How does oxygen inhibit central metabolism in the obligate anaerobe Bacteroides thetaiotaomicron
How does oxygen inhibit central metabolism in the obligate anaerobe Bacteroides thetaiotaomicron
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DOI：
10.1046/j.1365-2958.2001.02343.x
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发表时间：
2001-03-01
影响因子：
3.6
通讯作者：
Imlay, JA
中科院分区：
文献类型：
--
作者：
Pan, N;Imlay, JA
专性厌氧的分子基础还没有很好的建立。多形拟杆菌是一种条件致病菌，不能在完全有氧的环境中生长。由于微生物的生态位反映了能源生产策略的特点，我们怀疑曝气会干扰其中央代谢。在厌氧培养基中，这种细菌将碳水化合物发酵成琥珀酸、丙酸和乙酸的混合物。当培养物暴露在空气中时，琥珀酸和丙酸的形成突然停止。体外分析表明，琥珀酸-丙酸途径的琥珀酸脱氢酶含有对超氧化物敏感的铁硫簇。在体内，当细胞通气时，铁硫酶活性下降到< 5%;在提取物经过化学处理以重建铁硫簇后，几乎所有活性都恢复了。通风对该通路的其余部分影响最小。然而，通气减少丙酮酸：铁氧还蛋白氧化还原酶（PFOR），在乙酸发酵分支的第一个酶，其厌氧活性的3%。这种含簇的酶在体外被分子氧破坏，但不被超氧化物破坏。因此，有氧生长被这些铁硫簇酶对氧化的脆弱性所阻止。重要的是，这两种酶在需氧细胞中长时间保持稳定的非活性形式;然后当细菌返回厌氧培养基时，它们迅速修复。这一结果解释了这种病原体如何从偶尔暴露于氧气中轻松恢复。
The molecular basis of obligate anaerobiosis is not well established. Bacteroides thetaiotaomicron is an opportunistic pathogen that cannot grow in fully aerobic habitats. Because microbial niches reflect features of energy-producing strategies, we suspected that aeration would interfere with its central metabolism. In anaerobic medium, this bacterium fermented carbohydrates to a mixture of succinate, propionate and acetate. When cultures were exposed to air, the formation of succinate and propionate ceased abruptly. In vitro analysis demonstrated that the fumarase of the succinate-propionate pathway contains an iron-sulphur cluster that is sensitive to superoxide. In vivo, fumarase activity fell to < 5% when cells were aerated; virtually all activity was recovered after extracts were chemically treated to rebuild iron-sulphur clusters. Aeration minimally affected the remainder of this pathway. However, aeration reduced pyruvate:ferredoxin oxidoreductase (PFOR), the first enzyme in the acetate fermentation branch, to 3% of its anaerobic activity. This cluster-containing enzyme was damaged in vitro by molecular oxygen but not by superoxide. Thus, aerobic growth is precluded by the vulnerability of these iron-sulphur cluster enzymes to oxidation. Importantly, both enzymes were maintained in a stable, inactive form for long periods in aerobic cells; they were then rapidly repaired when the bacterium was returned to anaerobic medium. This result explains how this pathogen can easily recover from occasional exposure to oxygen.