Collaborative Research: Assessment Of Rates And Microbial Pathways For Arsenate Reduction In Sediments

合作研究：沉积物中砷酸盐还原率和微生物途径的评估

• 批准号: 0525392
• 负责人: Chad Saltikov
• 金额: $ 20.67万
• 依托单位: University of California-Santa Cruz
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2005
• 资助国家: 美国
• 起止时间: 2005-09-15 至 2009-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0525392&HistoricalAwards=false
• 关键词: Collaborative; Research; Assessment; Rates; Microbial

EAR-0525387/EAR-0525392 Microbial processes have been widely implicated in the mobilization of arsenic (As) from geologic materials into groundwater. However, a number of unresolved questions regarding the biogeochemical redox cycling of As and microbial pathways for arsenate, As(V), reduction remain to be answered. The proposed project will address the following unresolved questions:Question 1: In a given sediment environment, is in situ As(V) reduction related to detoxification or energy acquisition pathways? What factors induce these pathways?Question 2: Under environmental conditions and at environmentally-relevant As concentrations, what are in situ rates of As(V) reduction and what factors limit these rates?Question 3: How do the varying microbial capacities (i.e., iron (Fe)(III), and/or As(V) reducing activity) influence the mobilization of As from solid phases? The proposed project will combine molecular biological and geochemical approaches to interrogate microbial redox cycling of As and its coupling with Fe cycling at field sites with natural, geothermal As inputs. Factors influencing in situ rates of As(V) reduction will be examined and the conditions that trigger this process will be identified. Molecular tools will be employed to track abundance and expression of genes involved in As(V) reduction in situ. Specifically, Question 1 will be addressed by determining the environmental conditions that affect the gene expression for the two main pathways for As(V) reduction: respiratory (arrA) and detoxification (arsC). The bacterium, Shewanella sp. str. ANA-3, which is amenable to genetic manipulation will serve as our model organism for these studies. Field studies will focus on the development and application of molecular biological techniques based on the polymerase chain reaction (PCR) to track and monitor the expression of arrA and arsC in environmental samples. Question 2 will be addressed by introducing hydrous ferric oxide (HFO) pre-equilibrated with As(V) into the ambient sediment environment using a novel gel probe in which the HFO suspension is immobilized in a highly porous gel. Withdrawal of the gels over time and analysis of the oxidation state of As associated with the HFO suspension will allow us to determine the timescale for As(V) reduction in situ. Sediment incubation experiments will also be performed to determine how As(V) reduction rates respond to changes in, for example, organic carbon substrates. We will address Question 3 by examining As mobilization from natural sediments and model solids by mutants of ANA-3 that are deficient in one or more of the genes for Fe(III) reduction and/or As(V) reduction by respiratory and/or detoxification pathways. The results of the proposed project will substantially increase our understanding of the fundamental biological and geochemical processes that influence the occurrence and mobility of As in the subsurface environment. The project will contribute to development of the science base for prediction and mitigation of human exposure to As, which is a major health issue world-wide. The proposed project will also support the training of graduate and undergraduate students, who will be exposed to a wide range of experimental methods and who will develop the skills needed to pursue interdisciplinary environmental research.

EAR-0525387/EAR-0525392微生物过程被广泛用于将地质物质中的砷(As)迁移到地下水中。然而，关于砷的生物地球化学氧化还原循环和砷的微生物途径，As(V)，还原的一些问题仍然有待回答。拟议的项目将解决以下悬而未决的问题：问题1：在给定的沉积物环境中，As(V)的原位还原是否与解毒或能量获取途径有关？是什么因素导致了这些途径？问题2：在环境条件下和与环境相关的As浓度下，As(V)的就地还原速率是多少，什么因素限制了这些速率？问题3：不同的微生物能力(即铁(Fe)(III)和/或As(V)还原活性)如何影响从固相中As的动员？拟议的项目将结合分子生物学和地球化学方法，以自然、地热为输入，在野外场地询问As的微生物氧化还原循环及其与Fe循环的耦合。将研究影响As(V)原位还原速率的因素，并确定触发这一过程的条件。分子工具将被用来跟踪参与As(V)还原的基因的丰度和表达。具体地说，问题1将通过确定影响As(V)还原的两个主要途径的基因表达的环境条件来解决：呼吸(ARRA)和解毒(ArsC)。该细菌为希瓦氏杆菌属。Str.能够进行基因操作的Ana-3将作为我们进行这些研究的模式生物。实地研究将侧重于开发和应用基于聚合酶链式反应(PCR)的分子生物技术，以跟踪和监测环境样品中ARRA和ARSC的表达。问题2将通过使用一种新型凝胶探针将与As(V)预平衡的水合三氧化二铁(HFO)引入周围沉积物环境中，其中HFO悬浮液被固定在高度多孔的凝胶中。随着时间的推移，凝胶的退出和与HFO悬浮液相关的As的氧化状态的分析将使我们能够确定As(V)在原位还原的时间尺度。还将进行沉积物培养实验，以确定As(V)的还原速率如何对例如有机碳基质的变化做出反应。我们将通过研究ANA-3突变体从自然沉积物和模拟固体中动员铁(III)还原和/或通过呼吸和/或解毒途径还原As(V)的一个或多个基因来解决问题3。拟议项目的结果将大大增加我们对影响地下环境中砷的发生和迁移的基本生物和地球化学过程的了解。该项目将有助于发展预测和减轻人类接触砷的科学基础，这是世界范围内的一个主要健康问题。拟议的项目还将支持对研究生和本科生的培训，他们将接触到各种实验方法，并将发展从事跨学科环境研究所需的技能。