Extracellular vesicles of human pathogenic fungi

From High Protection to Lethal Effect: Diverse Outcomes of Immunization Against Invasive Candidiasis with Different Candida albicans Extracellular Vesicles

Extracellular vesicles (EVs) from Candida albicans can elicit immune responses, positioning them as promising acellular vaccine candidates. We characterized EVs from an avirulent C. albicans cell wall mutant (ecm33Δ) and evaluated their protective potential against invasive candidiasis. EVs from the yeast (YEVs) and hyphal (HEVs) forms of the SC5314 wild-type strain were also tested, yielding high survival rates with SC5314 YEV (91%) and ecm33 YEV immunization (64%). Surprisingly, HEV immunization showed a dual effect, resulting in 36% protection but also causing premature death in some mice. Proteomic analyses revealed distinct profiles among the top 100 proteins in the different EVs, which may explain these effects: a shared core of 50 immunogenic proteins such as Pgk1, Cdc19, and Fba1; unique, relevant immunogenic proteins in SC5314 YEVs; and proteins linked to pathogenesis, like Ece1 in SC5314 HEVs. Sera from SC5314 YEV-immunized mice showed the highest IgG2a titers and moderate IL-17, IFN-γ, and TNF-α levels, indicating the importance of both humoral and cellular responses for protection. These findings highlight the distinct immunogenic properties of C. albicans EVs, suggesting their potential in acellular vaccine development while emphasizing the need to carefully evaluate pathogenic risks associated with certain EVs.

Interkingdom Communication via Extracellular Vesicles: Unraveling Plant and Pathogen Interactions and Its Potential for Next-Generation Crop Protection

Recent advancements in the field of plant-pathogen interactions have spotlighted the role of extracellular vesicles (EVs) as pivotal mediators of cross-kingdom communication, offering new vistas for enhancing crop protection strategies. EVs are instrumental in the transport of small regulatory RNAs (sRNAs) and other bioactive molecules across species boundaries, thus playing a critical role in the molecular warfare between plants and pathogens. This review elucidates the sophisticated mechanisms by which plants utilize EVs to dispatch sRNAs that silence pathogenic genes, fortifying defenses against microbial threats. Highlighting both eukaryotic and prokaryotic systems, this review delves into the biogenesis, isolation, and functional roles of EVs, illustrating their importance not only in fundamental biological processes but also in potential therapeutic applications. Recent studies have illuminated the significant role of EVs in facilitating communication between plants and pathogens, highlighting their potential in host-defense mechanisms. However, despite these advancements, challenges remain in the efficient isolation and characterization of plant-derived EVs. Overcoming these challenges is critical for fully harnessing their potential in developing next-generation crop protection strategies. This review proposes innovative strategies for utilizing RNA-based interventions delivered via EVs to bolster plant resilience against diseases. By integrating the latest scientific findings with practical applications in agriculture, this review aims to enhance the connection between fundamental plant biology and the development of innovative crop management technologies.

Overview of extracellular vesicles in pathogens with special focus on human extracellular protozoan parasites

Extracellular vesicles (EVs) are lipid-bilayered membrane-delimited particles secreted by almost any cell type, involved in different functions according to the cell of origin and its state. From these, cell to cell communication, pathogen-host interactions and modulation of the immune response have been widely studied. Moreover, these vesicles could be employed for diagnostic and therapeutic purposes, including infections produced by pathogens of diverse types; regarding parasites, the secretion, characterisation, and roles of EVs have been studied in particular cases. Moreover, the heterogeneity of EVs presents challenges at every stage of studies, which motivates research in this area. In this review, we summarise some aspects related to the secretion and roles of EVs from several groups of pathogens, with special focus on the most recent research regarding EVs secreted by extracellular protozoan parasites.

Prokaryotic microvesicles Ortholog of eukaryotic extracellular vesicles in biomedical fields

Every single cell can communicate with other cells in a paracrine manner via the production of nano-sized extracellular vesicles. This phenomenon is conserved between prokaryotic and eukaryotic cells. In eukaryotic cells, exosomes (Exos) are the main inter-cellular bioshuttles with the potential to carry different signaling molecules. Likewise, bacteria can produce and release Exo-like particles, namely microvesicles (MVs) into the extracellular matrix. Bacterial MVs function with diverse biological properties and are at the center of attention due to their inherent therapeutic properties. Here, in this review article, the comparable biological properties between the eukaryotic Exos and bacterial MVs were highlighted in terms of biomedical application. Video Abstract.

Plant mRNAs move into a fungal pathogen via extracellular vesicles to reduce infection

Cross-kingdom small RNA trafficking between hosts and microbes modulates gene expression in the interacting partners during infection. However, whether other RNAs are also transferred is unclear. Here, we discover that host plant Arabidopsis thaliana delivers mRNAs via extracellular vesicles (EVs) into the fungal pathogen Botrytis cinerea. A fluorescent RNA aptamer reporter Broccoli system reveals host mRNAs in EVs and recipient fungal cells. Using translating ribosome affinity purification profiling and polysome analysis, we observe that delivered host mRNAs are translated in fungal cells. Ectopic expression of two transferred host mRNAs in B. cinerea shows that their proteins are detrimental to infection. Arabidopsis knockout mutants of the genes corresponding to these transferred mRNAs are more susceptible. Thus, plants have a strategy to reduce infection by transporting mRNAs into fungal cells. mRNAs transferred from plants to pathogenic fungi are translated to compromise infection, providing knowledge that helps combat crop diseases.

Yeast strains isolated from fermented beverage produce extracellular vesicles with anti-inflammatory effects

Extracellular vesicles (EVs) are lipid-bilayered particles, containing various biomolecules, including nucleic acids, lipids, and proteins, released by cells from all the domains of life and performing multiple communication functions. Evidence suggests that the interaction between host immune cells and fungal EVs induces modulation of the immune system. Most of the studies on fungal EVs have been conducted in the context of fungal infections; therefore, there is a knowledge gap in what concerns the production of EVs by yeasts in other contexts rather than infection and that may affect human health. In this work, we characterized EVs obtained by Saccharomyces cerevisiae and Pichia fermentans strains isolated from a fermented milk product with probiotic properties. The immunomodulation abilities of EVs produced by these strains have been studied in vitro through immune assays after internalization from human monocyte-derived dendritic cells. Results showed a significant reduction in antigen presentation activity of dendritic cells treated with the fermented milk EVs. The small RNA fraction of EVs contained mainly yeast mRNA sequences, with a few molecular functions enriched in strains of two different species isolated from the fermented milk. Our results suggest that one of the mechanisms behind the anti-inflammatory properties of probiotic foods could be mediated by the interactions of human immune cells with yeast EVs.

Extracellular vesicles in bacterial and fungal diseases - Pathogenesis to diagnostic biomarkers

Intercellular communication among microbes plays an important role in disease exacerbation. Recent advances have described small vesicles, termed as "extracellular vesicles" (EVs), previously disregarded as "cellular dust" to be vital in the intracellular and intercellular communication in host-microbe interactions. These signals have been known to initiate host damage and transfer of a variety of cargo including proteins, lipid particles, DNA, mRNA, and miRNAs. Microbial EVs, referred to generally as "membrane vesicles" (MVs), play a key role in disease exacerbation suggesting their importance in pathogenicity. Host EVs help coordinate antimicrobial responses and prime the immune cells for pathogen attack. Hence EVs with their central role in microbe-host communication, may serve as important diagnostic biomarkers of microbial pathogenesis. In this review, we summarize current research regarding the roles of EVs as markers of microbial pathogenesis with specific focus on their interaction with host immune defence and their potential as diagnostic biomarkers in disease conditions.

Extracellular Vesicles and Bacteriophages: New Directions in Environmental Biocolloid Research

There is a long-standing appreciation among environmental engineers and scientists regarding the importance of biologically derived colloidal particles and their environmental fate. This interest has been recently renewed in considering bacteriophages and extracellular vesicles, which are each poised to offer engineers unique insights into fundamental aspects of environmental microbiology and novel approaches for engineering applications, including advances in wastewater treatment and sustainable agricultural practices. Challenges persist due to our limited understanding of interactions between these nanoscale particles with unique surface properties and their local environments. This review considers these biological particles through the lens of colloid science with attention given to their environmental impact and surface properties. We discuss methods developed for the study of inert (nonbiological) particle-particle interactions and the potential to use these to advance our understanding of the environmental fate and transport of extracellular vesicles and bacteriophages.

Immunomodulatory Potential of Fungal Extracellular Vesicles: Insights for Therapeutic Applications

Extracellular vesicles (EVs) are membranous vesicular organelles that perform a variety of biological functions including cell communication across different biological kingdoms. EVs of mammals and, to a lesser extent, bacteria have been deeply studied over the years, whereas investigations of fungal EVs are still in their infancy. Fungi, encompassing both yeast and filamentous forms, are increasingly recognized for their production of extracellular vesicles (EVs) containing a wealth of proteins, lipids, and nucleic acids. These EVs play pivotal roles in orchestrating fungal communities, bolstering pathogenicity, and mediating interactions with the environment. Fungal EVs have emerged as promising candidates for innovative applications, not only in the management of mycoses but also as carriers for therapeutic molecules. Yet, numerous questions persist regarding fungal EVs, including their mechanisms of generation, release, cargo regulation, and discharge. This comprehensive review delves into the present state of knowledge regarding fungal EVs and provides fresh insights into the most recent hypotheses on the mechanisms driving their immunomodulatory properties. Furthermore, we explore the considerable potential of fungal EVs in the realms of medicine and biotechnology. In the foreseeable future, engineered fungal cells may serve as vehicles for tailoring cargo- and antigen-specific EVs, positioning them as invaluable biotechnological tools for diverse medical applications, such as vaccines and drug delivery.

Extracellular RNAs released by plant-associated fungi: from fundamental mechanisms to biotechnological applications

Extracellular RNAs are an emerging research topic in fungal-plant interactions. Fungal plant pathogens and symbionts release small RNAs that enter host cells to manipulate plant physiology and immunity. This communication via extracellular RNAs between fungi and plants is bidirectional. On the one hand, plants release RNAs encapsulated inside extracellular vesicles as a defense response as well as for intercellular and inter-organismal communication. On the other hand, recent reports suggest that also full-length mRNAs are transported within fungal EVs into plants, and these fungal mRNAs might get translated inside host cells. In this review article, we summarize the current views and fundamental concepts of extracellular RNAs released by plant-associated fungi, and we discuss new strategies to apply extracellular RNAs in crop protection against fungal pathogens. KEY POINTS: • Extracellular RNAs are an emerging topic in plant-fungal communication. • Fungi utilize RNAs to manipulate host plants for colonization. • Extracellular RNAs can be engineered to protect plants against fungal pathogens.

Characteristics and potential clinical applications of the extracellular vesicles of human pathogenic Fungi

Extracellular vesicles (EVs) are a heterogeneous group of lipid membrane-enclosed compartments that contain different biomolecules and are released by almost all living cells, including fungal genera. Fungal EVs contain multiple bioactive components that perform various biological functions, such as stimulation of the host immune system, transport of virulence factors, induction of biofilm formation, and mediation of host-pathogen interactions. In this review, we summarize the current knowledge on EVs of human pathogenic fungi, mainly focusing on their biogenesis, composition, and biological effects. We also discuss the potential markers and therapeutic applications of fungal EVs.

Exploring Extracellular Vesicles of Probiotic Yeast as Carriers of Biologically Active Molecules Transferred to Human Intestinal Cells

Extracellular vesicles (EVs) are nanoparticles containing various bioactive cargos-e.g., proteins, RNAs, and lipids-that are released into the environment by all cell types. They are involved in, amongst other functions, intercellular communication. This article presents studies on EVs produced by the probiotic yeast Saccharomyces boulardii CNCM I-745. The size distribution and concentration of EVs in the liquid culture of yeast were estimated. Moreover, the vesicles of S. boulardii were tested for their cytotoxicity against three model human intestinal cell lines. This study did not show any significant negative effect of yeast EVs on these cells under tested conditions. In addition, EVs of S. boulardii were verified for their ability to internalize in vitro with human cells and transfer their cargo. The yeast vesicles were loaded with doxorubicin, an anticancer agent, and added to the cellular cultures. Subsequently, microscopic observations revealed that these EVs transferred the compound to human intestinal cell lines. A cytotoxicity test confirmed the activity of the transferred doxorubicin. Detailed information about the proteins present in EVs might be important in terms of exploring yeast EVs as carriers of active molecules. Thus, proteomic analysis of the EV content was also conducted within the present study, and it allowed the identification of 541 proteins after matching them to the Saccharomyces Genome Database (SGD). Altogether, this study provides strong evidence that the EVs of the probiotic CNCM I-745 strain could be considered a drug delivery system.

Extracellular vesicles derived from Talaromyces marneffei contain immunogenic compounds and modulate THP-1 macrophage responses

Pathogenic eukaryotes including fungi release extracellular vesicles (EVs) which are composed of a variety of bioactive components, including peptides, nucleic acids, polysaccharides, and membrane lipids. EVs contain virulence-associated molecules suggesting a crucial role of these structures in disease pathogenesis. EVs derived from the pathogenic yeast phase of Talaromyces (Penicillium) marneffei, a causative agent of systemic opportunistic mycoses "talaromycosis," were studied for their immunogenic components and immunomodulatory properties. Some important virulence factors in EVs including fungal melanin and yeast phase specific mannoprotein were determined by immunoblotting. Furthermore, fluorescence microscopy revealed that T. marneffei EVs were internalized by THP-1 human macrophages. Co-incubation of T. marneffei EVs with THP-1 human macrophages resulted in increased levels of supernatant interleukin (IL)-1β, IL-6 and IL-10. The expression of THP-1 macrophage surface CD86 was significantly increased after exposed to T. marneffei EVs. These findings support the hypothesis that fungal EVs play an important role in macrophage "classical" M1 polarization. T. marneffei EVs preparations also increased phagocytosis, suggesting that EV components stimulate THP-1 macrophages to produce effective antimicrobial compounds. In addition, T. marneffei EVs stimulated THP-1 macrophages were more effective at killing T. marneffei conidia. These results indicate that T. marneffei EVs can potently modulate macrophage functions, resulting in the activation of these innate immune cells to enhance their antimicrobial activity.

Extracellular Vesicles from Candida haemulonii var. vulnera Modulate Macrophage Oxidative Burst

Members of the Candida haemulonii species complex are multidrug-resistant emergent yeast pathogens able to cause superficial and invasive infections in risk populations. Fungal extracellular vesicles (EVs) play a critical role in the pathogenicity and virulence of several species and may perform essential functions during infections, such as carrying virulence factors that behave in two-way communications with the host, affecting survival and fungal resistance. Our study aimed to describe EV production from Candida haemulonii var. vulnera and evaluate whether murine macrophage RAW 264.7 cells respond to their stimuli by generating an oxidative response after 24 h. For this purpose, reactive oxygen species detection assays demonstrated that high concentrations of yeast and EVs (10¹⁰ particles/mL) of Candida haemulonii did not change macrophage viability. However, the macrophages recognized these EVs and triggered an oxidative response through the classical NOX-2 pathway, increasing O₂^•- and H₂O₂ levels. However, this stress did not cause lipid peroxidation in the RAW 264.7 cells and neither lead to the activation of the COX-2-PGE₂ pathway. Thus, our data suggest that low concentrations of C. haemulonii EVs are not recognized by the classical pathway of the oxidative burst generated by macrophages, which might be an advantage allowing the transport of virulence factors via EVs, not identified by the host immune system that could work as fine tube regulators during infections caused by C. haemulonii. In contrast, C. haemulonii var. vulnera and high EV concentrations activated microbicidal actions in macrophages. Therefore, we propose that EVs could participate in the virulence of the species and that these particles could be a source of antigens to be exploited as new therapeutic targets.

Aspergillus fumigatus Extracellular Vesicles Display Increased Galleria mellonella Survival but Partial Pro-Inflammatory Response by Macrophages

Fungal extracellular vesicles (EVs) mediate intra- and interspecies communication and are critical in host-fungus interaction, modulating inflammation and immune responses. In this study, we evaluated the in vitro pro- and anti-inflammatory properties of Aspergillus fumigatus EVs over innate leukocytes. A. fumigatus EVs induced a partial proinflammatory response by macrophages, characterized by increased tumor necrosis factor-alpha production, and increased gene expression of induced nitric oxide synthase and adhesion molecules. EVs induce neither NETosis in human neutrophils nor cytokine secretion by peripheral mononuclear cells. However, prior inoculation of A. fumigatus EVs in Galleria mellonella larvae resulted in increased survival after the fungal challenge. Taken together, these findings show that A. fumigatus EVs play a role in protection against fungal infection, although they induce a partial pro-inflammatory response.

Extracellular Vesicles of the Plant Pathogen Botrytis cinerea

Fungal secretomes are known to contain a multitude of components involved in nutrition, cell growth or biotic interactions. Recently, extra-cellular vesicles have been identified in a few fungal species. Here, we used a multidisciplinary approach to identify and characterize extracellular vesicles produced by the plant necrotroph Botrytis cinerea. Transmission electron microscopy of infectious hyphae and hyphae grown in vitro revealed extracellular vesicles of various sizes and densities. Electron tomography showed the co-existence of ovoid and tubular vesicles and pointed to their release via the fusion of multi-vesicular bodies with the cell plasma membrane. The isolation of these vesicles and exploration of their protein content using mass spectrometry led to the identification of soluble and membrane proteins involved in transport, metabolism, cell wall synthesis and remodeling, proteostasis, oxidoreduction and traffic. Confocal microscopy highlighted the capacity of fluorescently labeled vesicles to target cells of B. cinerea, cells of the fungus Fusarium graminearum, and onion epidermal cells but not yeast cells. In addition, a specific positive effect of these vesicles on the growth of B. cinerea was quantified. Altogether, this study broadens our view on the secretion capacity of B. cinerea and its cell-to-cell communication.

Nanosized extracellular vesicles released by Neurospora crassa hyphae

Extracellular vesicles (EVs) are nanosized structures containing proteins, lipids, and nucleic acids, released by living cells to the surrounding medium. EVs participate in diverse processes, such as intercellular communication, virulence, and disease. In pathogenic fungi, EVs carry enzymes that allow them to invade the host or undergo environmental adaptation successfully. In Neurospora crassa, a non-pathogenic filamentous fungus widely used as a model organism, the vesicle-dependent secretory mechanisms that lead to polarized growth are well studied. In contrast, biosynthesis of EVs in this fungus has been practically unexplored. In the present work, we analyzed N. crassa culture's supernatant for the presence of EVs by dynamic light scattering (DLS), transmission electron microscopy (TEM) and proteomic analysis. We identified spherical membranous structures, with a predominant subpopulation averaging a hydrodynamic diameter (d_h) of 68 nm and a particle diameter (d_p) of 38 nm. EV samples stained with osmium tetroxide vapors were better resolved than those stained with uranyl acetate. Mass spectrometry analysis identified 252 proteins, including enzymes involved in carbohydrate metabolic processes, oxidative stress response, cell wall organization/remodeling, and circadian clock-regulated proteins. Some of these proteins have been previously reported in exosomes from human cells or in EVs of other fungi. In view of the results, it is suggested a putative role for EVs in cell wall biosynthesis and vegetative development in N. crassa.

Bioinformatics strategies for studying the molecular mechanisms of fungal extracellular vesicles with a focus on infection and immune responses

Fungal extracellular vesicles (EVs) are released during pathogenesis and are found to be an opportunistic infection in most cases. EVs are immunocompetent with their host and have paved the way for new biomedical approaches to drug delivery and the treatment of complex diseases including cancer. With computing and processing advancements, the rise of bioinformatics tools for the evaluation of various parameters involved in fungal EVs has blossomed. In this review, we have complied and explored the bioinformatics tools to analyze the host-pathogen interaction, toxicity, omics and pathogenesis with an array of specific tools that have depicted the ability of EVs as vector/carrier for therapeutic agents and as a potential theme for immunotherapy. We have also discussed the generation and pathways involved in the production, transport, pathogenic action and immunological interactions of EVs in the host system. The incorporation of network pharmacology approaches has been discussed regarding fungal pathogens and their significance in drug discovery. To represent the overview, we have presented and demonstrated an in silico study model to portray the human Cryptococcal interactions.

Systems biology-guided understanding of white-rot fungi for biotechnological applications: a review

Plant-derived biomass is the most abundant biogenic carbon source on Earth. Despite this, only a small clade of organisms known as white-rot fungi (WRF) can efficiently break down both the polysaccharide and lignin components of plant cell walls. This unique ability imparts a key role for WRF in global carbon cycling and highlights their potential utilization in diverse biotechnological applications. To date, research on WRF has primarily focused on their extracellular ‘digestive enzymes’ whereas knowledge of their intracellular metabolism remains underexplored. Systems biology is a powerful approach to elucidate biological processes in numerous organisms, including WRF. Thus, here we review systems biology methods applied to WRF to date, highlight observations related to their intracellular metabolism, and conduct comparative extracellular proteomic analyses to establish further correlations between WRF species, enzymes, and cultivation conditions. Lastly, we discuss biotechnological opportunities of WRF as well as challenges and future research directions.

Pathogen-Host Interaction Repertoire at Proteome and Posttranslational Modification Levels During Fungal Infections

Prevalence of fungal diseases has increased globally in recent years, which often associated with increased immunocompromised patients, aging populations, and the novel Coronavirus pandemic. Furthermore, due to the limitation of available antifungal agents mortality and morbidity rates of invasion fungal disease remain stubbornly high, and the emergence of multidrug-resistant fungi exacerbates the problem. Fungal pathogenicity and interactions between fungi and host have been the focus of many studies, as a result, lots of pathogenic mechanisms and fungal virulence factors have been identified. Mass spectrometry (MS)-based proteomics is a novel approach to better understand fungal pathogenicities and host–pathogen interactions at protein and protein posttranslational modification (PTM) levels. The approach has successfully elucidated interactions between pathogens and hosts by examining, for example, samples of fungal cells under different conditions, body fluids from infected patients, and exosomes. Many studies conclude that protein and PTM levels in both pathogens and hosts play important roles in progression of fungal diseases. This review summarizes mass spectrometry studies of protein and PTM levels from perspectives of both pathogens and hosts and provides an integrative conceptual outlook on fungal pathogenesis, antifungal agents development, and host–pathogen interactions.

The multiomics landscape of serum exosomes during the development of sepsis

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The study for the first time describes the profile of molecular dynamics in septic serum exosomes.

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We provide a new direction into proteasome-mediated protein degradation in septic serum exosomes.

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IL-10 delivery by septic exosomes may play a vital role in alleviation of AKI of CLP mice.

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Septic serum exosomes participate in the modulation of sepsis by regulating vitamin metabolism.

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The molecular mechanisms proposed in the study may provide helpful insights for the therapy of sepsis.

Introduction

Sepsis is an infection-induced severe inflammatory disorder leading to multiple organ dysfunction. It remains a highly lethal condition for which early diagnosis and therapy achieve unsatisfactory results. Circulating exosomes containing biomarkers and mediators of sepsis have recently received attention, but the progress has been far from optimal.

Objectives

The present study focuses on the profiles of molecular dynamics in serum exosomes and explores the potential molecular mechanisms on serum exosomes during the process of sepsis.

Methods

We used high-performance liquid chromatography-tandem mass spectrometry and RNA-seq to detect the dynamic profiles of exosome proteins and RNAs (including mRNAs, lncRNAs and miRNAs) in serum exosomes from 3 healthy individuals and 9 septic patients at the different stages. Then integrative multiomics analyses were performed and the results were validated by qRT-PCR, LiquiChip assay and metabolomics analysis on mice subjected to cecal ligation and puncture (CLP) modeling.

Results

A total of 354 proteins, 195 mRNAs, 82 lncRNAs and 55 miRNAs were identified as differentially expressed molecules in serum exosomes from septic patients. Integrative multiomics analysis showed that exosome components were associated with cytokine storm, complement and clotting cascades, the endothelial barrier, 20S proteasome-dependent protein degradation and vitamin metabolism. Importantly, pretreatment with serum exosomes derived from mice subjected to CLP significantly restrained proinflammatory cytokine expression and alleviated tissue injury in septic mice. Further metabolomics analysis demonstrated that pretreatment with septic serum exosomes significantly affected the metabolites associated with vitamin digestion and absorption in CLP mice.

Conclusion

Our study for the first time describes the landscape of the molecular dynamics of serum exosomes during the development of sepsis and proposes some hypothetical molecular mechanisms by integrative multiomics analysis, which may provide helpful diagnostic and therapeutic insights for the ongoing battle against sepsis.

Communication is key: Extracellular vesicles as mediators of infection and defence during host-microbe interactions in animals and plants

Extracellular vesicles (EVs) are now understood to be ubiquitous mediators of cellular communication. In this review, we suggest that EVs have evolved into a highly regulated system of communication with complex functions including export of wastes, toxins and nutrients, targeted delivery of immune effectors and vectors of RNA silencing. Eukaryotic EVs come in different shapes and sizes and have been classified according to their biogenesis and size distributions. Small EVs (or exosomes) are released through fusion of endosome-derived multivesicular bodies with the plasma membrane. Medium EVs (or microvesicles) bud off the plasma membrane as a form of exocytosis. Finally, large EVs (or apoptotic bodies) are produced as a result of the apoptotic process. This review considers EV secretion and uptake in four eukaryotic kingdoms, three of which produce cell walls. The impacts cell walls have on EVs in plants and fungi are discussed, as are roles of fungal EVs in virulence. Contributions of plant EVs to development and innate immunity are presented. Compelling cases are sporophytic self-incompatibility and cellular invasion by haustorium-forming filamentous pathogens. The involvement of EVs in all of these eukaryotic processes is reconciled considering their evolutionary history.

Cryptococcus extracellular vesicles properties and their use as vaccine platforms

Whereas extracellular vesicle (EV) research has become commonplace in different biomedical fields, this field of research is still in its infancy in mycology. Here we provide a robust set of data regarding the structural and compositional aspects of EVs isolated from the fungal pathogenic species Cryptococcus neoformans, C. deneoformans and C. deuterogattii. Using cutting-edge methodological approaches including cryogenic electron microscopy and cryogenic electron tomography, proteomics, and flow cytometry, we revisited cryptococcal EV features and suggest a new EV structural model, in which the vesicular lipid bilayer is covered by mannoprotein-based fibrillar decoration, bearing the capsule polysaccharide as its outer layer. About 10% of the EV population is devoid of fibrillar decoration, adding another aspect to EV diversity. By analysing EV protein cargo from the three species, we characterized the typical Cryptococcus EV proteome. It contains several membrane-bound protein families, including some Tsh proteins bearing a SUR7/PalI motif. The presence of known protective antigens on the surface of Cryptococcus EVs, resembling the morphology of encapsulated virus structures, suggested their potential as a vaccine. Indeed, mice immunized with EVs obtained from an acapsular C. neoformans mutant strain rendered a strong antibody response in mice and significantly prolonged their survival upon C. neoformans infection.

Turning Inside Out: Filamentous Fungal Secretion and Its Applications in Biotechnology, Agriculture, and the Clinic

Filamentous fungi are found in virtually every marine and terrestrial habitat. Vital to this success is their ability to secrete a diverse range of molecules, including hydrolytic enzymes, organic acids, and small molecular weight natural products. Industrial biotechnologists have successfully harnessed and re-engineered the secretory capacity of dozens of filamentous fungal species to make a diverse portfolio of useful molecules. The study of fungal secretion outside fermenters, e.g., during host infection or in mixed microbial communities, has also led to the development of novel and emerging technological breakthroughs, ranging from ultra-sensitive biosensors of fungal disease to the efficient bioremediation of polluted environments. In this review, we consider filamentous fungal secretion across multiple disciplinary boundaries (e.g., white, green, and red biotechnology) and product classes (protein, organic acid, and secondary metabolite). We summarize the mechanistic understanding for how various molecules are secreted and present numerous applications for extracellular products. Additionally, we discuss how the control of secretory pathways and the polar growth of filamentous hyphae can be utilized in diverse settings, including industrial biotechnology, agriculture, and the clinic.

RNAs on the Go: Extracellular Transfer in Insects with Promising Prospects for Pest Management

RNA-mediated pathways form an important regulatory layer of myriad biological processes. In the last decade, the potential of RNA molecules to contribute to the control of agricultural pests has not been disregarded, specifically via the RNA interference (RNAi) mechanism. In fact, several proofs-of-concept have been made in this scope. Furthermore, a novel research field regarding extracellular RNAs and RNA-based intercellular/interorganismal communication is booming. In this article, we review key discoveries concerning extracellular RNAs in insects, insect RNA-based cell-to-cell communication, and plant-insect transfer of RNA. In addition, we overview the molecular mechanisms implicated in this form of communication and discuss future biotechnological prospects, namely from the insect pest-control perspective.

Vaccines for human fungal diseases: close but still a long way to go

Despite the substantial global burden of human fungal infections, there are no approved fungal vaccines to protect at risk individuals. Here, we review the progress that has been made and the challenges that lie ahead in the quest towards efficacious fungal vaccines. In mouse studies, protection has been achieved with vaccines directed against fungal pathogens, including species of Candida, Cryptococcus, and Aspergillus, that most commonly cause life-threatening human disease. Encouraging results have been obtained with vaccines composed of live-attenuated and killed fungi, crude extracts, recombinant subunit formulations, and nucleic acid vaccines. Novel adjuvants that instruct the immune system to mount the types of protective responses needed to fight mycotic infections are under development. Candidate vaccines include those that target common antigens expressed on multiple genera of fungi thereby protecting against a broad range of mycoses. Encouragingly, three vaccines have reached human clinical trials. Still, formidable obstacles must be overcome before we will have fungal vaccines licensed for human use.

Through the back door: Unconventional protein secretion

Proteins are secreted from eukaryotic cells by several mechanisms besides the well-characterized classical secretory system. Proteins destined to enter the classical secretory system contain a signal peptide for translocation into the endoplasmic reticulum. However, many proteins lacking a signal peptide are secreted nonetheless. Contrary to conventional belief, these proteins are not just released as a result of membrane damage leading to cell leakage, but are actively packaged for secretion in alternative pathways. They are called unconventionally secreted proteins, and the best-characterized are from fungi and mammals. These proteins have extracellular functions including cell signaling, immune modulation, as well as moonlighting activities different from their well-described intracellular functions. Among the pathways for unconventional secretion are direct transfer across the plasma membrane, release within plasma membrane-derived microvesicles, use of elements of autophagy, or secretion from endosomal/multivesicular body-related components. We review the fungal and metazoan unconventional secretory pathways and their regulation, and propose experimental criteria to identify their mode of secretion.

Extracellular vesicles from the apoplastic fungal wheat pathogen Zymoseptoria tritici

BACKGROUND

The fungal pathogen Zymoseptoria tritici is a significant constraint to wheat production in temperate cropping regions around the world. Despite its agronomic impacts, the mechanisms allowing the pathogen to asymptomatically invade and grow in the apoplast of wheat leaves before causing extensive host cell death remain elusive. Given recent evidence of extracellular vesicles (EVs)-secreted, membrane-bound nanoparticles containing molecular cargo-being implicated in extracellular communication between plants and fungal pathogen, we have initiated an in vitro investigation of EVs from this apoplastic fungal wheat pathogen. We aimed to isolate EVs from Z. tritici broth cultures and examine their protein composition in relation to the soluble protein in the culture filtrate and to existing fungal EV proteomes.

RESULTS

Zymoseptoria tritici EVs were isolated from broth culture filtrates using differential ultracentrifugation (DUC) and examined with transmission electron microscopy (TEM) and nanoparticle tracking analysis (NTA). Z. tritici EVs were observed as a heterogeneous population of particles, with most between 50 and 250 nm. These particles were found in abundance in the culture filtrates of viable Z. tritici cultures, but not heat-killed cultures incubated for an equivalent time and of comparable biomass. Bottom-up proteomic analysis using LC-MS/MS, followed by stringent filtering revealed 240 Z. tritici EV proteins. These proteins were distinct from soluble proteins identified in Z. tritici culture filtrates, but were similar to proteins identified in EVs from other fungi, based on sequence similarity analyses. Notably, a putative marker protein recently identified in Candida albicans EVs was also consistently detected in Z. tritici EVs.

CONCLUSION

We have shown EVs can be isolated from the devastating fungal wheat pathogen Z. tritici and are similar to protein composition to previously characterised fungal EVs. EVs from human pathogenic fungi are implicated in virulence, but the role of EVs in the interaction of phytopathogenic fungi and their hosts is unknown. These in vitro analyses provide a basis for expanding investigations of Z. tritici EVs in planta, to examine their involvement in the infection process of this apoplastic wheat pathogen and more broadly, advance understanding of noncanonical secretion in filamentous plant pathogens.

Extracellular Vesicles: New Bullets to Fight Fungal Infections

While behaving as a commensal yeast in healthy people, Candida albicans remains the deadliest fungal pathogen in immunocompromised patients. Halder et al. deciphered unprecedented immunomodulatory properties of monocyte extracellular vesicles in response to Candida infections, paving the way to consider therapeutic innovations for fungal infections but also inflammatory diseases.

Characteristics of Extracellular Vesicles Released by the Pathogenic Yeast-Like Fungi Candida glabrata, Candida parapsilosis and Candida tropicalis

Candida spp. yeast-like fungi are opportunistic pathogens in humans and have been recently found to release extracellular vesicles (EVs) that are involved in many vital biological processes in fungal cells. These include communication between microorganisms and host–pathogen interactions during infection. The production of EVs and their content have been significantly characterized in the most common candidal species Candida albicans, including the identification of numerous virulence factors and cytoplasmic proteins in the EV cargo. We have here conducted the isolation and proteomic characterization of EVs produced by the clinically important non-albicans Candida species C. glabrata, C. tropicalis and C. parapsilosis. With the use of ultracentrifugation of the cell-free culture supernatant, the candidal EVs were collected and found to be a heterogeneous population of particles for each species with sizes ranging from 60–280 nm. The proteinaceous contents of these vesicles were analyzed using LC-MS/MS, with particular attention paid to surface-expressed proteins that would come into immediate and direct contact with host cells. We thereby identified 42 extracellular and surface-connected proteins from C. glabrata, 33 from C. parapsilosis, and 34 from C. tropicalis, including membrane-associated transporters, glycoproteins and enzymes involved in the organization of the fungal cell wall, as well as several cytoplasmic proteins, including alcohol dehydrogenase, enolase, glyceraldehyde-3-phosphate dehydrogenase, phosphoglycerate kinase and pyruvate kinase, for which the vesicular transport is a possible mechanism underlying their non-classical secretion.

Extracellular Vesicles in Fungi: Past, Present, and Future Perspectives

Extracellular vesicles (EVs) have garnered much interest in the cell biology and biomedical research fields. Many studies have reported the existence of EVs in all types of living cells, including in fifteen different fungal genera. EVs play diverse biological roles, from the regulation of physiological events and response to specific environmental conditions to the mediation of highly complex interkingdom communications. This review will provide a historical perspective on EVs produced by fungi and an overview of the recent discoveries in the field. We will also review the current knowledge about EV biogenesis and cargo, their role in cell-to-cell interactions, and methods of EV analysis. Finally, we will discuss the perspectives of EVs as vehicles for the delivery of biologically active molecules.

The Neurotropic Black Yeast Exophiala dermatitidis Induces Neurocytotoxicity in Neuroblastoma Cells and Progressive Cell Death

The neurotropic and extremophilic black yeast Exophiala dermatitidis (Herpotrichellaceae) inhabits diverse indoor environments, in particular bathrooms, steam baths, and dishwashers. Here, we show that the selected strain, EXF-10123, is polymorphic, can grow at 37 °C, is able to assimilate aromatic hydrocarbons (toluene, mineral oil, n-hexadecane), and shows abundant growth with selected neurotransmitters (acetylcholine, gamma-aminobutyric acid, glycine, glutamate, and dopamine) as sole carbon sources. We have for the first time demonstrated the effect of E. dermatitidis on neuroblastoma cell model SH-SY5Y. Aqueous and organic extracts of E. dermatitidis biomass reduced SH-SY5Y viability by 51% and 37%, respectively. Melanized extracellular vesicles (EVs) prepared from this strain reduced viability of the SH-SY5Y to 21%, while non-melanized EVs were considerably less neurotoxic (79% viability). We also demonstrated direct interactions of E. dermatitidis with SH-SY5Y by scanning electron and confocal fluorescence microscopy. The observed invasion and penetration of neuroblastoma cells by E. dermatitidis hyphae presumably causes the degradation of most neuroblastoma cells in only three days. This may represent a so far unknown indirect or direct cause for the development of some neurodegenerative diseases such as Alzheimer’s.

Erg6 affects membrane composition and virulence of the human fungal pathogen Cryptococcus neoformans

Ergosterol is the most important membrane sterol in fungal cells and a component not found in the membranes of human cells. We identified the ERG6 gene in the AIDS-associated fungal pathogen, Cryptococcus neoformans, encoding the sterol C-24 methyltransferase of fungal ergosterol biosynthesis. In this work, we have explored its relationship with high-temperature growth and virulence of C. neoformans by the construction of a loss-of-function mutant. In contrast to other genes involved in ergosterol biosynthesis, C. neoformans ERG6 is not essential for growth under permissive conditions in vitro. However, the erg6 mutant displayed impaired thermotolerance and increased susceptibility to osmotic and oxidative stress, as well as to different antifungal drugs. Total lipid analysis demonstrated a decrease in the erg6Δ strain membrane ergosterol content. In addition, this mutant strain was avirulent in an invertebrate model of C. neoformans infection. C. neoformans Erg6 was cyto-localized in the endoplasmic reticulum and Golgi complex. Our results demonstrate that Erg6 is crucial for growth at high temperature and virulence, likely due to its effects on C. neoformans membrane integrity and dynamics. These pathogen-focused investigations into ergosterol biosynthetic pathway components reinforce the multiple roles of ergosterol in the response of diverse fungal species to alterations in the environment, especially that of the infected host. These studies open perspectives to understand the participation of ergosterol in mechanism of resistance to azole and polyene drugs. Observed synergistic growth defects with co-inhibition of Erg6 and other components of the ergosterol biosynthesis pathway suggests novel approaches to treatment in human fungal infections.

Extracellular Vesicles Released From the Skin Commensal Yeast Malassezia sympodialis Activate Human Primary Keratinocytes

Extracellular vesicles (EVs) released from fungi have been shown to participate in inter-organismal communication and in cross-kingdom modulation of host defense. Malassezia species are the dominant commensal fungal members of the human skin microbiota. We have previously found that Malassezia sympodialis releases EVs. These EVs, designated MalaEx, carry M. sympodialis allergens and induce a different inflammatory cytokine response in peripheral blood mononuclear cells (PBMC) from patients with atopic dermatitis compared to healthy controls. In this study, we explored the host-microbe interaction between MalaEx and human keratinocytes with the hypothesis that MalaEx might be able to activate human keratinocytes to express the intercellular adhesion molecule-1 (ICAM-1, CD54). MalaEx were prepared from M. sympodialis (ATCC 42132) culture supernatants by a combination of centrifugation, filtration and serial ultracentrifugation. The MalaEx showed a size range of 70–580 nm with a mean of 154 nm using nanoparticle tracking analysis. MalaEx were found to induce a significant up-regulation of ICAM-1 expression on primary human keratinocytes isolated from human ex vivo skin (p = 0.026, n = 3), compared to the unstimulated keratinocytes. ICAM-1 is a counter ligand for the leukocyte integrins lymphocyte function-associated antigen-1 (LFA-1) and macrophage-1 antigen (Mac-1), of which induced expression on epithelial cells leads to the attraction of immune competent cells. Thus, the capacity of MalaEx to activate keratinocytes with an enhanced ICAM-1 expression indicates an important step in the cutaneous defense against M. sympodialis. How this modulation of host cells by a fungus is balanced between the commensal, pathogenic, or beneficial states on the skin in the interplay with the host needs to be further elucidated.

Extracellular vesicles in host-pathogen interactions and immune regulation - exosomes as emerging actors in the immunological theater of pregnancy

This review correlates and summarizes the role of the maternal-fetal interface in the immune tolerance of the fetus and the processes that lead to infection avoidance, emphasizing the participation of exosomes and other extracellular vesicles in both situations. Exosomes are released into the extracellular medium by several cell types and are excellent carriers of biomolecules. Host-derived exosomes and the transport of pathogen-derived molecules by exosomes impact infections in different ways. The interactions of exosomes with the maternal immune system are pivotal to a favorable gestational outcome. In this review, we highlight the potential role of exosomes in the establishment of an adequate milieu that enables embryo implantation and discuss the participation of exosomes released at the maternal-fetal interface during the establishment of an immune-privileged compartment for fetal development. The placenta is a component where important strategies are used to minimize the risk of infection. To present a contrast, we also discuss possible mechanisms used by pathogens to cross the maternal-fetal interface. We review the processes, mechanisms, and potential consequences of dysregulation in all of the abovementioned phenomena. Basic information about exosomes and their roles in viral immune evasion is also presented. The interactions between extracellular vesicles and bacteria, fungi, parasites and proteinaceous infectious agents are addressed. The discovery of the placental microbiota and the implications of this new microbiota are also discussed, and current proposals that explain fetal/placental colonization by both pathogenic and commensal microbes are addressed. The comprehension of such interactions will help us to understand the immune dynamics of human pregnancy and the mechanisms of immune evasion used by different pathogens.

Extracellular Vesicles From the Cotton Pathogen Fusarium oxysporum f. sp. vasinfectum Induce a Phytotoxic Response in Plants

Extracellular vesicles (EVs) represent a system for the coordinated secretion of a variety of molecular cargo including proteins, lipids, nucleic acids, and metabolites. They have an essential role in intercellular communication in multicellular organisms and have more recently been implicated in host-pathogen interactions. Study of the role for EVs in fungal biology has focused on pathogenic yeasts that are major pathogens in humans. In this study we have expanded the investigation of fungal EVs to plant pathogens, specifically the major cotton pathogen Fusarium oxysporum f. sp. vasinfectum. EVs isolated from F. oxysporum f. sp. vasinfectum culture medium have a morphology and size distribution similar to EVs from yeasts such as Candida albicans and Cryptococcus neoformans. A unique feature of the EVs from F. oxysporum f. sp. vasinfectum is their purple color, which is predicted to arise from a napthoquinone pigment being packaged into the EVs. Proteomic analysis of F. oxysporum f. sp. vasinfectum EVs revealed that they are enriched in proteins that function in synthesis of polyketides as well as proteases and proteins that function in basic cellular processes. Infiltration of F. oxysporum f. sp. vasinfectum EVs into the leaves of cotton or N. benthamiana plants led to a phytotoxic response. These observations lead to the hypothesis that F. oxysporum f. sp. vasinfectum EVs are likely to play a crucial role in the infection process.