Mycobacterial Metabolism and Antibiotic Research Laboratory, The Francis Crick Institute, 1 Midland Road, London, NW1 1AT, UK.
School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, 4072, Australia.
Mol Microbiol. 2019 Oct;112(4):1284-1307. doi: 10.1111/mmi.14362. Epub 2019 Aug 23.
Bacterial nutrition is an essential aspect of host-pathogen interaction. For the intracellular pathogen Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis in humans, fatty acids derived from lipid droplets are considered the major carbon source. However, many other soluble nutrients are available inside host cells and may be used as alternative carbon sources. Lactate and pyruvate are abundant in human cells and fluids, particularly during inflammation. In this work, we study Mtb metabolism of lactate and pyruvate combining classic microbial physiology with a 'multi-omics' approach consisting of transposon-directed insertion site sequencing (TraDIS), RNA-seq transcriptomics, proteomics and stable isotopic labelling coupled with mass spectrometry-based metabolomics. We discovered that Mtb is well adapted to use both lactate and pyruvate and that their metabolism requires gluconeogenesis, valine metabolism, the Krebs cycle, the GABA shunt, the glyoxylate shunt and the methylcitrate cycle. The last two pathways are traditionally associated with fatty acid metabolism and, unexpectedly, we found that in Mtb the methylcitrate cycle operates in reverse, to allow optimal metabolism of lactate and pyruvate. Our findings reveal a novel function for the methylcitrate cycle as a direct route for the biosynthesis of propionyl-CoA, the essential precursor for the biosynthesis of the odd-chain fatty acids.
细菌营养是宿主-病原体相互作用的一个重要方面。对于细胞内病原体结核分枝杆菌（Mtb），即人类结核病的病原体，来自脂滴的脂肪酸被认为是主要的碳源。然而，许多其他可溶性营养素在宿主细胞内是可用的，并且可以用作替代碳源。乳酸盐和丙酮酸在人类细胞和体液中含量丰富，特别是在炎症期间。在这项工作中，我们将经典微生物生理学与“多组学”方法（包括转座子定向插入测序（TraDIS）、RNA-seq 转录组学、蛋白质组学和稳定同位素标记与基于质谱的代谢组学）相结合，研究了 Mtb 对乳酸盐和丙酮酸的代谢。我们发现 Mtb 非常适应使用乳酸盐和丙酮酸，并且它们的代谢需要糖异生、缬氨酸代谢、三羧酸循环、GABA 支路、乙醛酸支路和甲基柠檬酸循环。后两条途径传统上与脂肪酸代谢有关，出乎意料的是，我们发现 Mtb 中的甲基柠檬酸循环反向运作，以允许乳酸盐和丙酮酸的最佳代谢。我们的发现揭示了甲基柠檬酸循环作为丙酰辅酶 A 生物合成的直接途径的新功能，丙酰辅酶 A 是奇数链脂肪酸生物合成的必需前体。
