Gene expression in Pseudomonas aeruginosa exposed to hydroxyl-radicals

Recent studies have shown the efficiency of hydroxyl radicals generated via ultraviolet (UV)-based advanced oxidation processes (AOPs) combined with hydrogen peroxide (UV/H₂O₂) as a treatment process in water. The effects of AOP treatments on bacterial gene expression was examined using Pseudomonas aeruginosa strain PAO1 as a model-organism bacterium. Many bacterial genes are not expressed all the time, but their expression is regulated. The regulation is at the beginning of the gene, in a genetic region called “promoter” and affects the level of transcription (synthesis of messenger RNA) and translation (synthesis of protein). The level of expression of the regulated genes can change as a function of environmental conditions, and they can be expressed more (induced, upregulated) or less (downregulated). Exposure of strain PAO1 to UV/H₂O₂ treatment resulted in a major change in gene expression, including elevated expression of several genes. One interesting gene is PA3237, which was significantly upregulated under UV/H₂O₂ as compared to UV or H₂O₂ treatments alone. The induction of this gene is probably due to formation of radicals, as it is abolished in the presence of the radical scavenger tert-butanol (TBA) and is seen even when the bacteria are added after the treatment (post-treatment exposure). Upregulation of the PA3237 promoter could also be detected using a reporter gene, suggesting the use of such genetic constructs to develop biosensors for monitoring AOPs in water-treatment plants. Currently biosensors for AOPs do not exist, consequently impairing the ability to monitor these processes on-line according to radical exposure in natural waters.