Role of the methylcitrate cycle in Mycobacterium tuberculosis metabolism, intracellular growth, and virulence

• Published in: Molecular microbiology Vol. 60; no. 5; pp. 1109 - 1122
• Main Authors: Muñoz‐Elías, Ernesto J., Upton, Anna M., Cherian, Joseph, McKinney, John D.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.06.2006; Blackwell Science
• Subjects: Animals; Bacteria; Biological and medical sciences; Bone Marrow Cells - cytology; Bone Marrow Cells - metabolism; Carbon-Carbon Lyases - classification; Carbon-Carbon Lyases - genetics; Carbon-Carbon Lyases - metabolism; Cells, Cultured; Citrate (si)-Synthase - genetics; Citrate (si)-Synthase - metabolism; Citric Acid - chemistry; Citric Acid - metabolism; Escherichia coli Proteins - genetics; Escherichia coli Proteins - metabolism; Fatty acids; Female; Fundamental and applied biological sciences. Psychology; Fungi; Genes; Hydro-Lyases - genetics; Hydro-Lyases - metabolism; Isocitrate Lyase - classification; Isocitrate Lyase - genetics; Isocitrate Lyase - metabolism; Isoenzymes - classification; Isoenzymes - genetics; Isoenzymes - metabolism; Macrophages - cytology; Macrophages - metabolism; Male; Metabolism; Mice; Mice, Inbred C57BL; Microbiology; Molecular Sequence Data; Molecular Structure; Mycobacterium tuberculosis; Mycobacterium tuberculosis - genetics; Mycobacterium tuberculosis - physiology; Pathogens; Phylogeny; Propionates - metabolism; Microbiology; Mycobacterium tuberculosis; Mycobacteriales; Virulence; Mycobacteriaceae; Bacteria; Actinomycetes; Intracellular; Metabolism
• DOI: 10.1111/j.1365-2958.2006.05155.x
• ISSN: 0950-382X

Summary Growth of bacteria and fungi on fatty acid substrates requires the catabolic β‐oxidation cycle and the anaplerotic glyoxylate cycle. Propionyl‐CoA generated by β‐oxidation of odd‐chain fatty acids is metabolized via the methylcitrate cycle. Mycobacterium tuberculosis possesses homologues of methylcitrate synthase (MCS) and methylcitrate dehydratase (MCD) but not 2‐methylisocitrate lyase (MCL). Although MCLs share limited homology with isocitrate lyases (ICLs) of the glyoxylate cycle, these enzymes are thought to be functionally non‐overlapping. Previously we reported that the M. tuberculosis ICL isoforms 1 and 2 are jointly required for growth on fatty acids, in macrophages, and in mice. ICL‐deficient bacteria could not grow on propionate, suggesting that in M. tuberculosis ICL1 and ICL2 might function as ICLs in the glyoxylate cycle and as MCLs in the methylcitrate cycle. Here we provide biochemical and genetic evidence supporting this interpretation. The role of the methylcitrate cycle in M. tuberculosis metabolism was further evaluated by constructing a mutant strain in which prpC (encoding MCS) and prpD (encoding MCD) were deleted. The ΔprpDC strain could not grow on propionate media in vitro or in murine bone marrow‐derived macrophages infected ex vivo; growth under these conditions was restored by complementation with a plasmid containing prpDC. Paradoxically, bacterial growth and persistence, and tissue pathology, were indistinguishable in mice infected with wild‐type or ΔprpDC bacteria.