DNA Repair of UV-irradiated G. lamblia Cysts Following Low and Medium Pressure UV Disinfection

最近发现紫外线（UV）辐照对高度耐氯原生动物病原体（细小隐孢子虫卵囊和贾第鞭毛虫囊）具有显著的失活能力，并且产生有害消毒副产物（DBPs）的可能性相对较低，因此作为传统化学消毒剂在水处理过程中的替代方法，最近受到了相当大的关注。事实上，紫外线消毒是符合第二阶段消毒剂和消毒副产物规则（DBPR）和长期强化地表水处理规则（LT2ESWTR）的最有前途的候选技术之一。尽管最近认识到紫外线消毒的前景，然而，在广泛使用紫外线照射作为主要消毒剂以实现微生物可接受的饮用水之前，仍有几个问题必须解决。其中一个问题是紫外线照射的水传播病原体修复其紫外线损伤DNA的能力。最近，我们的初步研究表明，在低剂量的低压紫外线照射下，在一定的修复条件下，兰氏弓形虫囊肿可以恢复其传染性。为了将这种重要的水生微生物在饮用水中的含量降低到可接受的水平，有必要对紫外线照射下的兰氏杆菌囊中DNA修复的程度和动力学进行表征，然后确定该微生物的阈值紫外线剂量。因此，本研究的目的是通过动物实验和分子生物学实验来确定低压和中压紫外线照射后兰氏革兰氏菌囊的动力学和DNA修复能力的程度，以确定紫外线照射所需的剂量（阈值剂量），从而优化紫外线消毒过程，使这种重要的水生微生物在一个可接受的水平上失活。这是对原生动物DNA修复的罕见研究之一，也可能是首次使用各种分子生物学方法表征这些微生物紫外线失活和随后修复的机制和动力学的研究。本实验收集的信息将使我们能够阐明在低压和中压紫外线照射下，紫外线照射下的蓝氏鳗损伤和修复现象的不同机制。此外，这些信息将帮助我们确定LP和MP紫外线技术控制兰氏螺旋体囊肿的阈值紫外线剂量，这将确保兰氏螺旋体囊肿的DNA修复低或不修复，从而优化紫外线照射的有效剂量，以使这种重要的水生微生物失活到保护公众健康的水平。了解每种类型紫外线灯的主要紫外线损伤和修复机制，可以为设计当前的处理设施和未来的紫外线技术提供可能，以最大限度地灭活和修复抑制兰氏囊虫和其他水生原生动物寄生虫，并通过比较其潜在优势，为水处理厂紫外线灯类型的选择提供另一个重要的标准。最后，在这项活动中收集到的信息和经验将很容易转移到其他新的和新兴的水生原生动物寄生虫的紫外线失活和修复现象的机制研究中。

0302609 Shin Ultraviolet (UV) irradiation has recently gained considerable attention as an alternative to conventional chemical disinfectants in water treatment processes after the recent discovery of its remarkable inactivation ability of the highly chlorine-resistant protozoan pathogens: Cryptosporidium parvum oocysts and Giardia lamblia cysts and relatively low potential of producing harmful disinfection byproducts (DBPs). In fact, UV disinfection is one of the most promising candidate technologies for compliance with the Stage 2 Disinfectants and Disinfection Byproduct Rule (DBPR) and Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR). Despite the recently recognized promise of UV disinfection, however, there are still several issues that must be addressed before widespread use of UV irradiation as a primary disinfectant to achieve microbially-acceptable drinking water. One such issue is the ability of UV-irradiated waterborne pathogens to repair their UV-damaged DNA. Recently, our preliminary study indicates that G. lamblia cysts can restore their infectivity when they were exposed to low doses of low pressure UV and subjected to certain repair conditions. It is important to characterize the extent and kinetics of DNA repair in UV-irradiated G. lamblia cysts and then identify the threshold UV dosage for this microorganism in order to reduce the level of this important waterborne microorganism in drinking water by an acceptable level. Therefore, the objective of this proposed activity is to determine the kinetics and the extent of the DNA repair capabilities of UV-irradiated G. lamblia cysts after exposure to from low and medium pressure UV sources with both animal and molecular biological assays order to identify required dosages (threshold dosages) of both UV irradiation and thereby optimize UV disinfection processes to inactivate this important waterborne microorganism by an appreciable and acceptable level.This proposed activity is one of the rare studies on DNA repair in protozoans and probably the first study to characterize the mechanism and kinetics of UV inactivation and subsequent repair in these microorganisms using various molecular biological methods. The information gathered in this proposed activity will enable us to elucidate the different mechanisms of UV damage and repair phenomenon in UV-irradiated G. lamblia after low and medium pressure UV exposure. Furthermore, this information will help us to determine the threshold UV dosages for control of G. lamblia cysts for both LP and MP UV technology which will ensure low or no DNA repair of G. lamblia cysts and thereby optimize the effective doses of UV irradiation to inactivate this important waterborne microorganism to levels that will protect public health. Information about the primary UV damage and repair mechanisms for each type of UV lamps would make it possible to design current treatment facilities and future UV technology for maximal inactivation and repair inhibition against G. lamblia cysts and other waterborne protozoan parasites, and also would provide another important selection criteria for UV lamp type in a water treatment plant by comparing their potential advantages. Finally, the information and experience gathered in this proposed activity with G. lamblia cysts will be easily transferred to future studies on mechanisms of UV inactivation and repair phenomena in other new and emerging waterborne protozoan parasites.