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Infection and Immunity, December 2001, p. 7671-7678, Vol. 69, No. 12
0019-9567/01/$04.00+0   DOI: 10.1128/IAI.69.12.7671-7678.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Potential Role for Extracellular Glutathione-Dependent Ferric Reductase in Utilization of Environmental and Host Ferric Compounds by Histoplasma capsulatum

Michelle M. Timmerman and Jon P. Woods*

Department of Medical Microbiology and Immunology, Microbiology Doctoral Training Program, University of Wisconsin, Madison, Wisconsin 53706

Received 2 August 2001/Returned for modification 30 August 2001/Accepted 13 September 2001

The mammalian host specifically limits iron during Histoplasma capsulatum infection, and fungal acquisition of iron is essential for productive infection. H. capsulatum expresses several iron acquisition mechanisms under iron-limited conditions in vitro. These components include hydroxamate siderophores, extracellular glutathione-dependent ferric reductase enzyme, extracellular nonproteinaceous ferric reductant(s), and cell surface ferric reducing agent(s). We examined the relationship between these mechanisms and a potential role for the extracellular ferric reductase in utilization of environmental and host ferric compounds through the production of free, soluble Fe(II). Siderophores and ferric reducing agents were coproduced under conditions of iron limitation. The H. capsulatum siderophore dimerum acid and the structurally similar basidiomycete siderophore rhodotorulic acid acted as substrates for the ferric reductase, and rhodotorulic acid removed Fe(III) bound by transferrin. The mammalian Fe(III)-binding compounds hemin and transferrin served both as substrates for the ferric reductase and as iron sources for yeast-phase growth at neutral pH. In the case of transferrin, there was a correlation between the level of iron saturation and efficacy for both of these functions. Our data are not consistent with an entirely pH-dependent mechanism of iron acquisition from transferrin, as has been suggested to occur in the macrophage phagolysosome. The foreign siderophore ferrioxamine B also acted as a substrate for the ferric reductase, while the foreign siderophore ferrichrome did not. Both ferrioxamine and ferrichrome served as iron sources for yeast- and mold-phase growth, the latter presumably by some other acquisition mechanism(s).

* Corresponding author. Mailing address: Department of Medical Microbiology and Immunology, 420 SMI, 1300 University Ave., University of Wisconsin, Madison, WI 53706-1532. Phone: (608) 265-6292. Fax: (608) 265-6717. E-mail: jpwoods{at}facstaff.wisc.edu.

Infection and Immunity, December 2001, p. 7671-7678, Vol. 69, No. 12
0019-9567/01/$04.00+0   DOI: 10.1128/IAI.69.12.7671-7678.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


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