Related Experiment Video
Updated: Aug 7, 2026
Passive Administration of Monoclonal Antibodies Against H. capsulatum and Others Fungal Pathogens
Published on: February 15, 2011
Calcium dependence and binding in cultures of Histoplasma capsulatum
1Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
Abstract:
Histoplasma capsulatum is a pathogenic fungus with two distinct morphologies and lifestyles. The saprophytic form of this organism, a mold, thrives in soil and is especially abundant in the Ohio and Mississippi River valleys. Its parasitic counterpart, a yeast, colonizes phagolysosomes of mammalian macrophages. We have observed a major difference in the calcium requirements of the two forms of Histoplasma, potentially implicating the phagolysosome as a calcium-limiting compartment. Deprivation of calcium by the addition of EGTA to culture media inhibited the growth of mycelial H. capsulatum but had no effect on yeast growth in vitro. In addition, yeasts released a calcium-binding protein (CBP) detectable by a 45CaCl2 blotting technique. CBP was a major component of yeast culture supernatant and was also detectable by ruthenium red staining, another assay for calcium-binding activity. Conversely, mycelial H. capsulatum did not produce CBP, a finding that correlates with the dependence of mycelia on calcium for growth. We also describe here the purification of CBP from yeast culture supernatant by reversed-phase high-pressure liquid chromatography.
Insights
Histoplasma capsulatum yeast forms release calcium-binding protein (CBP) and do not require external calcium, unlike mold forms. This suggests the phagolysosome is calcium-limited for fungal growth.
Area of Science:
- Medical Mycology
- Cell Biology
- Biochemistry
Background:
- Histoplasma capsulatum exists as a soil mold and an intracellular yeast.
- The yeast form resides within mammalian macrophage phagolysosomes.
- Calcium ion homeostasis is critical for cellular functions.
Purpose of the Study:
- To investigate the differential calcium requirements of Histoplasma capsulatum morphotypes.
- To identify potential mechanisms for yeast survival in calcium-limited phagolysosomes.
- To characterize calcium-binding molecules produced by H. capsulatum.
Main Methods:
- Growth assays of mycelial and yeast forms in calcium-depleted media (EGTA).
- Detection of calcium-binding proteins using 45CaCl2 blotting and ruthenium red staining.
- Purification of calcium-binding protein (CBP) via reversed-phase HPLC.
Main Results:
- Mycelial growth was inhibited by calcium deprivation, while yeast growth was unaffected.
- Yeast, but not mycelial, forms secreted a calcium-binding protein (CBP).
- CBP was identified as a major component in yeast culture supernatant.
Conclusions:
- The phagolysosome may be a calcium-limiting environment for Histoplasma.
- Yeast's ability to thrive in low calcium conditions is linked to CBP production.
- CBP plays a role in yeast adaptation and survival within macrophages.
Related Concept Videos
01:16Calmodulin-dependent Signaling
The Ca2+-CaM complex does not have enzymatic activity by itself. Instead, the complex binds downstream target proteins, including membrane proteins or enzymes,...
01:21Skeleton and Calcium Homeostasis