Research Topics

Host-Pathogen Interactions, Microbial Physiology, Molecular Evolution, Protein Structure, Regulation of Gene Expression, Signal Transduction

Disease Research Interests

Infectious Diseases

B.S. (Microbiology and Biochemistry), University of Washington, 2001
Ph.D. (Microbial Pathogenesis and Molecular Microbiology), Washington University in St. Louis, 2002-2008
Postdoctoral Fellow (Pathology, Microbiology, and Immunology), Vanderbilt University, 2009-2013

Video interview

Understanding How Starvation Shapes Infection

Bacterial pathogens are a serious and growing threat to human health due to the continued emergence of antibiotic resistance, which limits our ability to treat infections. This threat is exemplified by Staphylococcus aureus, which can infect nearly every tissue in the body and is a leading cause of bone and joint infections, as well as skin and soft tissue infections. During infection pathogens must acquire all their nutrients from the host. This critical task is made more difficult as the host actively restricts essential nutrient availability during infection, starving invaders. However, how nutrient starvation impacts pathogens during infection and the adaptations that allow pathogens to overcome this host defense are unknown. Research in the Kehl-Fie laboratory is interdisciplinary leveraging microbiological approaches, biochemical studies and advanced elemental analysis to answer these questions and identify new opportunities for therapeutic intervention.

Metals and Infection

Transition metals are critical for all forms of life, with 30% of all proteins and 50% of all enzymes predicted to utilize a metal cofactor. To combat invading pathogens, the host renders sites of infection virtually devoid of these critical nutrients, a defense known as “nutritional immunity”. While classically associated with the restriction of iron, the host restricts the availability of other transition metals as well, including manganese and zinc. A critical component of the metal withholding defense of the host is the metal binding protein calprotectin. We have developed a novel series of calprotectin-based tools that enable us to study the impact of host-imposed metal starvation both in culture and during infection, and the strategies used by S. aureus and other bacteria to overcome nutritional immunity. Active areas of investigation in the Kehl-Fie laboratory relating to metals and infection include:

• The Struggle for Metals: Critical to the ability of pathogens to overcome nutritional immunity is the expression of dedicated metal uptake systems that allow invaders to fight with the host for metals. Bacteria utilize numerous import strategies to obtain metals, including transporters that directly bind the metal and those that rely on microbially produced small molecules. The latter strategy, using metallophores, was thought to be limited to facilitating the acquisition of iron. However, recent studies have revealed that S. aureus utilizes a newly identified metallophore, staphylopine, and its cognate transporter to compete with the host for zinc. Current, investigations are focused on understanding the mechanistic details of how this new family of metal importers functions and influences the interaction of S. aureus and other pathogens with the host.
  
  
• Metals and Metabolism: Glucose is the preferred energy source for S. aureus and many pathogens, but nutritional immunity inhibits the activity of metalloenzymes in glycolysis. Ongoing research is focused on understanding the role of metal-independent enzymes and alternative biochemical pathways in preserving the ability of S. aureus and other pathogens to consume glucose and generate energy when metal-starved during infection. Critical to this metabolic adaptation is the ArlRS two-component signal transduction system. Investigations are focused on elucidating how ArlRS senses the metabolic disruptions caused by host-imposed metal starvation and how activation of this global virulence regular promotes resistance to nutritional immunity and influences the outcome of infection.
  
  
• Infection and Metalloprotein Evolution: During infection pathogens must not only cope with host-imposed metal starvation, but also the oxidative burst of immune cells. All staphylococci possess a strictly manganese-dependent superoxide dismutase, SodA, which functions as a shield against oxidative stress. However, host-imposed manganese starvation inactivates this enzyme, rendering the bacteria susceptible to the oxidative burst. Differing from most staphylococci, S. aureus possesses a second closely related superoxide dismutase, SodM, that can use either manganese or iron as a cofactor. SodM enables S. aureus to retain a defense against oxidative stress when manganese-starved. It is also critical to the ability of S. aureus to cause infection and an evolutionary descendent of SodA. Current studies are focused on elucidating how the selective pressures encountered during infection shape the repertoire of metalloenzymes possessed by a pathogen and their expression. Investigations are also leveraging the high degree of identity and distinct metal specificity of SodA and SodM to determine the molecular factors that dictate metal specificity of the widely distributed iron/manganese superoxide dismutase family.

Phosphate and Infection

Phosphate critically contributes to all aspects of life, it is essential for energy storage, gene regulation, and links every base in the chromosome. While essential, overaccumulation of phosphate is toxic. As a result of these conflicting pressures bacteria tightly control phosphate import and homeostasis. Alterations in phosphate homeostasis have also been associated with changes in bacterial sensitivity to antibiotics. While these processes have been studied in model organisms, despite their relevancy to infection, few studies have examined them in pathogenic bacteria. Active areas of investigations in the Kehl-Fie laboratory relating to phosphate include:

• Phosphate Homeostasis: Proper phosphate homeostasis is critical to the ability of S. aureus to cause infection. Differing from the archetypal model Escherichia coli, S. aureus possesses an expanded number of regulatory proteins involved in controlling the activity of the master regulator of phosphate homeostasis, PhoPR (PhoBR in E. coli). Ongoing work is focused on how the increase in regulatory proteins influences the staphylococcal response to phosphate availability and contribute to infection.
  
  
• Surviving Phosphate Starvation: Relative to less pathogenic staphylococci, S. aureus expresses an expanded repertoire of phosphate uptake systems. S. aureus relies on this expanded repertoire of importers and importer-independent adaptations to survive in environments low in phosphate and to cause infection. Current studies are focused on elucidating the molecular details of how the increased number of transporters benefits S. aureus and the other adaptations that enable it to survive in phosphate-limited environments.