Identifying genes required for growth in Histoplasma capsulatum under osmotic stress conditions

Angela Grass, The College of Wooster

Abstract

Histoplasma capsulatum is a dimorphic fungi that causes the respiratory illness histoplasmosis in humans. This illness is caused by the yeast cellular state of H. capsulatum residing in the lungs of the victim. While the environmental pressure of 37_C has been identified as the trigger for yeast morphology, the proteins and genes required to make such a change have yet to be identified. Only a handful of proteins, DRK1 (a histidine kinase), RYP1, RYP2 and RYP3 (DNA binding proteins), have been identified as being involved in the change from the mycelial to yeast states. Through sequence similarity, DRK1 has been identified as similar to a histidine kinase found within the yeast eukaryote Saccharomyces cerevisiae, known as SLN1. SLN1 has a distinct role within S. cerevisiae's adaption to osmotic stress. This research presents evidence that H. capsulatum can withstand osmotic stress similar to S. cerevisiae. It also suggests that the ability to adapt to osmotic stress is made possible, at least in part, by the role of DRK1 and the potential that the RYP proteins are within the same protein cascade as DRK1.