Collaborative Research: Sunlight Inactivation Mechanisms of Pathogenic Bacteria in Natural Waters

粪便指示细菌（FIB），如肠球菌和大肠杆菌，被用来评估海滩水质，并作为人类病原体的代理。天然水体中的FIB浓度随浓度的变化而变化，在下午三点左右通常低于测定检测极限，而在夜间则高出几个数量级，这有几个含义。首先，采集样本的时间会显著影响测量的浓度，这可能会导致符合或不符合水质标准的差异。第二，目前尚不清楚实际病原体的浓度是否也会出现这种波动，从而导致相关的健康风险。因此，获取控制FIB和相关人类病原体日波动过程的信息至关重要。阳光被认为是FIB日波动的主要原因。然而，阳光损害微生物的主要机制尚不清楚。至少有三种机制被描述：紫外线波长对细胞成分的内源性直接损伤，以及当光子被敏化剂分子吸收时，细胞内外分别产生的活性物质引起的间接内源性和外源性光失活。迄今为止的研究主要集中在FIB的光失活上，并且通常是高度经验性和地点特异性的，因此不可能概括地预测其他环境背景或其他生物体的阳光失活率。此外，关于细菌病原体的光失活的数据也非常缺乏。本项目的目的是表征FIB和一组致病菌对内源性和外源性光失活的敏感性，并建立一个光失活的定量模型。实验室实验将用于发展对控制失活过程的机制理解，并了解观察到的生物体之间差异的本质。现场和实验室数据将被纳入预测失活率的模型，该模型将通过微观研究进行测试。该模型将使用环境参数作为输入来估计细菌在阳光下的失活情况，并将有助于估计各种生物和水域的失活率，而无需进行特定地点和特定生物的研究。该项目将在几个方面促进知识的发展。这项研究将对环境中FIB和细菌病原体的命运产生重要的见解，这是保护人类健康和改善沿海水质的高度优先研究需要。这项工作将对娱乐用水的管理产生直接影响，以保护人类健康。对阳光介导的失活机制的更好理解和新的建模方法也将直接用于阳光在消毒中起主要作用的工程和自然系统，包括饮用水的太阳能消毒（SODIS）和池塘和湿地的废水处理。拟议工作的结果将与决策者和海滩管理人员分享，并将改善对人类健康的保护。调查人员将把结果整合到他们的课堂教学中。研究生和本科生将参与研究。研究人员将为高中学生开发关于阳光对雨水径流处理的影响的新课程，并为小学学生开发水与环境工程模块。

CBET 1334359/1335673Alexandria Boehm/Kara NelsonStanford University/University of California-BerkeleyFecal indicator bacteria (FIB), such as Enterococcus and Escherichia coli, are used to assess beach water quality and serve as proxies for human pathogens. FIB concentrations in natural waters vary diurnally with concentrations and are often below assay detection limits in mid-afternoon and orders of magnitude higher at night, which has several implications. First, the time the sample is collected dramatically impacts the measured concentration, which could make the difference between compliance and noncompliance with water quality standards. Second, it is not known whether the concentrations of actual pathogens, and thus associated health risk, also experience such fluctuations. Therefore, it is critical to obtain information on the processes that control the diurnal fluctuations for FIB and human pathogens of concern. Sunlight is believed to be the major cause of the diurnal fluctuations in FIB. However, the dominant mechanisms through which sunlight damages microorganisms are not well understood. At least three mechanisms have been described: endogenous direct damage to cellular components by ultraviolet wavelengths, and indirect endogenous and exogenous photoinactivation caused by reactive species generated inside and outside the cell, respectively, when photons are absorbed by sensitizer molecules. Research to date has primarily focused on FIB photoinactivation and has generally been highly empirical and site-specific so that it is not possible to generalize to predict sunlight inactivation rates in other environmental contexts or for other organisms. Additionally, there is a striking lack of data on the photoinactivation of bacterial pathogens. The objectives of this project are to characterize the susceptibility of FIB and a suite of pathogenic bacteria to endogenous and exogenous photoinactivation and develop a quantitative model for photoinactivation. Laboratory experiments will be used to develop a mechanistic understanding of processes that control inactivation, and to understand the nature of observed differences between organisms. Field and laboratory data will be incorporated into a model to predict inactivation rates, and the model will be tested using a microcosm study. The model will use environmental parameters as inputs to estimate the inactivation of bacteria by sunlight and will be useful for estimating inactivation rates for a wide range of organisms and waters without the need for site- and organism- specific studies.The project will advance knowledge in several ways. The research will yield essential insights into the fate of FIB and bacterial pathogens in the environment, a high priority research need to protect human health and improve coastal water quality. The work will have immediate implications for the management of recreational water for the protection of human health. The improved understanding of sunlight-mediated inactivation mechanisms and the new modeling approach will also be directly useful for engineered and natural systems in which sunlight plays a major role in disinfection, including solar disinfection of drinking water (SODIS) and wastewater treatment in ponds and wetlands. The results from the proposed work will be shared with policy makers and beach managers and will result in the improved protection of human health. The investigators will integrate the results into their classroom instruction. Graduate and undergraduate students will participate in the research. The investigators will develop new curriculum on the impact of sunlight on the treatment of stormwater runoff for high school students and a module on water and environmental engineering for elementary school students.