Biomolecular Medicine, Department of Surgery and Cancer, Department of Medicine, Imperial College, London SW7 2AZ, UK.
J Proteome Res. 2012 Jul 6;11(7):3888-96. doi: 10.1021/pr300371b. Epub 2012 Jun 11.
Nitrogen is an essential element for bacterial growth, and as such, bacteria have evolved several pathways to assimilate nitrogen and adapt to situations of nitrogen limitation. However, the adaptation of mycobacteria to nitrogen stress and the regulation of the stress response pathways is unknown. Identification of key metabolites produced by mycobacteria during nitrogen stress could therefore provide important insights into mycobacterial survival strategies. Here we used NMR-based metabolomics to monitor and quantify intracellular and extracellular metabolite levels (metabolic footprinting) in Mycobacterium smegmatis grown under nitrogen-limiting and nitrogen-rich conditions. There were several metabolic differences between the two conditions: following nitrogen run-out, there was an increase in intracellular α-ketoglutarate and a decrease in intracellular glutamine and glutamate levels. In addition, a sugar-derived compound accumulated in nitrogen-starved cells that was subsequently assigned as glucosylglycerate (GGA). Free GGA production was responsive to nitrogen stress in M. smegmatis but not to oxidative or osmotic stress; lack of a functional GGA synthesis pathway slightly reduced growth and decreased ammonium uptake rates under nitrogen-limiting conditions. Hence, GGA could contribute to the fitness of mycobacteria under nitrogen limitation.
氮是细菌生长所必需的元素，因此，细菌已经进化出几种途径来同化氮并适应氮限制的情况。然而，分枝杆菌对氮胁迫的适应以及应激反应途径的调节尚不清楚。因此，鉴定分枝杆菌在氮胁迫下产生的关键代谢物可以为分枝杆菌的生存策略提供重要的见解。在这里，我们使用基于 NMR 的代谢组学来监测和定量分枝杆菌在氮限制和氮丰富条件下生长时的细胞内和细胞外代谢物水平（代谢足迹）。两种条件之间存在几种代谢差异：在氮耗尽后，细胞内α-酮戊二酸增加，而谷氨酰胺和谷氨酸水平降低。此外，在饥饿的细胞中积累了一种源自糖的化合物，随后被指定为葡糖基甘油酸（GGA）。游离 GGA 的产生对 M. smegmatis 的氮胁迫有反应，但对氧化或渗透胁迫没有反应；缺乏功能性 GGA 合成途径会略微降低在氮限制条件下的生长速度并降低铵摄取率。因此，GGA 可以为氮限制下的分枝杆菌提供适应性。
