Regulation of dimorphism in the pathogenic fungus Histoplasma capsulatum

Abstract

Histoplasma capsulatum is a dimorphic pathogenic fungus which is the causative agent of the disease histoplasmosis. The disease is worldwide in occurrence and approximately 40 million people have been infected in the USA¹. In soil the fungus is filamentous, but in the infected host it exists as a budding yeast and it is believed that the phase transition is important in the pathogenicity. In the laboratory, the mycelial form can convert to the yeast phase when the temperature of incubation is shifted from room temperature (25 °C) to body temperature (37 °C). In this report we show that the elevated temperature initiates a series of reactions leading to changes in the intracellular level of 3′, 5′-cyclic adenosine monophosphate (cyclic AMP);the shifts in intracellular cyclic AMP levels are an important determinant of the morphological phase of the organism and therefore of its disease producing potential.