Blastomycosis

Habitat

Blastomyces dermatitidis is a pathogenic Ascomycete (family: Onygenaceae) that exists in nature as a sporulating mold and converts to a large, 15 to 20 micron, thick-walled yeast form at elevated temperatures. This dimorphic fungus is closely related to Histoplasma capsulatum, Coccidioides immitis and Paracoccidioides brasiliensis. Although the ecology of B. dermatitidis is still the subject of debate, these phylogenetic relatives of B. dermatitidis grow naturally in soils, often involving or requiring the presence of animal excreta. The favored substrate of B. dermatitidis appears to be material with a high organic content, with the assumption frequently being made that it, too, must grow within the soil. Some studies suggest that decaying wood might be its reservoir, and others have pointed out a strong association between bodies of water and the exogenous saprophytic source of B. dermatitidis.

Blastomyces dermatitidis is endemic in the central United States in and around the Ohio and Mississippi River Valleys, though blastomycosis has been reported in parts of Canada and in the southeastern United States. African varieties of B. dermatitidis have been isolated and described, but these strains lack antigens that are characteristic of North American B. dermatitidis and produce a variant pattern of blastomycosis consisting largely of chronic cutaneous lesions.

Biology

Thermally regulated dimorphism represents the single most defining trait of B. dermatitidis and related dimorphic fungi such as H. capsulatum. These agents reversibly differentiate between mold and yeast phases via a morphologic transition that can be controlled and induced in vitro by growing the fungi at 25°C (mold) or 37°C (yeast). Transition from the mold to yeast form is an absolute requirement for pathogenesis.

Conidia constitute the infectious form of the fungus. After inhalation into the lungs of animals or humans, they swell and germinate into the pathogenic yeast form. Unchecked proliferation in turn results in blastomycosis, a systemic mycosis that can become life threatening when it is undiagnosed or untreated. Acute blastomycosis is occasionally self-limiting, but more frequently progresses to produce pulmonary disease with the potential for dissemination to other organs, skin and bone.

Excerpts from Trends in Microbiology 2002;10:25-30.

Sequencing plan

B. dermatitidis is the second dimorphic fungal genus sequenced at The Genome Institute. Our goal is to generate a WGS draft sequence of B. dermatitidis and use it to infer genomic and evolutionary relatedness between Histoplasma capsulatum isolates G217B and G186A-R. See our Histoplasma capsulatum web page for more information. The collaborators for this project were Dr. Bruce Klein, the University of Wisconsin and Dr. Bill Goldman, Department of Molecular Microbiology, Washington University. Funds for this project were provided by the National Institute for Allergy and Infectious Diseases (NIAID) of the National Institutes of Health (NIH).

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Contacts

Name	Affiliation
Patrick Minx	The Genome Institute, Washington University School of Medicine
Bruce Klein	University of Wisconsin-Madison School of Medicine and Public Health

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Sequences & Maps

Assemblies

Name	Date	Description	Blast DBs
Blastomyces_dermatitidis-3.0	Feb 15, 2005	3.74X	contigs supercontigs
Blastomyces_dermatitidis-7.2	Feb 13, 2008	3.7X	contigs supercontigs

EST

Name	Date	Description	Blast DBs
Blastomyces_dermatitidis EST		Mycelial and yeast phase	Myc_3730 Myc_454 Yst_3730 Yst_454

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