Université de Lyon, Université Lyon 1, CNRS, UMR 5256, IRCELYON, Institut de recherches sur la catalyse et l'environnement de Lyon, F-69626 Villeurbanne, France.
Water Res. 2012 Jun 15;46(10):3208-18. doi: 10.1016/j.watres.2012.03.019. Epub 2012 Mar 17.
In order to compare the disinfection potential of photocatalysis and photochemistry, the effects of these two processes on bacteria in water were investigated under exposure to UV-A and UV-C. The well-known bacterial model Escherichia coli (E. coli) was used as the experimental organism. Radiation exposure was produced with an HPK 125 W lamp and the standard TiO(2) Degussa P-25 was used as the photocatalyst. Firstly, the impact of photocatalysis and photochemistry on the cultivability of bacterial cells was investigated. UV-A radiation resulted in low deleterious effects on bacterial cultivability but generated colonies of size smaller than average. UV-C photocatalysis demonstrated a greater efficiency than UV-A photocatalysis in altering bacterial cultivability. From a cultivability point of view only, UV-C radiation appeared to be the most deleterious treatment. A rapid epifluorescence staining method using the LIVE/DEAD Bacterial Viability Kit was then used to assess the modifications in bacterial membrane permeability. UV-A radiation did not induce any alterations in bacterial permeability for 420 min of exposure whereas only a few minutes of exposure to UV-C radiation, with the same total radiance intensity, induced total loss of permeability. Moreover, after 20 and 60 min of exposure to UV-C and UV-A photocatalysis respectively, all bacteria lost their membrane integrity, suggesting that the bacterial envelope is the primary target of reactive oxygen species (ROS) generated at the surface of TiO(2) photocatalyst. These results were further confirmed by the formation of malondialdehyde (MDA) during the photocatalytic inactivation of bacterial cells and suggest that destruction of the cell envelope is a key step in the bactericidal action of photocatalysis. The oxidation of bacterial membrane lipids was also correlated with the monitoring of carboxylic acids, which can be considered as representatives of lipid peroxidation by-products. Finally, damages to bacterial morphology induced by UV-C photocatalysis and photochemistry were investigated through Scanning electron microscopy (SEM). Bacterial cells were observed on microscopy pictures at exposure durations corresponding to a loss of cultivability. After 90 min of exposure to UV-C radiation, bacterial cells showed little alteration of their outer membrane whereas they suffered deep deleterious damages under UV-C photocatalysis exposure.
为了比较光催化和光化学的消毒潜力，在暴露于 UV-A 和 UV-C 下研究了这两种过程对水中细菌的影响。使用著名的细菌模型大肠杆菌（E. coli）作为实验生物。使用 HPK 125 W 灯进行辐射照射，并使用标准的 TiO(2)Degussa P-25 作为光催化剂。首先，研究了光催化和光化学对细菌细胞可培养性的影响。UV-A 辐射对细菌可培养性的有害影响较小，但产生的菌落大小小于平均值。UV-C 光催化在改变细菌可培养性方面比 UV-A 光催化更有效。仅从可培养性的角度来看，UV-C 辐射似乎是最有害的处理方法。然后使用快速荧光染色法，使用 LIVE/DEAD 细菌活力试剂盒，评估细菌膜通透性的变化。在暴露 420 分钟的情况下，UV-A 辐射不会引起细菌通透性的任何变化，而仅在暴露于 UV-C 辐射几分钟的情况下，相同的总辐射强度就会导致通透性完全丧失。此外，分别暴露于 UV-C 和 UV-A 光催化 20 和 60 分钟后，所有细菌均失去了膜完整性，这表明细菌包膜是 TiO(2)光催化剂表面生成的活性氧（ROS）的主要靶标。这些结果通过在细菌细胞的光催化失活过程中形成丙二醛（MDA）进一步得到证实，并表明破坏细胞包膜是光催化杀菌作用的关键步骤。细菌膜脂质的氧化也与羧酸的监测相关，羧酸可以被认为是脂质过氧化产物的代表。最后，通过扫描电子显微镜（SEM）研究了 UV-C 光催化和光化学引起的细菌形态损伤。在与可培养性丧失相对应的暴露时间观察显微镜图片上的细菌细胞。在暴露于 UV-C 辐射 90 分钟后，细菌细胞的外膜几乎没有变化，而在 UV-C 光催化暴露下，它们遭受了严重的有害损伤。
