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

CBET 1334359/1335673 Alexandria Boehm/Kara Nelson Stanford University/University of California-BerkeleyFecal Indicator细菌，如肠球菌和大肠杆菌，用于评估海滩水质，并作为人类病原体的替代品。天然水中的纤维蛋白浓度随浓度的变化而变化，通常在下午三点左右低于化验检测限值，在晚上高出数量级，这有几个方面的影响。首先，采集样本的时间极大地影响了测量的浓度，这可能会导致水质标准符合和不符合之间的差异。其次，目前还不知道实际病原体的浓度是否也经历了这种波动，从而导致了相关的健康风险。因此，获得控制FIB和人类关注病原体日波动的过程的信息是至关重要的。阳光被认为是FIB日波动的主要原因。然而，阳光破坏微生物的主要机制还没有被很好地理解。至少有三种机制已被描述：紫外线对细胞成分的内源性直接损伤，以及当光敏剂分子吸收光子时，细胞内外产生的活性物质分别导致内源性和外源光失活的间接机制。到目前为止，研究主要集中在FIB光灭活上，一般都是高度经验性的和特定地点的，因此不可能在其他环境背景或其他生物体中推广预测太阳光灭活速率。此外，关于细菌病原体的光灭活数据也非常缺乏。本项目的目的是表征FIB和一系列病原菌对内源和外源光灭活的敏感性，并建立光灭活的定量模型。实验室实验将被用来发展对控制失活的过程的机械理解，并理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合并到一个模型中，以预测灭活率，该模型将使用微观研究进行测试。该模型将使用环境参数作为输入，以估计阳光对细菌的灭活，并将有助于估计广泛生物和水域的灭活率，而不需要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。这项研究将对FIB和细菌病原体在环境中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所需的高度优先研究。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。对阳光介导的灭活机制和新的建模方法的更好的理解也将直接有助于工程和自然系统，其中阳光在消毒中发挥主要作用，包括太阳能饮用水消毒(SODIS)和池塘和湿地的废水处理。拟议工作的结果将与政策制定者和海滩管理人员分享，并将改善对人类健康的保护。调查人员将把结果融入他们的课堂教学中。研究生和本科生将参与这项研究。研究人员将为高中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.