Collaborative Research: Mechanisms, Modeling, and Geochemical Consequences of Electron Flow in Acid Mine Drainage-Induced Sediments

微生物新陈代谢的物质和能量底物的转移历来被认为强烈依赖于微生物群落活跃的物理化学环境中化学物种的扩散。尽管高能底物在空间上分离，但个别有机体和微生物群落可能会调节氧化还原反应的想法现在已经开始挑战这一观点。在导电细胞外结构(如微生物纳米线)和氧化还原活性矿物相的网络中电集成的微生物群落可以促进和利用电子在远超过单个细胞(微米到米级)的尺度上的移动，称为“远距离细胞外电子传输(EET)”。FARA场EET的一个重要含义是，尽管还原剂、氧化剂甚至单个微生物本身在空间上分离，但仍可能发生生物地球化学氧化还原反应。这里提出的工作将使用酸性矿山废水(AMD)影响的系统来检查在“自然”环境中的电子流动的动力学。在一些环境中，当富含Fe(II)的AMD达到陆地表面的有氧状态时，嗜酸菌将Fe(II)氧化为Fe(III)。这些微生物活动所产生的Fe(III)(氢化物)氧化物以“铁丘”的形式堆积，几乎完全由Fe(III)相组成。据推测，由矿物相、微生物纳米线和其他导电细胞材料组成的集成导电网络促进了EET和电子通过铁丘的转移，支持了铁丘深处Fe(II)的微生物氧化，而这不是简单地通过O2扩散到铁丘中来维持的。在实验室规模的沉积物培养中，将利用野外精细的地球化学点特征，结合地学和电化学变化的测量以及导电微生物结构的详细描述，来阐明铁丘相关微生物群落介导的电子传递过程的速度、规模和程度。电子转移过程的多尺度物理模型将被用来支持和补充该系统内电子转移的实验检查，并将包括模拟微生物纳米线中的电子流动的建模，生物地理生物，以及在更大规模的系统中，如在铁丘中遇到的。这项工作的结果将加强对铁丘和AMD治疗方法中微生物介导的地球化学过程的理解。一家非营利性AMD治疗公司将作为这个项目的非资助合作者，促进AMD治疗从业者的知识转移。该项目的资金将帮助对博士后研究员、研究生和本科生进行跨学科培训，同时促进公立大学(阿克伦大学)和私立大学(南加州大学)之间的密切合作。研究生和本科生将从亚利桑那大学的麦克奈尔奖学金项目中招募。铁丘现场还将作为UA和当地学区正规课程的现场教室。

The transfer of material and energetic substrates for microbial metabolism has historically been viewed as strongly dependent on the diffusion of chemical species within the physicochemical milieu in which the microbial community is active. Ideas that individual organisms and microbial communities may mediate redox reactions despite spatial separation of energetic substrates have now begun to challenge this view. Microbial communities that are electrically integrated in a network of conductive extracellular structures (e.g. microbial nanowires) and redox-active mineral phases may facilitate and exploit the movement of electrons over scales (mm- to cm-scale) far exceeding those of the individual cells (micrometer to meter-scale), referred to as "far-afield extracellular electron transport (EET)." An important implication of farafield EET is that biogeochemical redox reactions may occur despite the spatial separation of reductant, oxidant, and even individual microorganisms themselves. The work proposed here will use an acid mine drainage (AMD)-impacted system to examine the dynamics of electron flow in a "natural" setting. In several settings, when Fe(II)-rich AMD reaches the terrestrial surface aerobic, acidophilic bacteria oxidize Fe(II) to Fe(III). The Fe(III) (hydr)oxides that result from these microbial activities accumulate as 'iron mounds,' which are composed almost exclusively of Fe(III) phases. It is hypothesized that integrated, conductive networks composed of mineral phases, microbial nanowires, and other conductive cellular material facilitate EET and the transfer of electrons through the iron mound, supporting microbiological oxidation of Fe(II) at depths within the iron mound that could not be sustained simply by diffusion of O2 into the mound. Field-based fine-scale geochemical site characterizations coupled with measurements of geo- and electro-chemical changes and detailed characterizations of electrically conductive microbial structures in laboratory-scale sediment incubations will be used to elucidate the rates, scales, and extents of electron transfer processes mediated by iron mound-associated microbial communities. Multiscale physical modeling of electron transfer processes will be used to support and supplement experimental examinations of electron transfer within this system, and will include modeling of electron flow in simulated microbial nanowires, 'biogeobatteries,' and in larger scale systems like that encountered in an iron mound. Results of this work will enhance understanding of microbially mediated geochemical processes in iron mounds and AMD treatment approaches. A non-profit AMD treatment company will serve as an unfunded collaborator on this project to facilitate knowledge transfer to AMD treatment practitioners. Funds from this project will aid in the interdisciplinary training of a post-doctoral researcher, graduate, and undergraduate students, while facilitating a strong collaboration between a public university (The University of Akron) and private university (The University of Southern California). Graduate and undergraduate students will be recruited from UA's McNair Scholars program. The iron mound field site will also serve as a field classroom for formal courses at UA and a local school district.