Abstract
The fungal pathogen Penicillium marneffei produces melanin-like pigment in vitro. The synthetic pathway of melanin and its possible influence in the protective yeast cells surviving within macrophage cells are not known. In this work, P. marneffei produced brown black pigment in the presence of L-DOPA and black particles were extracted from yeast cells treated with proteolytic enzymes, denaturant and concentrated hot acid. Kojic acid inhibited the brown-black pigment production of P. marneffei yeast grown on brain heart infusion agar. Transmitting electron microscopy showed spherical granular electron-dense particles with an average diameter of 100 nm in a beaded arrangement in the innermost cell wall. Electron-paramagnetic resonance revealed that the black particles contain a stable free radical compound. The UV-visible and Fourier transform infrared spectra of particles extracted from P. marneffei and synthetic DOPA-melanin showed a high degree of similarity. Melanized yeast cells decreased phagocytosis by macrophage cells and increased resistance to intracellular digestion in vitro. These results indicate that P. marneffei can synthesize DOPA-melanin or melanin-like compounds in vitro and suggest that the DOPA-melanin pathway is associated with cell wall structure and enhances the resistance to phagocytosis by macrophages.
Highlights
Penicillium marneffei, recently renamed as Talaromyces marneffei [1], is a thermally dimorphic fungus that appears in mycelia form at 25uC and yeast form at 37uC
The yeast cells of P. marneffei isolated from the chemically defined medium with L-DOPA appeared as dark brown (Fig. 1B) and darkly pigmented particles was isolated from the yeast cells (Fig. 1C)
We found that P. marneffei can synthesize DOPA-melanin or melanin-like compounds in vitro
Summary
Penicillium marneffei, recently renamed as Talaromyces marneffei [1], is a thermally dimorphic fungus that appears in mycelia form at 25uC and yeast form at 37uC. The fungus is endemic in Southeast Asia and causes systemic infection in humans, especially in immune suppressed individuals. P. marneffei infection is fatal if untreated in immunocompromised hosts. The pathogen has become one of the most common HIV-related infections in Southeast Asia [2,3]. The ability of P. marneffei yeast cells to survive within host cells is essential to enable the fungus to produce systemic infection, and this survival ability renders the fungus difficult to be completely cleared from the body. The mechanisms by which P. marneffei protects itself from the host immune defense remain unclear. Expression of acid phosphatase activity in P. marneffei yeast cells [4], and the upregulation of the cpeA and sodA genes in this yeast phase [5,6], may be associated with the oxidative stress response during intracellular infection
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