Iron is an essential nutrient for nearly all organisms because it serves as a co-factor for many proteins, often in the form of iron, heme or iron-sulfur (Fe-S) clusters. Yet iron is often scarce in the environment placing its acquisition and usage under control of some of the most highly regulated pathways in biology. We are studying two key regulators of iron metabolism in the facultative anaerobe Escherichia coli, IscR and Fur. We have found that the activity and genes that are transcribed by IscR and Fur change significantly under anaerobic conditions. Thus, this project seeks to understand how this change occurs and how it impacts the utilization of iron under anaerobic conditions. Our first goal is to understand how activity of Fur, the global regulator of iron homeostasis in this and other bacteria, is regulated under anaerobic conditions. We will determine if an increase in free iron under anaerobic conditions can explain the increased activity of Fur at select weak affinity promoters in the absence of oxygen. We discovered that IscR is a novel DNA-binding protein that recognizes different sequence motifs in its apo- and [2Fe-2S]-bound forms. A second goal of this proposal is to define the biochemical and structural properties of IscR that allow metal binding to alter its DNA-binding specificity under anaerobic conditions. In this funding period, we will extend our studies of Fur and IscR from the well-studied K12 laboratory E. coli strain to the clinically relevant uropathogenic E. coli CFT073. Uropathogenic E.coli is a major cause of urinary tract infections and studies in model systems have linked both Fur and IscR to pathogenesis by this strain. Our results will provide important new insight as to how function of Fur and IscR are altered under anaerobic conditions. In addition, understanding how the activity of these regulators are coordinated to control iron and Fe-S homeostasis will allow us to develop new strategies to control the growth of commensal and pathogenic microbes in the anaerobic environment of the host.

Public Health Relevance

Iron is an essential metal but most of what we know about the pathways that maintain iron homeostasis is influenced by its reactivity with O2. Iron homeostasis is also intertwined with microbial pathogenesis and host colonization due to the scarcity of iron. Thus, pathogens must win the battle for iron to cause disease, and some pathogens inhabit O2 limited environments. The proposed research will develop a better understanding of anaerobic iron homeostasis in well-studied and clinically relevant bacteria.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
5R01GM115894-02
Application #
9113049
Study Section
Prokaryotic Cell and Molecular Biology Study Section (PCMB)
Program Officer
Reddy, Michael K
Project Start
2015-08-01
Project End
2019-04-30
Budget Start
2016-05-01
Budget End
2017-04-30
Support Year
2
Fiscal Year
2016
Total Cost
Indirect Cost
Name
University of Wisconsin Madison
Department
Biochemistry
Type
Schools of Medicine
DUNS #
161202122
City
Madison
State
WI
Country
United States
Zip Code
53715
Mettert, Erin L; Kiley, Patricia J (2018) Reassessing the Structure and Function Relationship of the O2 Sensing Transcription Factor FNR. Antioxid Redox Signal 29:1830-1840
Carey, Jeffrey N; Mettert, Erin L; Roggiani, Manuela et al. (2018) Regulated Stochasticity in a Bacterial Signaling Network Permits Tolerance to a Rapid Environmental Change. Cell 173:196-207.e14
Beauchene, Nicole A; Mettert, Erin L; Moore, Laura J et al. (2017) O2 availability impacts iron homeostasis in Escherichia coli. Proc Natl Acad Sci U S A 114:12261-12266