The Characterization of a Hybrid Histidine Kinase in the Pathogenic Dimorphic Fungus Histoplasma capsulatum

Mary Rebecca Moreci, The College of Wooster


Histoplasma capsulatum is a pathogenic fungus prevalent in the Ohio-Mississippi River Valley area. H. capsulatum is the causative agent for the upper-respiratory disease Histoplasmosis. The key to H. capsulatum's pathogenicity is its dimorphism; upon temperature change from 25°C to 37°C, the fungus undergoes a morphological transition from mycelial growth to yeast-like buds, enabling it to infect mammalian lungs. This phase change occurs through the expression of cellular response genes initiated by histidine kinases. Histidine kinases have previously been identified as environmental sensor proteins that activate cellular response genes in two-component signal (TCS) transduction in fungi, plants, and bacteria. Dimorphism-regulating histidine kinase (DRK1) is a histidine kinase identified as the activator of virulence factors and yeast-phase growth genes for H. capsulatum. Previous research identified several putative hybrid histidine kinases (HcHHKs) in addition to DRK1 in H. capsulatum. The aim of this project was to characterize the role and function of HcHHK2 in H. capsulatum. Literature suggests the absence of histidine kinases would inhibit successful fungal growth under varying environmental conditions. Phylogenetic analysis of HcHHK2 suggests HcHHK2 functions as an ethylene receptor, providing a starting point for further research. A real-time reverse-transcriptase PCR experiment was designed and is currently being used to determine the morphological form of H. capsulatum that best expresses HcHHK2. Standard PCR run on cDNA from H. capsulatum grown at 25 °C and 37 °C provided preliminary results suggesting that HcHHK2 is only expressed during yeast-phase growth. An RNA interference (RNAi) construct is currently being built to mediate a gene knockdown of HcHHK2 to test under varying environmental conditions, but is still being tested due cloning difficulties.


© Copyright 2011 Mary Rebecca Moreci