Ubiquinone 8 (coenzyme Q8 or Q8) mediates electron transfer within the aerobic respiratory chain, mitigates oxidative stress, and contributes to gene expression in Escherichia coli In addition, Q8 was proposed to confer bacterial osmotolerance by accumulating during growth at high osmotic pressure and altering membrane stability. The osmolyte trehalose and membrane lipid cardiolipin accumulate in E. coli cells cultivated at high osmotic pressure. Here, Q8 deficiency impaired E. coli growth at low osmotic pressure and rendered growth osmotically sensitive. The Q8 deficiency impeded cellular O2 uptake and also inhibited the activities of two proton symporters, the osmosensing transporter ProP and the lactose transporter LacY. Q8 supplementation decreased membrane fluidity in liposomes, but did not affect ProP activity in proteoliposomes, which is respiration-independent. Liposomes and proteoliposomes prepared with E. coli lipids were used for these experiments. Similar oxygen uptake rates were observed for bacteria cultivated at low and high osmotic pressures. In contrast, respiration was dramatically inhibited when bacteria grown at the same low osmotic pressure were shifted to high osmotic pressure. Thus, respiration was restored during prolonged growth of E. coli at high osmotic pressure. Of note, bacteria cultivated at low and high osmotic pressures had similar Q8 concentrations. The protection of respiration was neither diminished by cardiolipin deficiency nor conferred by trehalose overproduction during growth at low osmotic pressure, but rather might be achieved by Q8-independent respiratory chain remodeling. We conclude that osmotolerance is conferred through Q8-independent protection of respiration, not by altering physical properties of the membrane.

中文翻译：

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在高渗透压下进行培养可赋予大肠杆菌泛素8独立的呼吸保护作用。

泛醌8（辅酶Q8或Q8）介导有氧呼吸链内的电子转移，减轻氧化应激，并有助于大肠杆菌中的基因表达。另外，有人提出Q8通过在高渗透压下生长并改变膜来积累细菌渗透压。稳定。渗透液海藻糖和膜脂质心磷脂在高渗透压下培养的大肠杆菌细胞中积聚。在此，Q8缺乏会在低渗透压下损害大肠杆菌的生长，并使生长对渗透敏感。Q8缺乏症阻止细胞吸收氧气，也抑制了两个质子同向转运蛋白（渗透压转运蛋白ProP和乳糖转运蛋白LacY）的活性。Q8补充剂降低了脂质体中的膜流动性，但并未影响蛋白脂质体中的ProP活性，这是与呼吸无关的。用大肠杆菌脂质制备的脂质体和蛋白脂质体用于这些实验。对于在低和高渗透压下培养的细菌，观察到相似的氧气吸收率。相反，当以相同的低渗透压生长的细菌转移到高渗透压时，呼吸被显着抑制。因此，在高渗透压下大肠杆菌的长期生长过程中，呼吸得以恢复。值得注意的是，在低和高渗透压下培养的细菌具有相似的Q8浓度。在低渗透压下生长期间，心磷脂缺乏既不会减弱对呼吸的保护，也不会因海藻糖的过量产生而赋予呼吸保护，而是可以通过独立于Q8的呼吸链重塑来实现。