title: ¹³C metabolic flux analysis identifies an unusual route for pyruvate dissimilation in mycobacteria which requires isocitrate lyase and carbon dioxide fixation.
abstract: Mycobacterium tuberculosis requires the enzyme isocitrate lyase (ICL) for growth and virulence in vivo. The demonstration that M. tuberculosis also requires ICL for survival during nutrient starvation and has a role during steady state growth in a glycerol limited chemostat indicates a function for this enzyme which extends beyond fat metabolism. As isocitrate lyase is a potential drug target elucidating the role of this enzyme is of importance; however, the role of isocitrate lyase has never been investigated at the level of in vivo fluxes. Here we show that deletion of one of the two icl genes impairs the replication of Mycobacterium bovis BCG at slow growth rate in a carbon limited chemostat. In order to further understand the role of isocitrate lyase in the central metabolism of mycobacteria the effect of growth rate on the in vivo fluxes was studied for the first time using ¹³C-metabolic flux analysis (MFA). Tracer experiments were performed with steady state chemostat cultures of BCG or M. tuberculosis supplied with ¹³C labeled glycerol or sodium bicarbonate. Through measurements of the ¹³C isotopomer labeling patterns in protein-derived amino acids and enzymatic activity assays we have identified the activity of a novel pathway for pyruvate dissimilation. We named this the GAS pathway because it utilizes the Glyoxylate shunt and Anapleurotic reactions for oxidation of pyruvate, and Succinyl CoA synthetase for the generation of succinyl CoA combined with a very low flux through the succinate--oxaloacetate segment of the tricarboxylic acid cycle. We confirm that M. tuberculosis can fix carbon from CO₂ into biomass. As the human host is abundant in CO₂ this finding requires further investigation in vivo as CO₂ fixation may provide a point of vulnerability that could be targeted with novel drugs. This study also provides a platform for further studies into the metabolism of M. tuberculosis using ¹³C-MFA.
authors.affiliation: School of Biomedical and Molecular Sciences, University of Surrey, Guildford, United Kingdom.
authors.forename: Dany J V
authors.initials: DJ
authors.lastname: Beste
authors.forename: Bhushan
authors.initials: B
authors.lastname: Bonde
authors.forename: Nathaniel
authors.initials: N
authors.lastname: Hawkins
authors.forename: Jane L
authors.initials: JL
authors.lastname: Ward
authors.forename: Michael H
authors.initials: MH
authors.lastname: Beale
authors.forename: Stephan
authors.initials: S
authors.lastname: Noack
authors.forename: Katharina
authors.initials: K
authors.lastname: Nöh
authors.forename: Nicholas J
authors.initials: NJ
authors.lastname: Kruger
authors.forename: R George
authors.initials: RG
authors.lastname: Ratcliffe
authors.forename: Johnjoe
authors.initials: J
authors.lastname: McFadden
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D002245:Carbon Dioxide / Q000378:metabolism*; D002247:Carbon Isotopes; D017353:Gene Deletion; D006801:Humans; D007522:Isocitrate Lyase / Q000235:genetics / Q000378:metabolism*; D009163:Mycobacterium bovis / Q000201:enzymology / Q000235:genetics; D009169:Mycobacterium tuberculosis / Q000201:enzymology* / Q000235:genetics / Q000472:pathogenicity; D019289:Pyruvic Acid / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D002247:Carbon Isotopes; D002245:Carbon Dioxide; D019289:Pyruvic Acid; D007522:Isocitrate Lyase