Dept. of Medical Microbiology and Hospital Epidemiology, Hannover Medical School, Hannover, 30625, Germany.
Dept. of Biochemistry, Technische Universität München, Garching, 85747, Germany.
Sci Rep. 2017 Jul 25;7(1):6484. doi: 10.1038/s41598-017-05916-7.
Mycobacterium tuberculosis (Mtb) uses alveolar macrophages as primary host cells during infection. In response to an infection, macrophages switch from pyruvate oxidation to reduction of pyruvate into lactate. Lactate might present an additional carbon substrate for Mtb. Here, we demonstrate that Mtb can utilize L-lactate as sole carbon source for in vitro growth. Lactate conversion is strictly dependent on one of two potential L-lactate dehydrogenases. A knock-out mutant lacking lldD2 (Rv1872c) was unable to utilize L-lactate. In contrast, the lldD1 (Rv0694) knock-out strain was not affected in growth on lactate and retained full enzymatic activity. On the basis of labelling experiments using [U-C]-L-lactate as a tracer the efficient uptake of lactate by Mtb and its conversion into pyruvate could be demonstrated. Moreover, carbon flux from lactate into the TCA cycle, and through gluconeogenesis was observed. Gluconeogenesis during lactate consumption depended on the phosphoenolpyruvate carboxykinase, a key enzyme for intracellular survival, showing that lactate utilization requires essential metabolic pathways. We observed that the ΔlldD2 mutant was impaired in replication in human macrophages, indicating a critical role for lactate oxidation during intracellular growth.
结核分枝杆菌（Mtb）在感染期间将肺泡巨噬细胞作为主要宿主细胞。为了应对感染，巨噬细胞会从丙酮酸氧化转变为将丙酮酸还原为乳酸。乳酸可能是 Mtb 的另一种额外碳源。在这里，我们证明 Mtb 可以将 L-乳酸作为体外生长的唯一碳源。乳酸转化严格依赖于两种潜在 L-乳酸脱氢酶之一。缺乏 lldD2（Rv1872c）的敲除突变体无法利用 L-乳酸。相比之下，lldD1（Rv0694）敲除菌株在乳酸上的生长不受影响，并且保留了完整的酶活性。根据使用 [U-C]-L-乳酸作为示踪剂的标记实验，可以证明 Mtb 有效摄取乳酸并将其转化为丙酮酸。此外，观察到从乳酸到 TCA 循环的碳通量，并通过糖异生进行。在消耗乳酸时的糖异生依赖于磷酸烯醇丙酮酸羧激酶，这是一种细胞内存活的关键酶，表明乳酸利用需要必要的代谢途径。我们观察到ΔlldD2 突变体在人巨噬细胞中的复制受到损害，表明在细胞内生长过程中乳酸氧化起着关键作用。
