Calcium regulates in vitro dimorphism in chromoblastomycotic fungi

Pathogenicity and Growth Conditions Modulate Fonsecaea Extracellular Vesicles' Ability to Interact With Macrophages

Chromoblastomycosis (CBM) is a chronic cutaneous and subcutaneous mycosis caused by black, dimorphic, and filamentous fungi of the Herpothrichiellaceae family, such as species of the genus Fonsecaea. These fungi can switch between the saprophytic forms (conidia and hyphae) and the pathogenic form, the muriform cells (MCs), which is considered an essential mechanism for fungal virulence. Nearly all types of cells can produce membranous structures formed by a lipid bilayer that communicate extracellularly with other cells, known as "extracellular vesicles" (EVs), which may act as virulence factors, as observed for several species of pathogenic fungi. Our findings demonstrated for the first time that F. pedrosoi, F. nubica, and F. erecta produce EVs in response to nutritional conditions. The EVs varied in sterol and protein contents, size, and morphology. Moreover, the EVs induced different cytokine and nitric oxide release patterns by bone marrow-derived macrophages (BMDMs). The EVs activated IL-1β production, possibly acting as the first signal in inflammasome activation. Unlike the pathogenic species, the EVs isolated from F. erecta did not significantly stimulate TNF and IL-10 production in general. Overall, these results demonstrated that different species of Fonsecaea produce EVs capable of modulating pro- and anti-inflammatory cytokine and nitric oxide production by BMDMs and that growth conditions affected the immunomodulatory capacities of the EVs as well as their size, content, and morphology.

Unique functional responses of fungal communities to various environments in the mangroves of the Maowei Sea in Guangxi, China

Fungi are important compartments of microbial communities of mangroves. Their diversity might be influenced by their habitat environment. This study analyzed the distribution and function of fungal communities in the sediments and plant samples from mangrove ecosystem of the Maowei Sea area in Guangxi, China. The results showed that phytopathogenic fungi Cladosporium (17.00%) was mainly observed in the sediments from the protected zone, while endophytic fungi Alternaria (9.22%) and Acremonium (6.09%) were only observed in the sediments from wharf. The fungi in the sediments from village and park were mainly consisted of high-activity endophytes and fungi related to lignin-degrading, respectively. Acaulospora and Aspergillus with higher relative abundance discovered in plant tissues could help plant growth. Cirrenalia (37.66%) and Lignincola (26.73%) with high-activity for lignin-degrading were discovered in decayed leaves. The distribution and function of fungi were highly dependent on the environment settings, thus the fungi can be used as indicators for monitoring the environmental change of mangrove ecosystems.

Melanin and chromoblastomycosis agents: Characterization, functions, and relation with antifungals

Melanins are a diverse group of dark pigments with similar properties. In fungi, the most studied is the dihydroxynaphtalene (DHN)-melanin, present in several species including all the chromoblastomycosis agents, a chronic, disabling, and recalcitrant subcutaneous mycosis. It is synthesized in a pathway known as the pentaketide pathway, which has the agrochemical tricyclazole as an inhibitor, widely used in in vitro studies because it does not prevent the growth of fungi. There are different methodologies for qualitative and quantitative analyses of DHN-melanin, which made it possible to discover its important structural and antioxidant functions, with melanin acting as a protective factor against the host's immune system. Also, it can interact with some of the main antifungals of medical interest, reducing its activity and the susceptibility of fungi to these agents. This review aims to discuss the aspects of DHN-melanin, focusing on chromoblastomycosis, bringing the main findings of the published scientific studies, and highlighting the need for further research to understand this important fungal pathogenicity and a virulence factor.

Molecular identification and antifungal susceptibility profiles of clinical strains of Fonsecaea spp. isolated from patients with chromoblastomycosis in Rio de Janeiro, Brazil

BACKGROUND

Chromoblastomycosis (CBM) is a difficult-to-treat chronic subcutaneous mycosis. In Brazil, the main agent of this disease is Fonsecaea pedrosoi, which is phenotypically very similar to other Fonsecaea species, differing only genetically. The correct species identification is relevant since different species may differ in their epidemiologic aspects, clinical presentation, and treatment response.

METHODOLOGY/PRINCIPAL FINDINGS

Partial sequencing of the internal transcribed spacer (ITS) was used to identify twenty clinical isolates of Fonsecaea spp. Their in vitro antifungal susceptibility was determined using the broth microdilution method, according to the M38-A2 protocol. Amphotericin B (AMB), flucytosine (5FC), terbinafine (TRB), fluconazole (FLC), itraconazole (ITC), ketoconazole (KTC), posaconazole (POS), voriconazole (VRC), ravuconazole (RVC), caspofungin (CAS), and micafungin (MFG) were tested. The association between ITC/TRB, AMB/5FC, and ITC/CAS was studied by the checkerboard method to check synergism. The available patients' data were correlated with the obtained laboratory results. Fonsecaea monophora (n = 10), F. pedrosoi (n = 5), and F. nubica (n = 5) were identified as CBM' agents in the study. TRB and VRC were the drugs with the best in vitro activity with minimal inhibitory concentrations (MIC) lower than 0.25 mg/L. On the other hand, FLC, 5FC, AMB, and MFG showed high MICs. The AMB/5FC combination was synergistic for three F. monophora strains while the others were indifferent. Patients had moderate or severe CBM, and ITC therapy was not sufficient for complete cure in most of the cases, requiring adjuvant surgical approaches.

CONCLUSIONS/SIGNIFICANCE

F. monophora, the second most frequent Fonsecaea species in South America, predominated in patients raised and born in Rio de Janeiro, Brazil, without cerebral involvement in these cases. TRB, VRC, and the AMB/5FC combination should be further investigated as a treatment option for CBM.

Fonsecaea pedrosoi Sclerotic Cells: Secretion of Aspartic-Type Peptidase and Susceptibility to Peptidase Inhibitors

Fonsecaea pedrosoi is a dematiaceous fungus and the main causative agent of chromoblastomycosis that is a chronic disease usually affecting the human skin and subcutaneous tissues, which causes deformations and incapacities, being frequently refractory to available therapies. A typical globe-shaped, multiseptated and pigmented cells, known as sclerotic cells, are found in the lesions of infected individuals. In the present work, we have investigated the production of aspartic-type peptidase in F. pedrosoi sclerotic cells as well as the effect of peptidase inhibitors (PIs) on its enzymatic activity and viability. Our data showed that sclerotic cells are able to secrete pepstatin A-sensible aspartic peptidase when grown under chemically defined conditions. In addition, aspartic PIs (ritonavir, nelfinavir, indinavir, and saquinavir), which are clinically used in the HIV chemotherapy, significantly decreased the fungal peptidase activity, varying from 55 to 99%. Moreover, sclerotic cell-derived aspartic peptidase hydrolyzed human albumin, an important serum protein, as well as laminin, an extracellular matrix component, but not immunoglobulin G and fibronectin. It is well-known that aspartic peptidases play important physiological roles in fungal cells. With this task in mind, the effect of pepstatin A, a classical aspartic peptidase inhibitor, on the F. pedrosoi proliferation was evaluated. Pepstatin A inhibited the fungal viability in both cellular density- and drug-concentration manners. Moreover, HIV-PIs at 10 μM powerfully inhibited the viability (>65%) of F. pedrosoi sclerotic cells. The detection of aspartic peptidase produced by sclerotic cells, the parasitic form of F. pedrosoi, may contribute to reveal new virulence markers and potential targets for chromoblastomycosis therapy.

Chromoblastomycosis

Chromoblastomycosis (CBM), also known as chromomycosis, is one of the most prevalent implantation fungal infections, being the most common of the gamut of mycoses caused by melanized or brown-pigmented fungi. CBM is mainly a tropical or subtropical disease that may affect individuals with certain risk factors around the world. The following characteristics are associated with this disease: (i) traumatic inoculation by implantation from an environmental source, leading to an initial cutaneous lesion at the inoculation site; (ii) chronic and progressive cutaneous and subcutaneous tissular involvement associated with fibrotic and granulomatous reactions associated with microabscesses and often with tissue proliferation; (iii) a nonprotective T helper type 2 (Th2) immune response with ineffective humoral involvement; and (iv) the presence of muriform (sclerotic) cells embedded in the affected tissue. CBM lesions are clinically polymorphic and are commonly misdiagnosed as various other infectious and noninfectious diseases. In its more severe clinical forms, CBM may cause an incapacity for labor due to fibrotic sequelae and also due to a series of clinical complications, and if not recognized at an early stage, this disease can be refractory to antifungal therapy.

Exploring the genomic diversity of black yeasts and relatives (Chaetothyriales, Ascomycota)

The order Chaetothyriales (Pezizomycotina, Ascomycetes) harbours obligatorily melanised fungi and includes numerous etiologic agents of chromoblastomycosis, phaeohyphomycosis and other diseases of vertebrate hosts. Diseases range from mild cutaneous to fatal cerebral or disseminated infections and affect humans and cold-blooded animals globally. In addition, Chaetothyriales comprise species with aquatic, rock-inhabiting, ant-associated, and mycoparasitic life-styles, as well as species that tolerate toxic compounds, suggesting a high degree of versatile extremotolerance. To understand their biology and divergent niche occupation, we sequenced and annotated a set of 23 genomes of main the human opportunists within the Chaetothyriales as well as related environmental species. Our analyses included fungi with diverse life-styles, namely opportunistic pathogens and closely related saprobes, to identify genomic adaptations related to pathogenesis. Furthermore, ecological preferences of Chaetothyriales were analysed, in conjuncture with the order-level phylogeny based on conserved ribosomal genes. General characteristics, phylogenomic relationships, transposable elements, sex-related genes, protein family evolution, genes related to protein degradation (MEROPS), carbohydrate-active enzymes (CAZymes), melanin synthesis and secondary metabolism were investigated and compared between species. Genome assemblies varied from 25.81 Mb (Capronia coronata) to 43.03 Mb (Cladophialophora immunda). The bantiana-clade contained the highest number of predicted genes (12 817 on average) as well as larger genomes. We found a low content of mobile elements, with DNA transposons from Tc1/Mariner superfamily being the most abundant across analysed species. Additionally, we identified a reduction of carbohydrate degrading enzymes, specifically many of the Glycosyl Hydrolase (GH) class, while most of the Pectin Lyase (PL) genes were lost in etiological agents of chromoblastomycosis and phaeohyphomycosis. An expansion was found in protein degrading peptidase enzyme families S12 (serine-type D-Ala-D-Ala carboxypeptidases) and M38 (isoaspartyl dipeptidases). Based on genomic information, a wide range of abilities of melanin biosynthesis was revealed; genes related to metabolically distinct DHN, DOPA and pyomelanin pathways were identified. The MAT (MAting Type) locus and other sex-related genes were recognized in all 23 black fungi. Members of the asexual genera Fonsecaea and Cladophialophora appear to be heterothallic with a single copy of either MAT-1-1 or MAT-1-2 in each individual. All Capronia species are homothallic as both MAT1-1 and MAT1-2 genes were found in each single genome. The genomic synteny of the MAT-locus flanking genes (SLA2-APN2-COX13) is not conserved in black fungi as is commonly observed in Eurotiomycetes, indicating a unique genomic context for MAT in those species. The heterokaryon (het) genes expansion associated with the low selective pressure at the MAT-locus suggests that a parasexual cycle may play an important role in generating diversity among those fungi.

1,10-Phenanthroline-5,6-Dione-Based Compounds Are Effective in Disturbing Crucial Physiological Events of Phialophora verrucosa

Phialophora verrucosa is a dematiaceous fungus able to cause chromoblastomycosis, phaeohyphomycosis and mycetoma. All these fungal diseases are extremely difficult to treat and often refractory to the current therapeutic approaches. Therefore, there is an urgent necessity to develop new antifungal agents to combat these mycoses. In this context, the aim of the present work was to investigate the effect of 1,10-phenanthroline-5,6-dione (phendione) and its metal-based derivatives [Ag(phendione)₂]ClO₄ = ([Ag(phendione)₂]⁺) and [Cu(phendione)₃](ClO₄)₂.4H₂O = ([Cu(phendione)₃]²⁺) on crucial physiological events of P. verrucosa conidial cells. Using the CLSI protocol, we have shown that phendione, [Ag(phendione)₂]⁺ and [Cu(phendione)₃]²⁺ were able to inhibit fungal proliferation, presenting MIC/IC₅₀ values of 12.0/7.0, 4.0/2.4, and 5.0/1.8 μM, respectively. [Cu(phendione)₃]²⁺ had fungicidal action and when combined with amphotericin B, both at sub-MIC (½ × MIC) concentrations, significantly reduced (~40%) the fungal growth. Cell morphology changes inflicted by phendione and its metal-based derivatives was corroborated by scanning electron microscopy, which revealed irreversible ultrastructural changes like surface invaginations, cell disruption and shrinkages. Furthermore, [Cu(phendione)₃]²⁺ and [Ag(phendione)₂]⁺ were able to inhibit metallopeptidase activity secreted by P. verrucosa conidia by approximately 85 and 40%, respectively. Ergosterol content was reduced (~50%) after the treatment of P. verrucosa conidial cells with both phendione and [Ag(phendione)₂]⁺. To different degrees, all of the test compounds were able to disturb the P. verrucosa conidia-into-mycelia transformation. Phendione and its Ag⁺ and Cu²⁺ complexes may represent a promising new group of antimicrobial agents effective at inhibiting P. verrucosa growth and morphogenesis.

Black yeasts and their filamentous relatives: principles of pathogenesis and host defense

Among the melanized fungi, the so-called "black yeasts" and their filamentous relatives are particularly significant as agents of severe phaeohyphomycosis, chromoblastomycosis, and mycetoma in humans and animals. The pathogenicity and virulence of these fungi may differ significantly between closely related species. The factors which probably are of significance for pathogenicity include the presence of melanin and carotene, formation of thick cell walls and meristematic growth, presence of yeast-like phases, thermo- and perhaps also osmotolerance, adhesion, hydrophobicity, assimilation of aromatic hydrocarbons, and production of siderophores. Host defense has been shown to rely mainly on the ingestion and elimination of fungal cells by cells of the innate immune system, especially neutrophils and macrophages. However, there is increasing evidence supporting a role of T-cell-mediated immune responses, with increased interleukin-10 (IL-10) and low levels of gamma interferon (IFN-γ) being deleterious during the infection. There are no standardized therapies for treatment. It is therefore important to obtain in vitro susceptibilities of individual patients' fungal isolates in order to provide useful information for selection of appropriate treatment protocols. This article discusses the pathogenesis and host defense factors for these fungi and their severity, chronicity, and subsequent impact on treatment and prevention of diseases in human or animal hosts.

Black Molds and Melanized Yeasts Pathogenic to Humans

A review is given of melanized fungi involved in human infection, including species forming budding cells and strictly filamentous representatives. Classically, they are known as "phaeoid" or "dematiaceous" fungi, and, today, agents are recognized to belong to seven orders of fungi, of which the Chaetothyriales and Pleosporales are the most important. Infections range from cutaneous or pulmonary colonization to systemic or disseminated invasion. Subcutaneous involvement, either primary or after dissemination, may lead to host tissue proliferation of dermis or epidermis. Particularly in the Chaetothyriales, subcutaneous and systemic infections may occur in otherwise apparently healthy individuals. Infections are mostly chronic and require extended antifungal therapy and/or surgery.

Local phagocytic responses after murine infection with different forms of Fonsecaea pedrosoi and sclerotic bodies originating from an inoculum of conidiogenous cells

Fonsecaea pedrosoi is an important causative agent of chromoblastomycosis (CBM) especially in humid areas of the world; however, little is known about the infective forms of this agent that cause CBM. The aim of this study was to investigate the murine tissue response to inoculation with different forms of F. pedrosoi and the morphological changes of the fungal cells in vivo. BALB/c mice were inoculated intraperitoneally with hyphae, conidia or conidiogenous cells and conidia (CCC) at a single site. In addition, the abdomen and footpads were infected subcutaneously with CCC. Fungal forms were inoculated at a final concentration of 1 × 10(6) cells. Hyphae and ungerminated conidia inocula could not be transformed into parasitic forms. In tissue, a great number of conidiogenous cells underwent transformation into sclerotic bodies, which were more resistant to phagocytes in vivo than conidia and hyphae. Clinical and mycological cure of animals infected with CCC was observed from the fourth to the sixth week of infection, while conidia and hyphae infections were faster and generally lasted 2 to 3 weeks. A high number of destructed conidia was observed intracellularly in macrophages. The migration of neutrophils to the inflammatory site seems important for microbicidal activity, particularly against hyphae. Our observations suggest that inocula with conidiogenous cells are associated with in vivo transformation into sclerotic bodies and that local immune response involved with host resistance to experimental F. pedrosoi-infection is primarily mediated by neutrophils as observed in histological sections.

Evolution of CDC42, a putative virulence factor triggering meristematic growth in black yeasts

The cell division cycle gene (CDC42) controlling cellular polarization was studied in members of Chaetothyriales. Based on ribosomal genes, ancestral members of the order exhibit meristematic growth in view of their colonization of inert surfaces such as rock, whereas in derived members of the order the gene is a putative virulence factor involved in expression of the muriform cell, the invasive phase in human chromoblastomycosis. Specific primers were developed to amplify a portion of the gene of 32 members of the order with known position according to ribosomal phylogeny. Phylogeny of CDC42 proved to be very different. In all members of Chaetohyriales the protein sequence is highly conserved. In most species, distributed all over the phylogenetic tree, introns and 3^rd codon positions are also invariant. However, a number of species had paralogues with considerable deviation in non-coding exon positions, and synchronous variation in introns, although non-synonomous variation had remained very limited. In some strains both orthologues and paralogues were present. It is concluded that CDC42 does not show any orthologous evolution, and that its paralogues haves the same function but are structurally relaxed. The variation or absence thereof could not be linked to ecological changes, from rock-inhabiting to pathogenic life style. It is concluded that eventual pathogenicity in Chaetothyriales is not expressed at the DNA level in CDC42 evolution.

Drought meets acid: three new genera in a dothidealean clade of extremotolerant fungi

Fungal strains isolated from rocks and lichens collected in the Antarctic ice-free area of the Victoria Land, one of the coldest and driest habitats on earth, were found in two phylogenetically isolated positions within the subclass Dothideomycetidae. They are here reported as new genera and species, Recurvomyces mirabilisgen. nov., sp. nov. and Elasticomyces elasticusgen. nov., sp. nov. The nearest neighbours within the clades were other rock-inhabiting fungi from dry environments, either cold or hot. Plant-associated Mycosphaerella-like species, known as invaders of leathery leaves in semi-arid climates, are also phylogenetically related with the new taxa. The clusters are also related to the halophilic species Hortaea werneckii, as well as to acidophilic fungi. One of the latter, able to grow at pH 0, is Scytalidium acidophilum, which is ascribed here to the newly validated genus Acidomyces. The ecological implications of this finding are discussed.

Development of natural culture media for rapid induction of Fonsecaea pedrosoi sclerotic cells in vitro

Fonsecaea pedrosoi is the main agent of chromoblastomycosis, a skin disease presenting verrucous lesions, in which round, thick-walled sclerotic cells are found. In vitro induction of sclerotic cells is time-consuming (20 to 45 days) and temperature dependent. We present two new natural media that reduce the sclerotic-cell induction time to only 2 days.

Biodiversity of the genus Cladophialophora

Cladophialophora is a genus of black yeast-like fungi comprising a number of clinically highly significant species in addition to environmental taxa. The genus has previously been characterized by branched chains of ellipsoidal to fusiform conidia. However, this character was shown to have evolved several times independently in the order Chaetothyriales. On the basis of a multigene phylogeny (nucLSU, nucSSU, RPB1), most of the species of Cladophialophora (including its generic type C. carrionii) belong to a monophyletic group comprising two main clades (carrionii- and bantiana-clades). The genus includes species causing chromoblastomycosis and other skin infections, as well as disseminated and cerebral infections, often in immunocompetent individuals. In the present study, multilocus phylogenetic analyses were combined to a morphological study to characterize phenetically similar Cladophialophora strains. Sequences of the ITS region, partial Translation Elongation Factor 1-alpha and beta-Tubulin genes were analysed for a set of 48 strains. Four novel species were discovered, originating from soft drinks, alkylbenzene-polluted soil, and infected patients. Membership of the both carrionii and bantiana clades might be indicative of potential virulence to humans.

Biology and pathogenesis of Fonsecaea pedrosoi, the major etiologic agent of chromoblastomycosis

Fonsecaea pedrosoi is the principal etiologic agent of chromoblastomycosis, a fungal disease whose pathogenic events are poorly understood. Treatment of the disease presents poor effectiveness and serious side effects. The disease is epidemiologically important in several regions, which has stimulated studies focused on the biology and pathogenic potential of its major causative agent. In this review, we summarize the current knowledge on the biological aspects of F. pedrosoi, including cell differentiation and pathogenic mechanisms during the interaction of fungi with different hosts' elements.

Molecular analysis and pathogenicity of the Cladophialophora carrionii complex, with the description of a novel species

Cladophialophora carrionii is one of the four major etiologic agents of human chromoblastomycosis in semi-arid climates. This species was studied using sequence data of the internal transcribed spacer region of rDNA, the partial beta-tubulin gene and an intron in the translation elongation factor 1-alpha gene, in addition to morphology. With all genes a clear bipartition was observed, which corresponded with minute differences in conidiophore morphology. A new species, C. yegresii, was introduced, which appeared to be, in contrast to C. carrionii, associated with living cactus plants. All strains from humans, and a few isolates from dead cactus debris, belonged to C. carrionii, for which a lectotype was designated. Artificial inoculation of cactus plants grown from seeds in the greenhouse showed that both fungi are able to persist in cactus tissue. When reaching the spines they produce cells that morphologically resemble the muriform cells known as the "invasive form" in chromoblastomycosis. The tested clinical strain of C. carrionii proved to be more virulent in cactus than the environmental strain of C. yegresii that originated from the same species of cactus, Stenocereus griseus. The muriform cell expressed in cactus spines can be regarded as the extremotolerant survival phase, and is likely to play an essential role in the natural life cycle of these organisms.

Effects of tricyclazole (5-methyl-1,2,4-triazol[3,4] benzothiazole), a specific DHN-melanin inhibitor, on the morphology of Fonsecaea pedrosoi conidia and sclerotic cells

The influence of tricyclazole (5-methyl-1,2,4-triazol[3,4]benzothiazole), a specific DHN-melanin inhibitor, on the cell walls and intracellular structures of Fonsecaea pedrosoi conidia and sclerotic cells was analyzed by transmission electron microscopy (TEM), deep-etching, and field emission scanning electron microscopy. The treatment of the fungus with 16 microg mL(-1) of tricyclazole (TC) did not significantly affect fungal viability, but electron microscopy observations showed several important morphological differences between TC-treated and non-TC treated cells. Control sclerotic cells presented patched granules, with an average diameter of 47 nm, on the cell surface, which were absent in TC-treated cells. Also, TC-treated sclerotic cells showed an undulated relief. TC treatment leads to an accumulation of electron lucent vacuoles in the fungal cytoplasm of both conidia and sclerotic cells, and treated conidia observed by deep etching showed a relevant thickening of the fungal cell wall. Together, these observations support the previous data of our group that F. pedrosoi synthesizes melanin in intracellular organelles. In addition, we suggest that melanin is not only an extracellular constituent but could also be dispersing all over the cell walls and could have an effective role in cross-linking different cell wall compounds that help maintain the regular shape of the cell wall.

The major chromoblastomycosis fungal pathogen, Fonsecaea pedrosoi, extracellularly releases proteolytic enzymes whose expression is modulated by culture medium composition: implications on the fungal development and cleavage of key's host structures

We investigated the possible secretion of peptidases by F. pedrosoi, when conidial cells were cultured in two distinct media. Aspartyl proteolytic activity was detected on the Czapeck-Dox-derived supernatant, which was blocked by pepstatin, and only active in extremely acidic conditions. The supernatant obtained after conidia growth in Kauffman medium presented metallopeptidase activity, which was active over a broad pH range and sensitive to 1,10-phenanthroline and EGTA. Additionally, both culture supernatants were able to cleave a wide range of proteinaceous substrates, including important human serum proteins (e.g. albumin and immunoglobulin G) and extracellular matrix components (e.g. fibronectin and laminin). As peptidases participate in different cellular metabolic pathways, we also tested the influence of proteolytic inhibitors on the F. pedrosoi conidia development in vitro. The metallopeptidase inhibitors, 1,10-phenanthroline, EGTA and EDTA, strongly abrogated the growth of conidial forms by approximately 95%, 85% and 60%, respectively. Moreover, 1,10-phenanthroline blocked the differentiation process from conidia to mycelia, an essential step during the F. pedrosoi life cycle. Phenylmethanesulfonyl fluoride, a serine peptidase inhibitor, slightly reduced the conidial growth, whereas proteolytic inhibitors of cysteine (E-64) and aspartic (pepstatin) type peptidases did not alter conidial developmental behavior. In summary, our results showed for the first time the expression of extracellular proteolytic activity by F. pedrosoi conidial cells.

Differentiation of Fonsecaea pedrosoi mycelial forms into sclerotic cells is induced by platelet-activating factor

Platelet-activating factor (PAF) has been shown to induce the differentiation of several cell types. In this work, we evaluated the effects of PAF on the formation of sclerotic cells of Fonsecaea pedrosoi, the major causative agent of chromoblastomycosis. Cell differentiation was evaluated by light and electron microscopy, which showed that treatment of mycelial forms with PAF results in the generation of sclerotic bodies with typical morphological characteristics. Biochemical features of PAF-induced sclerotic cells were also analyzed and compared with those from sclerotic forms induced by propranolol, a previously described differentiating agent of F. pedrosoi. Chemical analyses of lipid and carbohydrate components from PAF- or propranolol-induced sclerotic bodies revealed that palmitic, stearic, oleic and linoleic acids were the major fatty acid components, while glucose, mannose, galactose and rhamnose were detected as the principal sugar constituents in these cells. Surface carbohydrate components of PAF- and propranolol-induced sclerotic cells were also evaluated, by flow cytometry analysis with twelve different lectins. The profile of reactivity of PAF- or propranolol-induced fungal cells with lectins was also very similar. Hydrolysis of the synthetic substrate p-nitrophenylphosphate by fungal cells demonstrated that the addition of PAF or propranolol to the mycelial cultures similarly promotes a significant increase in ecto-phosphatase activity. These results indicate that the differentiation of F. pedrosoi mycelial cells induced by PAF generates authentic sclerotic forms, as confirmed by the analysis of morphological and biochemical attributes. Since PAF is synthesized in normal conditions by the human host, these observations may have a correlation with the differentiation of F. pedrosoi in vivo.

Molecular genetic studies of the model dematiaceous pathogen Wangiella dermatitidis

The rapidly improving molecular genetic tractability of Wangiella (Exophiala) dermatitidis significantly enhances its usefulness as a model for the more than 100 other dematiaceous (melanized) agents of human disease. Previously this model was based almost exclusively on its vegetative polymorphism, which at the simplest level is expressed as three well-characterized modes of growth (e.g., blastic, apical and isotropic) that produce myriad yeast, hyphal and sclerotic phenotypes. This cellular plasticity is important for a dematiaceous model pathogen because some are hyphal in nature but exist almost exclusively as sclerotic bodies in infected tissue, whereas others are hyphal both in nature and in tissue, and still others exist in nature predominantly as yeast, but as mixtures of yeast, hyphae and sclerotic bodies in tissue. By exploiting the polymorphism of W. dermatitidis, any phenotype of another dematiaceous pathogen can be produced for study of the regulation of its development and its contribution to pathogenicity and virulence. The coupling of this asset with the recent finding that its haploid, uninucleate yeast cell is easily transformed molecularly, and the even more recent development of systems for both random and targeted gene disruptions and for site-specific, integrative gene overexpression studies suggest that it will continue as the preferred model for the dematiaceous fungi and irrespective of the mycosis involved. The results reviewed here aim to confirm this contention, stimulate others to study this fungus, and demonstrate that W. dermatitidis is exceptionally useful for discovering by molecular genetic techniques cell wall-associated virulence factors in fungi, and in particular in the dematiaceous fungi.

Comparison of Fonsecaea pedrosoi sclerotic cells obtained in vivo and in vitro: ultrastructure and antigenicity

The parasitic form of Fonsecaea pedrosoi from the hyperkeratotic layer of the skin was obtained from four patients with chromoblastomycosis. Primary cultures containing hyphae and conidia were successfully converted into sclerotic cells in the presence of 800 microM propranolol and low pH as described before. The morphology of sclerotic cells of F. pedrosoi obtained in vivo and in vitro was analyzed by light and electron microscopy. Their antigenicity was also compared by immunofluorescence microscopy and ELISA assays, using serum samples from untreated patients infected with F. pedrosoi. Due to the similarity of the sclerotic cells obtained in vivo and in vitro, the latter can be more adequately in studies of host-parasite interactions in chromoblastomycosis.

Ca2+ fluxes in developing Trichoderma viride mycelium

The properties of both Ca2+ influx and efflux in the mycelium during the life cycle of Trichoderma viride were studied by means of 45Ca2+ and by X-ray fluorescence spectroscopy measurements. The properties of the 45Ca2+ influx and effluxes indicate that they are mediated by different transport systems. The Ca2+ influx could be mediated by an electrogenic Ca2+/nH+ antiport, or by an Ca2+ uniport system. Both Ca2+ influx and efflux were stimulated by the uncouplers (and the treatment leading to the suppression of energy metabolism) and by azalomycin F, an antifungal agent. Salicylate stimulated the Ca2+ efflux, but inhibited the Ca2+ influx. In the isolated preparation of crude vacuolar/mitochondrial fraction, salicylate induced the Ca2+ release, as did A23187. Azalomycin F moderately released Ca2+ from the microsomal fraction. On the other hand, uncouplers did not release Ca2+ from the isolated organelles, but inhibited to a different extent the ATP-dependent and -independent Ca2+ influx. The results could be explained in terms of the capacitative Ca2+ influx mechanism. The rate of 45Ca2+ influx, or of the 40Ca2+ content, was maximal after about 30 h of submerged cultivation, and then decreased. The results show that loading of internal Ca2+ stores occurs in the early stages of the development of mycelium only, and the Ca2+ influx mechanism is developmentally down-regulated, being almost nonexistent during its later stages. In older mycelium, growth seems to be autonomous of the extracellular Ca2+ until the onset of conidiation.

Significance of fungal evolution for the understanding of their pathogenicity, illustrated with agents of phaeohyphomycosis

Phaeohyphomycosis is an umbrella term for all those mycoses where the fungus is present in tissue with melanized filaments. It is surmised that some groups of species within the ascomycete family Herpotrichiellaceae exhibit an evolutionary tendency towards pathogenicity on vertebrate hosts. Such a tendency is not observed in the families Pleosporaceae and Dothideaceae. Mycoses provoked by members of the three families thus may be fundamentally different. Phaeohyphomycosis should be regarded as an artificial descriptor without biological significance.

Importance of calcium to the regulation of polymorphism in Wangiella (Exophiala) dermatitidis

Critical steps implicated in the polymorphism of Wangiella dermatitidis were found to be sensitive to calcium ion availability. When grown in a defined, synthetic medium under various pH and temperature conditions, two thresholds of calcium ion concentrations were identified: a lower concentration favouring non-polarized growth leading to multicellular form development and a higher concentration promoting polarized growth characterized by yeast budding or pseudo/true hyphal growth. The phenotypic transition of yeasts to multicellular forms or to hyphae was induced at both 25 and 37 degrees C in the wild-type strain by the addition of calcium to the synthetic medium adjusted to pH 2.5, which was otherwise not conducive to the production of either growth form. However, the calcium additions did not allow maintenance of polarized growth of yeasts or hyphae in a temperature-sensitive, cell-division-cycle mutant (wdcdc2) derived from the same strain and grown at 37 degrees C in the same medium adjusted to either pH 2.5 or 6.5. Instead these conditions allowed only the nonpolarized, multicellular form development associated with this conditional mutant cultured in rich media at the 37 degree C restrictive temperature for yeast bud formation. Results from experiments using the calcium chelator EGTA added to the synthetic medium supported these conclusions at neutral pH with both the wild type and the wdcdc2 mutant cultured at 37 degrees C. The results suggested that during infection different concentrations of calcium may be encountered by W. dermatitidis in different tissues, which might directly regulate its growth and polymorphism and indirectly its virulence depending on host conditions.

Stationary phase development of Trimmatostroma abietis

Processes of anamorph cell replication in Trimmatostroma abietis are described. Growth and conidiation are delimited on the basis of morphological, ultrastructural and ecological criteria. Cellular expansion shifts from bidirectional intercalary in exponential phase cells to isodiametric in late stationary phase cells, in the latter case with endogenous asexual reproduction. Ultrastructural similarities to dothideaceous black yeasts are discussed.

Identification of the conserved coding sequences of three chitin synthase genes in Fonsecaea pedrosoi

Primers having designs based on highly conserved stretches in the deduced amino acid sequences of chitin synthase (CHS) genes were used in PCR reactions to amplify 600 bp and 366 bp products from the genomic DNA of three major causal agents of chromoblastomycosis. Cloning and sequencing of the PCR products of one of these fungi, Fonsecaea pedrosoi, identified three CHS sequences designated as FpCHS1, FpCHS2 and FpCHS3. FpCHS1 and FpCHS2 were homologous to regions of CHS1 and CHS2 of Saccharomyces cerevisiae, and their derived amino acid sequences fell into chitin synthase classes I and II, respectively. FpCHS3 was homologous to a region of the CAL1/CSD2 gene of S. cerevisiae, which codes for the chitin synthase three (Chs3) enzyme in that fungus. Phylogenetic trees constructed using the deduced amino acid sequences of PCR-amplified CHS products from many fungi clustered F. pedrosoi with other dematiaceous fungi, providing new molecular evidence for the genetic relatedness of these organisms. The identification of these CHS genes in F. pedrosoi will facilitate future studies of the functional roles of chitin synthases in the unique in vivo dimorphism exhibited by chromoblastomycotic fungi.

Use of the polymerase chain reaction to identify coding sequences for chitin synthase isozymes in Phialophora verrucosa

Based on conserved amino-acid regions predicted for the chitin synthases (Chs) of Saccharomyces cerevisiae, two different primer sets were synthesized and used in polymerase chain reactions (PCRs) to amplify 614-bp and 366-bp sequences from genomic DNA of the zoopathogenic fungus Phialophora verrucosa. DNA-sequencing and Southern-blotting analyses of the 614-bp DNA amplification products suggested that portions of two distinct P. verrucosa chitin synthase genes (PvCHS1, PvCHS2), coding for two different zymogenic-type PvChs isozymes, had been identified. The deduced amino-acid sequence of each fell into different Chs classes, namely class I and class II. In addition, the 366-bp DNA segment was shown to code for a conserved region having homology with the CSD2/CAL1 gene of S. cerevisiae, which encodes a nonzymogenic-type enzyme, Chs3, in that fungus. The amino-acid sequence derived from PvCHS3 exhibits 88.2% similarity and 78.4% identity to the same amino-acid region of the S. cerevisiae enzyme. These results provide a critical first step toward investigating the molecular and pathogenic importance of CHS gene regulation in this fungus and for exploring steps leading to Chs function as potential targets for the design of new therapeutic agents.

Pleoanamorphic life cycle of Exophiala (Wangiella) dermatitidis

The anamorph life cycle of the black yeast Exophiala (Wangiella) dermatitidis is described. The fungus is dimorphic, yeast cells being the prevalent form of propagation. The fungus is strongly hydrophilic, probably completing its anamorph life cycle in submersion. Adaptation to dry conditions is slow. Types of conidiogenesis comprise annellidic, phialidic and sympodial reproduction, in addition to isotropic development. Phialoconidia fail to germinate under the conditions tested, and thus may have a function other than dispersal. Sterile, multicellular bodies resembling a Capronia teleomorph are described.