L-tyrosine induces the production of a pyomelanin-like pigment by the parasitic yeast-form of Histoplasma capsulatum

Abstract

Melanization of Histoplasma capsulatum remains poorly described, particularly in regards to the forms of melanin produced. In the present study, 30 clinical and environmental H. capsulatum strains were grown in culture media with or without L-tyrosine under conditions that produced either mycelial or yeast forms. Mycelial cultures were not melanized under the studied conditions. However, all strains cultivated under yeast conditions produced a brownish to black soluble pigment compatible with pyomelanin when grew in presence of L-tyrosine. Sulcotrione inhibited pigment production in yeast cultures, strengthening the hyphothesis that H. capsulatum yeast forms produce pyomelanin. Since pyomelanin is produced by the fungal parasitic form, this pigment may be involved in H. capsulatum virulence.

Figure 1.

Pyomelanin production by H. capsulatum: (A) strain IPEC22/11 (1 × 10³ cells/ml) inoculated in MM added with L-tyrosine at 30 °C, (B) production of a soluble melanoid pigment by this same strain when the yeast form of the fungus was incubated at 37 °C in HAM’s F12 medium supplemented with L-tyrosine, (C) EPR spectrum from supernatants of H. capsulatum cultures under different conditions. This Figure is reproduced in color in the online version of Medical Mycology.