Baez Antonino, Shiloach Joseph
Laboratorio Ecología Molecular Microbiana, Centro de Investigaciones en Ciencias Microbiológicas (CICM)-Instituto de Ciencias (IC), Benemérita Universidad Autónoma de Puebla (BUAP), Puebla, Mexico.
Biotechnology Core Laboratory, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD, 20892, USA.
Antonie Van Leeuwenhoek. 2017 Jan;110(1):115-124. doi: 10.1007/s10482-016-0781-7. Epub 2016 Oct 18.
The damaging effect of high oxygen concentration on growth of Escherichia coli is well established. Over-oxygenation increases the intracellular concentration of reactive oxygen species (ROS), causing the destruction of the [4Fe-4S] cluster of dehydratases and limiting the biosynthesis of both branched-chain amino acids and nicotinamide adenine dinucleotide. A key enzyme that reduces the damaging effect of superoxide is superoxide dismutase (SOD). Its transcriptional regulation is controlled by global transcription regulators that respond to changes in oxygen and iron concentrations and pH. Production of biological compounds from E. coli is currently achieved using cultures grown to high cell densities which require oxygen-enriched air supply. It is, therefore, important to study the effect of over-oxygenation on E. coli metabolism and the bacterial protecting mechanism. The effect of over-oxygenation on the superoxide dismutase regulation system was evaluated in cultures grown in a bioreactor by increasing the oxygen concentration from 30 to 300 % air saturation. Following the change in the dissolved oxygen (DO), the expression of sodC, the periplasmic CuZn-containing SOD, and sodA, the cytosolic Mn-containing SOD, was higher in all the tested strains, while the expression of the sodB, the cytosolic Fe-containing SOD, was lower. The down-regulation of the sodB was found to be related to the activation of the small RNA RyhB. It was revealed that iron homeostasis, in particular ferric iron, was involved in the RyhB activation and in sodB regulation but not in sodA. Supplementation of amino acids to the culture medium reduced the intracellular ROS accumulation and reduced the activation of both SodA and SodC following the increase in the oxygen concentration. The study provides evidence that at conditions of over-oxygenation, sodA and sodC are strongly regulated by the amount of ROS, in particular superoxide; and sodB is regulated by iron availability through the small RNA RyhB. In addition, information on the impact of NADH, presence of amino acids and type of iron on SOD regulation, and consequently, on the ROS concentration is provided.
高氧浓度对大肠杆菌生长的破坏作用已得到充分证实。过度氧化会增加细胞内活性氧（ROS）的浓度，导致脱水酶的[4Fe-4S]簇遭到破坏，并限制支链氨基酸和烟酰胺腺嘌呤二核苷酸的生物合成。一种能降低超氧化物破坏作用的关键酶是超氧化物歧化酶（SOD）。其转录调控由响应氧气、铁浓度及pH值变化的全局转录调节因子控制。目前，利用培养至高细胞密度的培养物来实现大肠杆菌生物化合物的生产，而这需要供应富氧空气。因此，研究过度氧化对大肠杆菌代谢及细菌保护机制的影响具有重要意义。通过将生物反应器中培养物的氧气浓度从30%空气饱和度提高到300%空气饱和度，评估了过度氧化对超氧化物歧化酶调节系统的影响。在溶解氧（DO）发生变化后，所有测试菌株中周质含铜锌超氧化物歧化酶sodC和胞质含锰超氧化物歧化酶sodA的表达均升高，而胞质含铁超氧化物歧化酶sodB的表达则降低。发现sodB的下调与小RNA RyhB的激活有关。研究表明，铁稳态，尤其是三价铁，参与了RyhB的激活和sodB的调节，但不参与sodA的调节。向培养基中补充氨基酸可减少细胞内ROS的积累，并降低氧气浓度升高后SodA和SodC的激活。该研究提供的证据表明，在过度氧化条件下，sodA和sodC受ROS量，尤其是超氧化物的强烈调节；而sodB则通过小RNA RyhB受铁可用性的调节。此外，还提供了关于NADH、氨基酸的存在以及铁的类型对SOD调节进而对ROS浓度影响的信息。
