Abstract
Melanins are synthesized by organisms of all biological kingdoms and comprise a heterogeneous class of natural pigments. Certain of these polymers have been implicated in the pathogenesis of several important human fungal pathogens. This study investigated whether the fungal skin pathogen Malassezia furfur produces melanin or melanin-like compounds. A melanin-binding monoclonal antibody (MAb) labelled in vitro cultivated yeast cells of M. furfur. In addition, melanization of Malassezia yeasts and hyphae was detected by anti-melanin MAb in scrapings from patients with pityriasis versicolor. Treatment of Malassezia yeasts with proteolytic enzymes, denaturant and concentrated hot acid yielded dark particles and electron spin resonance spectroscopy revealed that these particles contained a stable free radical compound, consistent with their identification as melanins. Malassezia yeasts required phenolic compounds, such as L-DOPA, in order to synthesize melanin. L-DOPA also triggered hyphal formation in vitro when combined with kojic acid, a tyrosinase inhibitor, in a dose-dependent manner. In this respect, L-DOPA is thought to be an essential substance that is linked to both melanization and yeast-mycelial transformation in M. furfur. In summary, M. furfur can produce melanin or melanin-like compounds in vitro and in vivo, and the DOPA melanin pathway is involved in cell wall melanization.
Highlights
Malassezia species are lipophilic yeasts that are frequent components of the skin microflora of humans and most warmblooded animals [1], [2]
Pityriasis versicolor (PV), known as tinea versicolor, is a common superficial skin infection restricted to the stratum corneum that occurs when Malassezia yeast cells convert to a pathogenic mycelial form
M. furfur yeast cells grown in minimal medium without LDOPA were macroscopically non-pigmented (Figure 1B), and the non-pigmented cells were completely solubilized by subjecting them to the melanin extraction protocol
Summary
Malassezia species are lipophilic yeasts that are frequent components of the skin microflora of humans and most warmblooded animals [1], [2]. Based on molecular data and lipid requirements, seven Malassezia species are recognized [3], [4]. Pityriasis versicolor (PV), known as tinea versicolor, is a common superficial skin infection restricted to the stratum corneum that occurs when Malassezia yeast cells convert to a pathogenic mycelial form. M. globosa and M. furfur are significantly more common causes of PV than other species [5]. The disease is characterized by the presence of fine scaly patches or macules, which may be either hypo- or hyperpigmented, that are normally located on the upper parts of trunk, neck, and arms [5], [6]. PV is one of the most common pigmentary disorders worldwide, but it is more common in tropical climates, reaching as high as 50% in some tropical areas, which is attributed to the growth benefit achieved in the relative high temperature and humidity of these regions [5]
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