Seminars & Events

Mathematics and Computer Science Division Seminar
"The Metabolic Constraints Imposed by Nitric Oxide on Invading Pathogenic Bacteria"

DATE: April 6, 2007
TIME: 10:00am
SPEAKER: Anthony Richardson, Laboratory of Medicine, University of Washington
LOCATION: Bldg: 221, Conference Room A216, Argonne
HOST: Terry Disz

Description:
Nitric oxide (NO·) is a central mediator of innate immunity that is critical for resistance to microbial pathogens such as Salmonella enterica and Staphylococcus aureus. However, the basis of NO· mediated bacteriostasis remains poorly understood. This work describes two separate approaches to determining NO·-sensitive metabolic pathways in pathogenic bacteria. First, the NO·-specific metabolic requirements were determined for S. enterica by supplementing minimal defined medium with various metabolic intermediates. It was discovered that NO· induced transient auxotrophies for both methionine (M) and lysine (K) stemming from an inability of cells undergoing nitrosative stress to produce the TCA cycle intermediate succinyl-CoA. In aerobically cultured cells, succinyl-CoA is generated by the coordinated action of a multiprotein complex, a-ketoglutarate dehydrogenase. This complex utilizes lipoamide as an essential cofactor and requires the coordinate action of several redox active thiols. Protein thiol motifs are uniquely susceptible to modification by NO· and thus a potential target of nitrosative stress in vivo. Another approach, involving the analysis of excreted metabolic end-products in S. aureus, revealed dramatic changes in the metabolism of both aerobically and anaerobically grown cells. S. aureus normally excretes acetate from the incomplete oxidation of glucose, however upon NO· exposure, acetate excretion halts, and L-lactate is produced. Similarly, S. aureus ferments glucose anaerobically producing a mixture of lactate, ethanol, and formate, but NO· exposure specifically eliminates ethanol and formate excretion. Thus, it appears that the exposure of either respiring or fermenting S. aureus to NO· results in a metabolism whereby oxidizing power (NAD+) is exclusively regenerated by the reduction of pyruvate to L-lactate. Indeed, inactivation of the inducible L-lactate dehydrogenase, ldh1, resulted in NO· sensitive cells grown either aerobically or anaerobically. Furthermore, ldh1 cells were attenuated in a murine model of infection provided the host was proficient for NO· production. This work demonstrates that host inflammatory NO· constrains metabolic pathways in pathogenic bacteria. A better understanding of the metabolic pathways available to a pathogen in the context of an infection may yield new “conditionally essential” gene products that could serve as potential drug targets.

Save the event to your calendar [schedule.ics]