Cladosporium carrionii and Hormoconis resinae ( C. resinae ): Cell Wall and Melanin Studies

San-Blas, Gioconda; Guanipa, Omaira; Moreno, Belisario; Pékerar, Sara; San-Blas, Felipe

doi:10.1007/s002849900003

Cited by 34 publications

(25 citation statements)

References 24 publications

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“…Previous studies on F. pedrosoi suggested that melanin is partly deposited on the cell wall and mostly in cytoplasmic organelles resembling mammalian melanosomes (Alviano et al, 1991;Franzen et al, 1999). Similar membrane-enclosed structures have also been observed in other dematiaceous fungi such as C. carrioni and H. resinae (San-Blas et al, 1996). In the present work, the use of low viscosity Spurr embedding resin improved the visualization of the ultrastructure of the fungal melanosome by TEM.…”

Section: Discussionmentioning

confidence: 50%

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Ultrastructural characterization of melanosomes of the human pathogenic fungus Fonsecaea pedrosoi

Franzen

Cunha

Miranda³

et al. 2008

Journal of Structural Biology

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Section: Discussionmentioning

confidence: 50%

“…However, Alviano et al (1991) showed that in the black fungi Fonsecaea pedrosoi, melanin is synthesized within membrane bounded structures referred to as melanosomes. Similar organelles were described in other black fungi, such as Cladosporium carrioni and Hormoconis resinae (San-Blas et al, 1996).…”

Section: Introductionmentioning

confidence: 77%

Ultrastructural characterization of melanosomes of the human pathogenic fungus Fonsecaea pedrosoi

Franzen

Cunha

Miranda³

et al. 2008

Journal of Structural Biology

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“…In none of the electron micrographs ( Fig. 2 to 6) were the C. albicans melanosomes obviously enclosed in membranes, unlike some other illustrations of fungal melanosomes (2,26,73), but the size and form of the dark granules was otherwise consistent with the interpretation that they were indeed melanosomes.…”

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confidence: 61%

“…However, vesicles externalized from C. neoformans cells also show laccase activity (21), so the effect of chitin may be on vesicle externalization rather than on melanin itself. Internal structures compatible with mammalian melanosomes have been observed in Cladosporium carrionii (73) and in Fonsecaea pedrosoi (2,26). Remarkably, F. pedrosoi also secretes melanin and locates the polymer within the cell wall (1,2,25,27,74).…”

mentioning

confidence: 79%

“…We interpret these structures to be melanosomes that had been transported to the cell exterior, where they remained attached to the cell wall. While melanosomes in human melanocytes typically show a delimiting membrane by electron microscopy (76), a similarly self-evident bounding membrane is noted only for a minority of fungal melanosomes (2,27,73). When TEM sections were prepared without exposure to osmium and uranium salts, the externalized melanosomes remained electron dense and were seen clearly in cultures of C. albicans grown in the presence of DOPA (Fig.…”

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confidence: 99%

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Melanin Externalization in Candida albicans Depends on Cell Wall Chitin Structures

et al. 2010

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The fungal pathogen Candida albicans produces dark-pigmented melanin after 3 to 4 days of incubation in medium containing L-3,4-dihydroxyphenylalanine (L-DOPA) as a substrate. Expression profiling of C. albicans revealed very few genes significantly up-or downregulated by growth in L-DOPA. We were unable to determine a possible role for melanin in the virulence of C. albicans. However, we showed that melanin was externalized from the fungal cells in the form of electron-dense melanosomes that were free or often loosely bound to the cell wall exterior. Melanin production was boosted by the addition of N-acetylglucosamine to the medium, indicating a possible association between melanin production and chitin synthesis. Melanin externalization was blocked in a mutant specifically disrupted in the chitin synthase-encoding gene CHS2. Melanosomes remained within the outermost cell wall layers in chs3⌬ and chs2⌬ chs3⌬ mutants but were fully externalized in chs8⌬ and chs2⌬ chs8⌬ mutants. All the CHS mutants synthesized dark pigment at equivalent rates from mixed membrane fractions in vitro, suggesting it was the form of chitin structure produced by the enzymes, not the enzymes themselves, that was involved in the melanin externalization process. Mutants with single and double disruptions of the chitinase genes CHT2 and CHT3 and the chitin pathway regulator ECM33 also showed impaired melanin externalization. We hypothesize that the chitin product of Chs3 forms a scaffold essential for normal externalization of melanosomes, while the Chs8 chitin product, probably produced in cell walls in greater quantity in the absence of CHS2, impedes externalization.Candida albicans is a major opportunistic fungal human pathogen that causes a wide variety of infections (9, 68). In healthy individuals C. albicans resides as a commensal within the oral cavity and gastrointestinal and urogenital tracts. However, in immunocompromised hosts, C. albicans causes infections ranging in severity from mucocutaneous infections to life-threatening disseminated diseases (9, 68). Research into the pathogenicity of C. albicans has revealed a complex mix of putative virulence factors (7, 60), perhaps reflecting the fine balance this species strikes between commensal colonization and opportunistic invasion of the human host.Melanins are biological pigments, typically dark brown or black, formed by the oxidative polymerization of phenolic compounds. They are negatively charged hydrophobic molecules with high molecular weights and are insoluble in both aqueous and organic solvents. Their insolubility makes melanins difficult to study, and no definitive structure has yet been found for them; they probably represent an amorphous mixture of polymers (35). There are various types of melanin in nature, including eumelanin and phaeomelanin (76). Two principal types of melanin are found in the fungal kingdom. The majority are 1.8-dihydroxynapthalene (DNH) melanins synthesized from acetyl-coenzyme A (CoA) via the polyketide pathway (5). DNH melanins have been foun...

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Production of melanin pigments in saprophytic fungi in vitro and during infection

et al. 2019

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Melanins are one of the great natural pigments produced by a wide variety of fungal species that promote fitness and cell survival in diverse hostile environments, including during mammalian infection. In this study, we sought to demonstrate the production of melanin in the conidia and hyphae of saprophytic fungi, including dematiaceous and hyaline fungi. We showed that a melanin‐specific monoclonal antibody (MAb) avidly labeled the cell walls of hyphae and conidia, consistent with the presence of melanin in these structures, in 14 diverse fungal species. The conidia of saprophytic fungi were treated with proteolytic enzymes, denaturant, and concentrated hot acid to yield dark particles, which were shown to be stable free radicals, consistent with their identification as melanins. Samples obtained from patients with fungal keratitis due to Fusarium falciforme, Aspergillus fumigatus, Aspergillus flavus, Curvularia lunata, Exserohilum rostratum, or Fonsecaea pedrosoi were found to be intensely labeled by the melanin‐specific MAb at the fungal hyphal cell walls. These results support the hypothesis that melanin is a common component that promotes survival under harsh conditions and facilitates fungal virulence. Increased understanding of the processes of melanization and the development of methods to interfere with pigment formation may lead to novel approaches to combat these complex pathogens that are associated with high rates of morbidity and mortality.

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Cladosporium carrionii and Hormoconis resinae ( C. resinae ): Cell Wall and Melanin Studies

Cited by 34 publications

References 24 publications

Ultrastructural characterization of melanosomes of the human pathogenic fungus Fonsecaea pedrosoi

Ultrastructural characterization of melanosomes of the human pathogenic fungus Fonsecaea pedrosoi

Melanin Externalization in Candida albicans Depends on Cell Wall Chitin Structures

Production of melanin pigments in saprophytic fungi in vitro and during infection

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