Collaborative Research: Assessment of Rates and Microbial Pathways for Arsenate Reduction in Sediments

微生物过程广泛涉及砷（As）从地质材料进入地下水的活动。 然而，一些悬而未决的问题，关于砷的生物地球化学氧化还原循环和微生物途径的砷酸盐，砷（V），还原仍然有待回答。 拟议的项目将解决以下悬而未决的问题：问题1：在一个特定的沉积物环境中，是在现场As（五）减少有关的解毒或能源获取途径？ 是什么因素导致了这些途径？问题二：在环境条件下，并在环境相关的As浓度，什么是在原位率的As（V）的减少和什么因素限制这些利率？问题3：不同的微生物能力（即，铁（Fe）（III），和/或As（V）还原活性）的影响动员的As从固相？拟议的项目将联合收割机分子生物学和地球化学的方法，询问微生物的氧化还原循环的As和它的耦合与铁循环在现场与天然，地热As输入。 影响原位As（V）还原率的因素将被检查，并确定触发这一过程的条件。 分子工具将被用来跟踪丰度和表达的基因参与As（V）减少原位。具体而言，问题1将通过确定影响As（V）减少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）。 细菌，希瓦氏菌属菌株ANA-3，这是适合遗传操作将作为我们的模式生物为这些研究。 实地研究将侧重于开发和应用基于聚合酶链反应（PCR）的分子生物学技术，以跟踪和监测环境样本中arrA和arsC的表达。 问题2将通过使用新型凝胶探针将用As（V）预平衡的水合氧化铁（HFO）引入周围沉积物环境中来解决，其中HFO悬浮液固定在高度多孔的凝胶中。 随着时间的推移，凝胶的撤回和分析的氧化态的As与HFO悬浮液将使我们能够确定的时间尺度为As（V）减少原位。 还将进行沉积物培养实验，以确定As（V）还原率如何对有机碳基质等的变化作出反应。 我们将解决问题3，通过检查作为动员自然沉积物和模型固体ANA-3的突变体是缺乏一个或多个基因的Fe（III）的减少和/或As（V）减少呼吸和/或解毒途径。 拟议的项目的结果将大大增加我们的基本生物和地球化学过程，影响地下环境中的发生和流动性的理解。 该项目将有助于发展预测和减轻人类接触砷的科学基础，这是一个全球性的重大健康问题。拟议的项目还将支持研究生和本科生的培训，他们将接触到广泛的实验方法，并将发展进行跨学科环境研究所需的技能。

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.