Ehrt Lab Research
Intracellular survival strategies
To better understand the molecular basis for the ability of M. tuberculosis (Mtb) to survive within macrophages and resist host defense mechanisms we identify and characterize mutants that are susceptible to stresses encountered by the pathogen during persistence within its host (1-3). The analysis of the molecular mechanisms underlying the loss of stress resistance and loss of virulence of these mutants can help better understand the intracellular environment encountered by Mtb and reveal how the pathogen resists host defense mechanisms.
Paucibacillary Mtb infection
Tuberculosis (TB) chemotherapy often fails to sterilize Mtb, resulting in individuals at risk of relapse TB. Taking advantage of conditional gene expression systems (4-6), we have, together with Dirk’s group, developed models of paucibacillary (low levels of bacilli) infection in mice. Investigating the mechanisms required by Mtb to persist during paucibacillary TB in mice can identify new points of vulnerability, which could be targeted to kill populations that escape current chemotherapy in people with latent Mtb infection. These models are also being used to investigate the host immune components that control paucibacillary Mtb and uncover mechanisms of control or disease progression in TB.
Metabolic adaptation and nutrient acquisition in vivo
Metabolic adaptations to the nutritional environments encountered within the host have been a major focus of the analysis of Mtb-host interactions and are relevant to the identification and evaluation of new TB drug targets. We apply genetic, biochemical and - in close collaboration with Kyu Rhee - metabolomic approaches to investigate the metabolic pathways that Mtb requires to establish and maintain chronic infections (7-12). During infection, the host suppresses mycobacterial replication and dissemination by enclosing bacteria within phagosomes, thereby reducing access to nutrients. We have implemented genetic strategies to identify nutrient acquisition pathways in Mtb during infection.
Vaccination with Mycobacterium bovis BCG can induce protection but is too ineffective to prevent the spread of TB. In collaboration with Dirk, Eric Rubin and Sarah Fortune at Harvard Medical School, Joanne Flynn at the University of Pittsburgh and Bob Seder at the NIH, we use genetic strategies to generate improved TB vaccines. We pursue different strategies building on BCG and testing if virulent Mtb could be converted into a safe and protective vaccine strain.
1. Vandal OH, Pierini LM, Schnappinger D, Nathan CF, Ehrt S (2008) A membrane protein preserves intrabacterial pH in intraphagosomal Mycobacterium tuberculosis. Nat Med 14(8):849–854.
2. Goodsmith N, et al. (2015) Disruption of an M. tuberculosis Membrane Protein Causes a Magnesium-dependent Cell Division Defect and Failure to Persist in Mice. PLoS Pathog 11(2):e1004645–23.
3. Botella H, et al. (2017) Mycobacterium tuberculosis protease MarP activates a peptidoglycan hydrolase during acid stress. EMBO J 36(4):536–548.
4. Ehrt S, et al. (2005) Controlling gene expression in mycobacteria with anhydrotetracycline and Tet repressor. Nucleic Acids Res 33(2):e21.
5. Kim J-H, et al. (2013) A genetic strategy to identify targets for the development of drugs that prevent bacterial persistence. Proc Natl Acad Sci USA 110(47):19095–19100.
6. Lin K, et al. (2016) Mycobacterium tuberculosis Thioredoxin Reductase Is Essential for Thiol Redox Homeostasis but Plays a Minor Role in Antioxidant Defense. PLoS Pathog 12(6):e1005675–20.
7. Marrero J, Rhee KY, Schnappinger D, Pethe K, Ehrt S (2010) Gluconeogenic carbon flow of tricarboxylic acid cycle intermediates is critical for Mycobacterium tuberculosis to establish and maintain infection. Proc Natl Acad Sci USA 107(21):9819–9824.
8. Marrero J, Trujillo C, Rhee KY, Ehrt S (2013) Glucose Phosphorylation Is Required for Mycobacterium tuberculosis Persistence in Mice. PLoS Pathog 9(1):e1003116.
9. Puckett S, et al. (2014) Inactivation of Fructose-1,6-Bisphosphate Aldolase Prevents Optimal Co-catabolism of Glycolytic and Gluconeogenic Carbon Substrates in Mycobacterium tuberculosis. PLoS Pathog 10(5):e1004144–11.
10. Ganapathy U, et al. (2015) Two enzymes with redundant fructose bisphosphatase activity sustain gluconeogenesis and virulence in Mycobacterium tuberculosis. Nature Communications 6:1–12.
11. Puckett S, et al. (2017) Glyoxylate detoxification is an essential function of malate synthase required for carbon assimilation in Mycobacterium tuberculosis. Proc Natl Acad Sci USA 114(11):E2225–E2232.
12. Ruecker N, et al. (2017) Fumarase Deficiency Causes Protein and Metabolite Succination and Intoxicates Mycobacterium tuberculosis. Cell Chemical Biology 24(3):306–315.