Cell-surface hydrophobicity and lipolysis as essential factors in human tinea nigra

Decoding arthropod vector immunology through bona fide pathogens

The interrelationship between the microbiota, metabolism, and the arthropod immune system has evolved to maintain physiological equilibrium. Arthropods rely on this delicate balance when encountering fitness challenges. The understanding of life history traits in arthropod vectors has been hampered by technological difficulties compounded by limited scientific knowledge compared to established model organisms. Here, we posit that using emerging technologies to study environmental pathogens that cause greater fitness disadvantages to disease vectors (i.e., bona fide pathogens) in contrast to coevolved microbes will enable meaningful insights into arthropod immunophysiology. We propose a conceptual framework whereby understanding immunophysiology through the lens of bona fide pathogens, as opposed to coevolved microbes, should be useful for the management of vector-borne illnesses.

Assessing pH-dependent activities of virulence factors secreted by Candida albicans

Candida albicans is an opportunistic pathogen that can thrive under adverse conditions including suboptimal pH, nutrient scarcity, and low levels of oxygen. Its pathogenicity is associated with the production of virulence factors such as extracellular hydrolytic enzymes and toxins. This study was aimed at determining the effect of external pH, substrate nature, and strain origin on protease, lipase, and hemolysin production. To achieve this objective, agar plate assays were performed at pH 5.0, 6.5, and 7.5 with substrates suitable for the detection of each family of enzymes. Moreover, the study was conducted with 20 clinical C. albicans isolates from blood, oral cavity, skin, urine, and vagina. The hydrolytic zones formed around the colonies were further measured to calculate the Ez (enzymatic zone) indexes. We found that detection of proteases in skim milk agar plates was possible for most isolates only at pH 5 (80%) and pH 6.5 (75%), whereas BSA plates could confer protease detection exclusively at pH 5 (80%). Similarly, the percentage of isolates possessing lipolytic activities was higher at pH 5 (90%) than at pH 6.5 (70%) and pH 7.5 (35%). In contrast, hemolytic activities were detected in all isolates at pH 6.5 and 7.5 but not at pH 5. Further analysis revealed that some differences in the detected activities could potentially be attributed to the anatomical origin of these isolates. Collectively, these findings suggest that the pH of the site of infection might be critical for mimicking the microenvironment employed to experimentally discover the key virulence factors.

Divergent substrate specificities and regioselectivities of three lipase isoforms from Cordyceps militaris: Combinatorial advantages for entomopathogenicity and prospects as biocatalysts

Cordyceps militaris, an entomopathogenic Cordyceps mushroom, is a crucial ethnopharmacological agricultural product with applications in traditional oriental remedies in East Asia. Since lipases are reported to serve as key enzymatic equipment for entomopathogenic fungi during the host infection, the presence of various lipases with different biochemical features in C. militaris was elucidated. Three lipases from C. militaris (CML) of 60-70 kDa were isolated according to protein hydrophobicity; isoform relationships were identified by peptide mapping using liquid chromatography-electrospray ionization-tandem mass spectrometry. The CML isoforms exhibited distinct substrate specificities, which were related to the hydrophobicity of each isoform. Furthermore, the integral stereoselectivity of each lipase towards trioleoylglycerol diverged into two classes (sn-1,3 and sn-2 regioselectivity) that are rare in canonical fungal lipases. Overall, our results demonstrate that C. militaris secretes lipase isoforms with cocktail-like enzyme functions that may contribute to the entomopathogenic life cycle of C. militaris. Each CML isoform has distinct advantages for biocatalyst applications in the food and oleochemical industries.

Whole Genome Sequencing and Comparative Genome Analysis of the Halotolerant Deep Sea Black Yeast Hortaea werneckii

Hortaea werneckii, an extreme halotolerant black yeast in the order of Capnodiales, was recently isolated from different stations and depths in the Mediterranean Sea, where it was shown to be the dominant fungal species. In order to explore the genome characteristics of these Mediterranean isolates, we carried out a de-novo sequencing of the genome of one strain isolated at a depth of 3400 m (MC873) and a re-sequencing of one strain taken from a depth of 2500 m (MC848), whose genome was previously sequenced but was highly fragmented. A comparative phylogenomic analysis with other published H. werneckii genomes was also carried out to investigate the evolution of the strains from the deep sea in this environment. A high level of genome completeness was obtained for both genomes, for which genome duplication and an extensive level of heterozygosity (~4.6%) were observed, supporting the recent hypothesis that a genome duplication caused by intraspecific hybridization occurred in most H. werneckii strains. Phylogenetic analyses showed environmental and/or geographical specificity, suggesting a possible evolutionary adaptation of marine H. werneckii strains to the deep sea environment. We release high-quality genome assemblies from marine H. werneckii strains, which provides additional data for further genomics analysis, including niche adaptation, fitness and evolution studies.

The beauty and the yeast: can the microalgae Dunaliella form a borderline lichen with Hortaea werneckii?

Lichenized fungi usually develop complex, stratified morphologies through an intricately balanced living together with their algal partners, but several species are known to form only more or less loose associations with algae. These borderline lichens are still little explored although they could inform us about early stages of lichen evolution. We studied the association of the extremely halotolerant fungus Hortaea werneckii with the alga Dunaliella atacamensis, discovered in a cave in the Atacama Desert (Chile), and with D. salina, common inhabitant of saltern brines. D. atacamensis forms small colonies, in which cells of H. werneckii can be frequently observed, while such interaction has not been observed with D. salina. As symbiotic interactions between Dunaliella and Hortaea have not been reported, we performed a series of co-cultivation experiments to inspect whether these species could interact and develop more distinct lichen-like symbiotic structures. We set up co-cultures between axenic strains of Hortaea werneckii (isolated both from Mediterranean salterns and from the Atacama cave) and isolates of D. atacamensis (from the Atacama cave) and D. salina (isolated from Mediterranean salterns). Although we used different growth media and cultivation approaches, bright field and SEM microscopy analyses did not indicate any mutual effects in these experiments. We discuss the implications for fungal algal interactions along the transition from algal exploiters to lichen symbioses.

Global Molecular Diversity of the Halotolerant Fungus Hortaea werneckii

A global set of clinical and environmental strains of the halotolerant black yeast-like fungus Hortaea werneckii are analyzed by multilocus sequencing and AFLP, and physiological parameters are determined. Partial translation elongation factor 1-α proves to be suitable for typing because of the presence/absence of introns and also the presence of several SNPs. Local clonal expansion could be established by a combination of molecular methods, while the population from the Mediterranean Sea water also responds differently to combined temperature and salt stress. The species comprises molecular populations, which in part also differ physiologically allowing further diversification, but clinical strains did not deviate significantly from their environmental counterparts.

The HOG signal transduction pathway in the halophilic fungus Wallemia ichthyophaga: identification and characterisation of MAP kinases WiHog1A and WiHog1B

The high-osmolarity glycerol (HOG) pathway is one of the several MAP kinase cascades in fungi. It is the main signal transduction system that is responsible for cellular stress responses, and has primarily been studied in the context of osmotic stress. In the present study, we provide the first insights into the HOG pathway of the obligatory halophilic basidiomycetous fungus Wallemia ichthyophaga, with the characterisation of its two Hog1-like kinases: WiHog1A and WiHog1B. These share high similarity to Hog1 kinase from Saccharomyces cerevisiae (ScHog1) at the level of amino-acid sequence. While WiHog1A could not optimally complement the function of ScHog1, WiHog1B was a fully functional Hog1-like kinase and could improve the halotolerance of the yeast, compared to the wild-type or the ScHog1-expressing hog1Δ strain. In W. ichthyophaga cells, Hog1 was constitutively phosphorylated under optimal osmotic conditions and dephosphorylated when the cells were challenged with hypo-osmolar or hyperosmolar stress. This pattern of phosphorylation kinetics is opposite to that of yeast. Transcriptional analysis of these two kinases in W. ichthyophaga shows that WiHOG1B is more responsive to changes in NaCl concentrations than WiHOG1A. Our identification and characterisation of these Hog1-like kinases from W. ichthyophaga confirm the existence of the HOG signalling pathway and its role in osmosensing in this halophilic fungus.

Tinea nigra by Hortaea werneckii, a report of 22 cases from Mexico

Tinea nigra is a superficial mycosis caused by Hortaea werneckii. It is an infrequent asymptomatic infection that affects human palms and soles, and is mostly observed in tropical countries. We evaluate retrospectively twenty-two confirmed cases of tinea nigra from a total of eleven yr (1997–2007) and discuss the epidemiology, clinical features and treatment of this disease. In twelve cases, adults were involved, in 10, children. In nineteen cases the disorder was located on palms of hands and in three on soles of feet. In all cases, the obtained isolates were morphologically identified as Hortaea werneckii and the identification of ten isolates was retrospectively confirmed with the help of sequences of the internal transcribed spacer regions of the ribosomal DNA. The patients received topical treatment with Whitfield ointment, ketoconazole, bifonazole, or terbinafine. Treatment with keratolytic agents and topical antifungals was effective.

Selective factors involved in oil flotation isolation of black yeasts from the environment

The oil flotation isolation technique has been successfully applied to recover chaetothyrialean black yeasts and relatives from the environment. The selective mechanisms playing a role in isolation are unknown. The fungi concerned are supposed to occupy specialized microniches in nature, taking advantage of (1) oligotrophism. Mineral oil as a main selective agent may be based on (2) hydrophobicity or on (3) assimilation. All three hypotheses are tested in this paper. Results show that cell wall hydrophobicity is unlikely to be a selective factor. Incubation under poor nutrient conditions provides competitive advantage for black yeasts, especially for Exophiala strains, which are subsequently enriched by mineral oil which enhances growth in this group of fungi. Incubation under mineral media and mineral oil can be used as selective factor.

Adaptation of extremely halotolerant black yeast Hortaea werneckii to increased osmolarity: a molecular perspective at a glance

Halophilic adaptations have been studied almost exclusively on prokaryotic microorganisms. Discovery of the black yeast Hortaea werneckii as the dominant fungal species in hypersaline waters enabled the introduction of a new model organism to study the mechanisms of salt tolerance in eukaryotes. Its strategies of cellular osmotic adaptations on the physiological and molecular level revealed novel, intricate mechanisms to combat fluctuating salinity. H. werneckii is an extremely halotolerant eukaryotic microorganism and thus a promising source of transgenes for osmotolerance improvement of industrially important yeasts, as well as in crops.

Fungal adaptation to extremely high salt concentrations

Hypersaline environments support substantial microbial communities of selected halotolerant and halophilic organisms, including fungi from various orders. In hypersaline water of solar salterns, the black yeast Hortaea werneckii is by far the most successful fungal representative. It has an outstanding ability to overcome the turgor loss and sodium toxicity that are typical for hypersaline environments, which facilitates its growth even in solutions that are almost saturated with NaCl. We propose a model of cellular responses to high salt concentrations that integrates the current knowledge of H. werneckii adaptations. The negative impact of a hyperosmolar environment is counteracted by an increase in the energy supply that is needed to drive the energy-demanding export of ions and synthesis of compatible solutes. Changes in membrane lipid composition and cell-wall structure maintain the integrity and functioning of the stressed cells. Understanding the salt responses of H. werneckii and other fungi (e.g., the halophilic Wallemia ichthyophaga) will extend our knowledge of fungal stress tolerance and promote the use of the currently unexploited biotechnological potential of fungi that live in hypersaline environments.

Candida parapsilosis, an emerging fungal pathogen

SUMMARY

Candida parapsilosis is an emerging major human pathogen that has dramatically increased in significance and prevalence over the past 2 decades, such that C. parapsilosis is now one of the leading causes of invasive candidal disease. Individuals at the highest risk for severe infection include neonates and patients in intensive care units. C. parapsilosis infections are especially associated with hyperalimentation solutions, prosthetic devices, and indwelling catheters, as well as the nosocomial spread of disease through the hands of health care workers. Factors involved in disease pathogenesis include the secretion of hydrolytic enzymes, adhesion to prosthetics, and biofilm formation. New molecular genetic tools are providing additional and much-needed information regarding C. parapsilosis virulence. The emerging information will provide a deeper understanding of C. parapsilosis pathogenesis and facilitate the development of new therapeutic approaches for treating C. parapsilosis infections.

The sterile microfilamentous lichenized fungi Cystocoleus ebeneus and Racodium rupestre are relatives of plant pathogens and clinically important dothidealean fungi

The phylogenetic positions of the always-sterile microfilamentous lichens Cystocoleus ebeneus and Racodium rupestre were studied in a phylogenetic framework using sequence data of 5' nuSSU, nuLSU, and mtSSU rDNA. The analysis reveals that both genera are ascomycetes and belong to Dothideomycetidae: they are not close to lichenized members within the subclass, but rather belong to Capnodiales. The macroscopically scarcely distinguishable C. ebeneus and R. rupestre do not form a monophyletic group. The well-supported clade of R. rupestre is basal to the one in which C. ebeneus is close to Mycosphaerellaceae. This study provides another example of ascomycetes with very different life-styles and ecologies being closely related.

Role of lipase in Burkholderia cepacia complex (Bcc) invasion of lung epithelial cells

The Burkholderia cepacia complex (Bcc) is a group of ten closely related species associated with life-threatening infection in cystic fibrosis (CF). These bacteria are highly antibiotic resistant, with some strains transmissible, and in a subgroup of patients, they can cause a rapid and fatal necrotising pneumonia. The Bcc organisms produce a range of exoproducts with virulence potential, including exopolysaccharide, proteases and lipases. Many members of the Bcc are also capable of epithelial cell invasion, although the mechanism(s) involved are poorly understood. This study investigates a role for Bcc lipase in epithelial cell invasion by Bcc strains. Lipase activity was measured in eight species of the Bcc. Strains that produced high levels of lipase were predominantly from the B. multivorans and B. cenocepacia species. Pre-treatment of two epithelial cell lines with Bcc lipase significantly increased invasion by two B. multivorans strains and one B. cenocepacia strain and did not affect either plasma membrane or tight junction integrity. Inhibition of Bcc lipase production by the lipase inhibitor Orlistat significantly decreased invasion by both B. multivorans and B. cenocepacia strains in a concentration-dependent manner. This study demonstrates the extent of lipase production across the Bcc and establishes a potential role for lipase in Bcc epithelial cell invasion.

Lipase 8 affects the pathogenesis of Candida albicans

The production of lipases can affect microbial fitness and virulence. We examined the role of the lipase 8 (LIP8) gene in the virulence of Candida albicans by constructing Deltalip8 strains by the URA-blaster disruption method. Reverse transcription-PCR experiments demonstrated the absence of LIP8 expression in the homozygous knockout mutants. Reconstituted strains and overexpression mutants were generated by introducing a LIP8 open reading frame under control of a constitutive actin promoter. Knockout mutants produced more mycelium, particularly at higher temperatures and pH >or=7. Diminished LIP8 expression resulted in reduced growth in lipid-containing media. Mutants deficient in the LIP8 gene were significantly less virulent in a murine intravenous infection model. The results clearly indicate that Lip8p is an important virulence factor of C. albicans.

DNA array analysis ofCandida albicansgene expression in response to adherence to polystyrene

Candidiasis is often initiated by the colonization of inert surfaces. In order to elucidate the mechanisms involved in this adherence process, DNA macroarrays were used to analyze the transcriptome of Candida albicans, the main causative agent of this mycoses, in a simple adherence model using germ tubes produced in polystyrene Petri dishes. Non-adherent germ tubes produced on glass surface were used as a control. Analysis of gene expression displayed 77 genes identified as statistically overexpressed in adherent germ tubes. Among these genes, some encoded enzymes participating in metabolism of lipids (such as LIP6), of proteins (such as SAP1) or of carbohydrates (like PGI1, PMI40 and PSA1. Some of these genes have already been reported as playing a role in pathogenesis of C. albicans. However, functions were unknown for a large part (45.5%) of the overexpressed genes which will be analyzed further in order to define their relationship with adherence.

Lipid-induced filamentous growth in Ustilago maydis

The phytopathogenic fungus Ustilago maydis is obligately dependent on infection of maize to complete the sexual phase of its life cycle. Mating interactions between haploid, budding cells establish an infectious filamentous cell type that invades the host, induces large tumours and eventually forms large masses of black spores. The ability to switch from budding to filamentous growth is therefore critical for infection and completion of the life cycle, although the signals that influence the transition have not been identified from the host or the environment. We have found that growth in the presence of lipids promotes a filamentous phenotype that resembles the infectious cell type found in planta. In addition, the ability of the fungus to respond to lipids is dependent on both the cAMP signalling pathway and a Ras/MAPK pathway; these pathways are known to regulate mating, filamentous growth and pathogenesis in U. maydis. Overall, these results lead us to hypothesize that lipids may represent one of the signals that promote and maintain the filamentous growth of the fungus in the host environment.

Estudo de nove casos de tinha negra observados na Grande Vitória (Espírito Santo, Brasil) durante período de cinco anos

FUNDAMENTOS: Tinha negra ou ceratofitose negra constitui-se em infecção fúngica crônica do estrato córneo da epiderme, rara, causada pelo fungo filamentoso Phaeoannellomyces werneckii. Caracteriza-se clinicamente por mancha acastanhada, de limites nítidos, pouco descamativa, assintomática, preferencialmente localizada na palma da mão. OBJETIVO: Registrar a presença de casos de tinha negra no Estado do Espírito Santo e descrever suas características epidemiológicas. CASUÍSTICA E MÉTODOS: Foram pesquisados casos com o diagnóstico clínico de tinha negra em meio a todos os pacientes submetidos a exames laboratoriais para a determinação de fungos no laboratório do Serviço de Dermatologia de Vitória, no período de primeiro de janeiro de 1998 a primeiro de janeiro de 2003. RESULTADOS: Foram encontrados nove casos de tinha negra, sendo todos os portadores da raça branca com lesão localizada em uma das palmas das mãos; sete casos (77,7%) no sexo feminino, e seis casos (66,6%) na faixa de idade pré-escolar. Houve confirmação laboratorial em todos os casos. CONCLUSÕES: a) Foram diagnosticados nove casos de tinha negra durante o estudo, mesmo em região de praia; b) o sexo feminino, a raça branca e as crianças foram mais freqüentemente acometidos; c) a localização preferencial foi na região palmar, com predileção pela mão esquerda.

Expression analysis of the Candida albicans lipase gene family during experimental infections and in patient samples

Secreted lipases of Candida albicans are encoded by a gene family with at least 10 members (LIP1-LIP10). The expression pattern of this multigene family was investigated using reverse transcription polymerase chain reaction in experimental infections and in samples of patients suffering from oral candidosis. The findings illustrate that individual lipase genes are differentially regulated in a mouse model of systemic candidosis with some members showing sustained expression and others being transiently expressed or even silent. The lipase gene expression profile depended on the stage of infection rather than on the organ localization. This temporal regulation of lipase gene expression was also detected in an experimental model of oral candidosis. Furthermore, the expression of candidal lipase genes in human specimens is shown for the first time.

Tinea corporis, tinea cruris, tinea nigra, and piedra

Tinea infections are among the most common dermatologic conditions throughout the world. To avoid a misdiagnosis, identification of dermatophyte infections requires both a fungal culture on Sabouraud's agar media, and a light microscopic mycologic examination from skin scrapings. Topical antifungals may be sufficient for treatment of tinea corporis and cruris and tinea nigra, and the shaving of hair infected by piedra may also be beneficial. Systemic therapy, however, may be required when the infected areas are large, macerated with a secondary infection, or in immunocompromised individuals. Preventative measures of tinea infections include practicing good personal hygiene; keeping the skin dry and cool at all times; and avoiding sharing towels, clothing, or hair accessories with infected individuals.

Analyses of phagocytosis, evoked oxidative burst, and killing of black yeasts by human neutrophils: a tool for estimating their pathogenicity?

The pathogenicity of several dematiaceous yeasts that have, to date, rarely been isolated in humans remains unclear. Because professional phagocytes are prominent in lesions caused by dematiaceous fungi, we address this issue by comparing phagocytosis, evoked oxidative burst and killing by human neutrophils of different black yeasts in vitro. Whereas phagocytosis of all black yeasts tested and evoked oxidative burst yielded comparable results, in contrast, the degree of killing differed significantly after 5 h. Thereby, two groups could be identified; one in which strains are killed at high rates, for example, Hortaea werneckii (81 +/- 11.6%), Exophiala castellanii (96 +/- 8.6%), Phaeoannellomyces elegans (93 +/- 9.7%), Phaeococcomyces exophialae (87 +/- 8.7%), and the other in which strains are killed to a lesser degree, for example, Exophiala dermatitidis (ATCC 34100) (61 +/- 9.5%), E. dermatitidis (CBS 207.35) (66 +/- 7.5%), E. jeanselmei (50 +/- 10.5%), E. mesophila (63 +/- 11.6%), E. bergeri (63 +/- 9.1%), and E. spinifera (57 +/- 9.6%). Non-pigmented yeasts were killed at levels comparable with those at which the white mutant strain of E. dermatitidis (ATCC 44504) was killed (95 +/- 7.5%); the yeast strains tested were Candida albicans (DSM 11943) (95 +/- 4.0% killing) and Saccharomyces cerevisiae (DSM 1333) (95 +/- 10.3%). Comparison of killing rates with the observed pathogenicity of the melanized species suggests that low killing rates might indicate or even predict a high degree of invasiveness. Although previous experiments revealed that melanization conferred killing resistance on E. dermatitidis, the differences in killing rates of other dematious fungi suggest that melanization of the cell wall is in itself insufficient to confer virulence.

Onychomycosis caused by Blastoschizomyces capitatus

Blastoschizomyces capitatus was cultured from the nail of a healthy patient with onychomycosis. The identity of the isolate was initially established by standard methods and ultrastructural analysis and was verified by molecular probing. Strains ATCC 200929, ATCC 62963, and ATCC 62964 served as reference strains for these analyses. To our knowledge, this is the first case of nail infection secondary to paronychia caused by this organism reported in the English literature.

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.