Heat Shock and Adaptation During Temperature-Activated Dimorphism in the Fungus Histoplasma capsulatum

Abstract

Histoplasma capsulatum is the causative agent of histoplasmosis, a systemic fungal disease worldwide in occurrence, and the most common respiratory mycotic infection affecting humans and animals (Schwarz 1981). Several fungi, in particular those pathogenic such as H.capsulatum, Blastomyces dermatitidis, Paracoccidioides brasiliensis etc., can assume a filamentous or unicellular morphology in response to changes in the environmental conditions (Maresca and Kobayashi 1989). H.capsulatum grows as mycelia in soil while the yeast phase is the only form present in patients. In laboratory conditions, dimorphism is directly and reversibly controlled by temperature changes. The temperature-induced transition and the events in establishment of infection seem to be intimately correlated. In fact, the temperature works not only as a signal for adaptation through the induction of a heat shock-like phenomenon, but also in triggering the phase transition. The role that the heat shock response plays during the differentiation process and in the adaptation to high temperature in H.capsulatum will be discussed here.