IMPACT OF SUPEROXIDE ON THE PHYSIOLOGY OF MODEL BACTERIA

氧化应激与多种人类疾病有关。它 也是细菌致病的关键，因为氧气限制 嗜氧微生物的毒力和巨噬细胞使用氧化剂 来攻击细菌入侵者。因此，重要的是要实现 氧物种损伤机制的分子理解 以及细胞用来保护自己的战术。这个 我们实验室的长期目标是使用模型解决这些问题 细菌作为研究对象。我们目前的目标是： (1)探讨大鼠氧耐量异常的分子基础。 拟杆菌Tetaiotaomicron.初步数据显示，B.theta是 寄售于厌氧菌的部分原因是它的富马酸酶，一种关键的铁- 硫磺脱水酶，在空气中失去活性。如果这一想法得到证实， 然后，第二个问题将被探讨：为什么空气会使这种 在B.theta中有铁-硫簇，但在E.Coli中没有？ (2)解释超氧化物歧化酶缺陷型E. Coli.SOD突变体不能合成支链氨基酸或 分解分解不可发酵的碳源，它们很快就会遭受损失 诱变。这些特征已经被铁-硫化物清楚地解释了 群集已损坏。然而，这些突变体也需要降低硫和 芳香氨基酸。间接证据表明，这些 表型也是从簇状损伤进化而来的。 (3)解释大肠杆菌合成两种乌头酸酶的原因。在氧化过程中 应激大肠杆菌诱导一种抗超氧化物歧化的同工酶取代 一个不稳定的人。这就回避了一个问题：为什么要保持一个不稳定的同工酶 全?一个答案可能微不足道--主要的乌头酸酶是 运动学上的优势--但更有趣的可能性是 主要的乌头酸酶失活在铁质时期是有益的。 饿死了。 (4)揭示SoxRS调节子的防御机制 氧化应激细胞。SoxRS调节子诱导几种酶 这对超氧化物压力下的细胞有明显的好处，但 其他人的目的则更加模糊。有可能的是，一些 后者的酶有助于修复受损的铁-硫簇。其他，这样的 作为葡萄糖-6-磷酸脱氢酶，只有在 这些药物的一些毒性是由NADPH耗竭引起的 而不是来自活性氧物种。

Oxidative stress has been linked to a variety of human pathologies. It is also critical to bacterial pathogenesis, both because oxygen limits the virulence of microaerophiles and because macrophages use oxidants to attack bacterial invaders. Therefore it is important to achieve a molecular understanding to the mechanisms by which oxygen species damage cells and to the tactics that cells employ to defend themselves. The long-term goal of our lab is to resolve these issues using model bacteria as study subjects. Our current aims are: (1) To explore the molecular basis of the oxygen intolerance of Bacteroides thetaiotaomicron. Preliminary data suggest that B. theta is consigned to anaerobiosis in part because its fumarase, a key iron- sulfur dehydratase, loses activity in air. If this idea is confirmed, then a second problem will be explored: Why does air inactivate such iron-sulfur clusters in B. theta but not in E. coli? (2) To explain unsolved phenotypes of superoxide dismutase-deficient E. coli. SOD mutants cannot synthesize branched-chain amino acids or catabolize non-fermentable carbon sources, and they suffer rapid mutagenesis. These traits have been clearly explained by iron-sulfur cluster damaged. However, these mutants also require reduced sulfur and aromatic amino acids. Circumstantial evidence suggests that these phenotypes, too, evolve from cluster damage. (3) To explain why E. coli synthesizes two aconitases. During oxidative stress E. Coli induces a superoxide-resistant isozyme to replace the labile one. This begs the question: Why maintain a labile isozyme at all? One answer may be trivial--that the primary aconitase is kinetically superior--but a more interesting possibility is that the inactivation of the major aconitase is beneficial during periods of iron starvation. (4) To uncover the mechanisms by which the SoxRS regulon defends oxidatively stressed cells. The SoxRS regulon induces several enzymes that provide obvious benefits to superoxide-stressed cells, but the purposes of others are more obscure. It is plausible that some of the latter enzymes help to repair damaged iron-sulfur clusters. Other, such as glucose-6-phosphate dehydrogenases, may be understandable only if some of the toxicity of these drugs arises from NADPH depletion rather than from reactive oxygen species.