Metabolism of host-derived glycolytic products by Mycobacterium tuberculosis requires five metabolic pathways

Bacterial nutrition is a key aspect of host-pathogen interaction and bacteria must adapt to use nutrients available in the host. Lipid droplets-derived fatty acids are considered the major intracellular carbon source for Mycobacterium tuberculosis (Mtb), an intracellular pathogen causing Tuberculosis disease. However, many other (and more soluble) substrates are available in vivo and may represent alternative carbon sources. Lactate and pyruvate are rather abundant in human cells and fluids and represent two possible candidates. In this work, we employed a “multi-omics” approach (Transposon Directed Insertion Site Sequencing (TraDIS), RNA-seq transcriptomics, proteomics and stable isotopic labelling coupled with mass spectrometry-based metabolomics) and classic microbial physiology to study Mtb metabolism of lactate and pyruvate. We discovered that Mtb is well adapted to use lactate and pyruvate as sole carbon sources and that it requires gluconeogenesis, Krebs cycle, GABA shunt, glyoxylate shunt and methylcitrate cycle for their metabolism. These latter are traditionally associated with fatty acid metabolism and unexpectedly, we found that methylcitrate cycle operates in reverse. This latter discovery changes the role of this pathway making it a direct route for the biosynthesis of propionyl-CoA, the essential precursor for the biosynthesis of odd-chain fatty acids, abundantly present in Mtb cell envelope.