Systems-Level Metabolic Flux Profiling Elucidates a Complete, Bifurcated Tricarboxylic Acid Cycle in Clostridium acetobutylicum
Systems-Level Metabolic Flux Profiling Elucidates a Complete, Bifurcated Tricarboxylic Acid Cycle in Clostridium acetobutylicum
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DOI：
10.1128/jb.00490-10
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发表时间：
2010-09-01
影响因子：
3.2
通讯作者：
Rabinowitz, Joshua D.
中科院分区：
文献类型：
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作者：
Amador-Noguez, Daniel;Feng, Xiao-Jiang;Rabinowitz, Joshua D.
专性厌氧菌对土壤和人体肠道的整体代谢有重要贡献。然而，这些细菌的代谢途径仍知之甚少。利用同位素示踪剂、质谱分析和定量通量模型，在此我们直接绘制了丙酮丁醇梭菌的代谢途径，这是一种土壤细菌，其主要发酵产物包括生物燃料丁醇和氢气。虽然基因组注释表明缺乏大多数三羧酸（TCA）循环酶，但我们的结果表明该细菌具有一个完整的、尽管是分叉的TCA循环；草酰乙酸通过柠檬酸/α - 酮戊二酸以及苹果酸/富马酸流向琥珀酸。我们的研究还深入了解了葡萄糖分解代谢和氨基酸生物合成所利用的途径，并揭示该生物体的一碳代谢不同于模式微生物，涉及可逆的丙酮酸脱羧以及使用丙酮酸作为生物合成反应的一碳供体。这项研究首次对丙酮丁醇梭菌的TCA循环和中心代谢进行了体内表征。我们的结果确定了完整的TCA循环在专性厌氧生物中的作用，并证明了用同位素示踪研究补充基因组注释对于确定多种微生物代谢途径的重要性。
Obligatory anaerobic bacteria are major contributors to the overall metabolism of soil and the human gut. The metabolic pathways of these bacteria remain, however, poorly understood. Using isotope tracers, mass spectrometry, and quantitative flux modeling, here we directly map the metabolic pathways of Clostridium acetobutylicum, a soil bacterium whose major fermentation products include the biofuels butanol and hydrogen. While genome annotation suggests the absence of most tricarboxylic acid (TCA) cycle enzymes, our results demonstrate that this bacterium has a complete, albeit bifurcated, TCA cycle; oxaloacetate flows to succinate both through citrate/alpha-ketoglutarate and via malate/fumarate. Our investigations also yielded insights into the pathways utilized for glucose catabolism and amino acid biosynthesis and revealed that the organism's one-carbon metabolism is distinct from that of model microbes, involving reversible pyruvate decarboxylation and the use of pyruvate as the one-carbon donor for biosynthetic reactions. This study represents the first in vivo characterization of the TCA cycle and central metabolism of C. acetobutylicum. Our results establish a role for the full TCA cycle in an obligatory anaerobic organism and demonstrate the importance of complementing genome annotation with isotope tracer studies for determining the metabolic pathways of diverse microbes.