however, the role of plasma membrane PI(4)P is unclear. We have investigated the importance of this phospholipid in C. albicans growth, stress response, and virulence by generating mutant strains with decreased levels of plasma membrane PI(4)P, via deletion of components of the PI-4-kinase complex, i.e., Efr3, Ypp1, and Stt4. The amounts of plasma membrane PI(4)P in the efr3Δ/Δ and ypp1Δ/Δ mutants were ∼60% and ∼40%, respectively, of that in the wild-type strain, whereas it was nearly undetectable in the stt4Δ/Δ mutant. All three mutants had reduced plas7ma membrane phosphatidylserine (PS). Although these mutants had normal yeast-phase growth, they were defective in filamentous growth, exhibited defects in cell wall integrity, and had an increased exposure of cell wall β(1,3)-glucan, yet they induced a range of hyphal-specific genes. In a mouse model of hematogenously disseminated candidiasis, fungal plasma membrane PI(4)P levels directly correlated with virulence; the efr3Δ/Δ mutant had wild-type virulence, the ypp1Δ/Δ mutant had attenuated virulence, and the stt4Δ/Δ mutant caused no lethality. In the mouse model of oropharyngeal candidiasis, only the ypp1Δ/Δ mutant had reduced virulence, indicating that plasma membrane PI(4)P is less important for proliferation in the oropharynx. Collectively, these results demonstrate that plasma membrane PI(4)P levels play a central role in filamentation, cell wall integrity, and virulence in C. albicans. IMPORTANCE While the PI-4-kinases Pik1 and Stt4 both produce PI(4)P, the former generates PI(4)P at the Golgi apparatus and the latter at the plasma membrane, and these two pools are functionally distinct. To address the importance of plasma membrane PI(4)P in Candida albicans, we generated deletion mutants of the three putative plasma membrane PI-4-kinase complex components and quantified the levels of plasma membrane PI(4)P in each of these strains. Our work reveals that this phosphatidylinositol phosphate is specifically critical for the yeast-to-hyphal transition, cell wall integrity, and virulence in a mouse systemic infection model. The significance of this work is in identifying a plasma membrane phospholipid that has an infection-specific role, which is attributed to the loss of plasma membrane PI(4)P resulting in β(1,3)-glucan unmasking.

Malassezia spp. Yeasts of Emerging Concern in Fungemia

Malassezia spp. are lipid-dependent yeasts, inhabiting the skin and mucosa of humans and animals. They are involved in a variety of skin disorders in humans and animals and may cause bloodstream infections in severely immunocompromised patients. Despite a tremendous increase in scientific knowledge of these yeasts during the last two decades, the epidemiology of Malassezia spp. related to fungemia remains largely underestimated most likely due to the difficulty in the isolation of these yeasts species due to their lipid-dependence. This review summarizes and discusses the most recent literature on Malassezia spp. infection and fungemia, its occurrence, pathogenicity mechanisms, diagnostic methods, in vitro susceptibility testing and therapeutic approaches.