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Infection and Immunity, June 2000, p. 3696-3703, Vol. 68, No. 6
0019-9567/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

Biosynthesis and Functions of Melanin in Sporothrix schenckii

Rafael Romero-Martinez,1 Michael Wheeler,2 Antonieta Guerrero-Plata,1 Guadalupe Rico,3 and Haydée Torres-Guerrero1,*

Departamento de Microbiología y Parasitología, Facultad de Medicina, UNAM, CP 04510, Mexico City D.F. 04510,1 and Unidad de Investigacion en Inmunologia, Hospital de Pediatria, CMN-IMSS Siglo XXI, Mexico City D.F. 06720,3 Mexico, and Cotton Pathology Research Unit, USDA Agricultural Research Service, College Station, Texas 778452

Received 6 July 1999/Returned for modification 14 February 2000/Accepted 8 March 2000

Sporothrix schenckii is a human pathogen that causes sporotrichosis, an important cutaneous mycosis with a worldwide distribution. It produces dark-brown conidia, which infect the host. We found that S. schenckii synthesizes melanin via the 1,8-dihydroxynaphthalene pentaketide pathway. Melanin biosynthesis in the wild type was inhibited by tricyclazole, and colonies of the fungus were reddish brown instead of black on tricyclazole-amended medium. Two melanin-deficient mutant strains were analyzed in this study: an albino that produced normal-appearing melanin on scytalone-amended medium and a reddish brown mutant that accumulated and extruded melanin metabolites into its medium. Scytalone and flaviolin obtained from cultures of the reddish brown mutant were identified by thin-layer chromatography, high-performance liquid chromatography, and UV spectra. Transmission electron microscopy showed an electron-dense granular material believed to be melanin in wild-type conidial cell walls, and this was absent in conidial walls of the albino mutant unless the albino was grown on a scytalone-amended medium. Melanized cells of wild-type S. schenckii and the albino grown on scytalone-amended medium were less susceptible to killing by chemically generated oxygen- and nitrogen-derived radicals and by UV light than were conidia of the mutant strains. Melanized conidia of the wild type and the scytalone-treated albino were also more resistant to phagocytosis and killing by human monocytes and murine macrophages than were unmelanized conidia of the two mutants. These results demonstrate that melanin protects S. schenckii against certain oxidative antimicrobial compounds and against attack by macrophages.

* Corresponding author. Mailing address: Departamento de Microbiología y Parasitología, Facultad de Medicina, UNAM, CP 04510, Mexico City D.F., Mexico. Phone: (52-5) 623-2463. Fax: (52-5) 623-2459. E-mail: haydeet{at}servidor.unam.mx.

Infection and Immunity, June 2000, p. 3696-3703, Vol. 68, No. 6
0019-9567/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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