S. aureus is capable of withstanding nearly every facet of host innate immunity, including the production of nitric oxide (NO.) NO.-resistance is not apparent in other bacteria, including closely related coagulase negative staphylococci (CNS). We have found that the key to S. aureus NO.-resistance is the ability of this organism to evoke a metabolic state, centered around lactate metabolism, that is essentially immune to NO. S. aureus harbors three lactate dehydrogenases, one of which (Ldh1) is not present in CNS and plays a critical role in S. aureus NO.-resistance. The focus of this proposal is to understand the role of lactate-metabolism in S. aureus virulence and immune evasion.
Specific Aim 1. Establish Lqo as part of the NOX-cycle, an essential pathway for S. aureus virulence. We identified a gene encoding the S. aureus lacate:quinone oxidoreductase (Lqo) and demonstrated its role in virulence. Here we test hypotheses explaining why a fourth lactate-utilizing enzyme in S. aureus is so critical to pathogenesis. We will establish the NOX cycle, a metabolic pathway relying on both Ldh1 and Lqo that actually allows S. aureus to use host NO. for energy production. We will also structurally and biochemically characterize Lqo, the founder of a new family of enzymes found only among the staphylococci.
Specific Aim 2. Unravel the multiple roles for lactate metabolism in S. aureus pathogenesis. Unlike CNS, S. aureus exhibits lactate "enantiomer preference" during NO.-stress and produces copious amounts of the L-isomer, the only form of lactate able to participate in the NOX cycle. We will define the regulatory mechanisms resulting in peak expression of ldh1, the S. aureus-specific lactate dehydrogenase responsible for "enantiomer preference". We will also test hypotheses aimed at explaining the curious observation that both L- and D-lactate production are required for S. aureus virulence. We have observed that genes involved in S. aureus lactate metabolism are either not present or are differentially regulated in CNS. Thus, the new acquisition and altered regulation of genes involved in S. aureus lactate-metabolism provides a model for the "Metabolic Evolution" of an emerging pathogen. These incremental evolutionary changes provided S. aureus with the metabolic flexibility necessary to thrive within an immunocompetent host and must have coincided with the acquisition of canonical virulence factors for this pathogen to emerge.

Public Health Relevance

Staphylococcus aureus, the organism responsible for MRSA infections, is one of the most dangerous and costly bacterial pathogens afflicting Americans today. In order to resist the effects of our immune system and cause disease, this bacterium must adopt a unique form of metabolism involving lactate, an organic acid commonly associated with spoiled milk. We propose that a thorough understanding of lactate-metabolism in S. aureus will lead to new targets for the development of antibiotics used to combat this important human pathogen.

Agency
National Institute of Health (NIH)
Institute
National Institute of Allergy and Infectious Diseases (NIAID)
Type
Research Project (R01)
Project #
5R01AI093613-04
Application #
8613430
Study Section
Bacterial Pathogenesis Study Section (BACP)
Program Officer
Huntley, Clayton C
Project Start
2011-03-01
Project End
2016-02-29
Budget Start
2014-03-01
Budget End
2015-02-28
Support Year
4
Fiscal Year
2014
Total Cost
$327,483
Indirect Cost
$102,483
Name
University of North Carolina Chapel Hill
Department
Microbiology/Immun/Virology
Type
Schools of Medicine
DUNS #
608195277
City
Chapel Hill
State
NC
Country
United States
Zip Code
27599
Sapp, April M; Mogen, Austin B; Almand, Erin A et al. (2014) Contribution of the nos-pdt operon to virulence phenotypes in methicillin-sensitive Staphylococcus aureus. PLoS One 9:e108868
Kumar, Nag S; Dullaghan, Edie M; Finlay, B Brett et al. (2014) Discovery and optimization of a new class of pyruvate kinase inhibitors as potential therapeutics for the treatment of methicillin-resistant Staphylococcus aureus infections. Bioorg Med Chem 22:1708-25
Crooke, Adrianne K; Fuller, James R; Obrist, Markus W et al. (2013) CcpA-independent glucose regulation of lactate dehydrogenase 1 in Staphylococcus aureus. PLoS One 8:e54293
Thurlow, Lance R; Joshi, Gauri S; Clark, Justin R et al. (2013) Functional modularity of the arginine catabolic mobile element contributes to the success of USA300 methicillin-resistant Staphylococcus aureus. Cell Host Microbe 13:100-7