Regulation of Heme Adaptation in the Group A Streptococcus

About This Grant

Project Summary The overarching goal of this R21 proposal is to define the mechanisms by which Group A Streptococcus (GAS) senses and adapts to changing heme levels encountered during invasive infections such as bacteremia. Heme is both a critical nutrient for GAS that is kept sequestered by hemoproteins in the host as well as a toxic molecule when in excess such as following hemolysis by GAS in the blood. We hypothesize that GAS carefully monitors the levels of heme in both the extracellular and intracellular compartments and accordingly regulates the expression of heme efflux, detoxification and repair pathways. GAS likely uses heme-sensing regulatory proteins, such as two-component signal transduction systems (TCS), to coordinately control the expression of a heme defense program. In this application, we will combine molecular genetic and biochemical methods with transcriptome studies and genome-wide mutagenesis screens to identify and characterize GAS mechanisms for heme sensing and regulation as well as establish their role in GAS pathogenesis. Our preliminary RNA-seq analysis of heme stress revealed induction of sugar utilization operons for fructose, lactose and galactose that are conserved with the published responses to iron-mediated stress. Here, we expand on our published and preliminary studies to define the molecular mechanisms used by GAS to deal with heme as both a nutritional signal and a challenge during infection: Aim 1 will determine whether TCS sensor kinases are required for GAS adaptation to heme toxicity by RNA-seq and use Tn-seq to identify key regulators required for heme management. Aim 2 will investigate the regulation of a GAS sugar metabolic shift during heme stress and ask why GAS induces these metabolic pathways to protect against heme. Finally, Aim 3 will assess the role of heme-regulated signaling through TCS sensor kinases or other pathways using in vitro, ex vivo, and in vivo models of GAS bloodstream infection. This project will help reveal the fundamental impact of heme in the pathophysiology of a major human pathogen. Completion of the proposed aims will provide novel insights into the host survival strategies used by GAS and related pathogens, and will set the stage for the development of new interventions that target bacterial heme management mechanisms.