Defining a novel photochemical pathway for the oxidation of manganese by microbes

智力价值：虽然长期以来，人们一直认为锰(II)的氧化是由微生物介导的，但细菌在这一过程中的作用仅被归因于直接的酶机制。最近，我们发现了一种替代的Mn(II)氧化途径，它是通过与细菌在异养生长过程中产生的可溶性光活性因子发生反应而发生的。这些发现在锰的循环中引入了一种新的氧化还原货币，并说明了导致锰(II)氧化的途径比最初认为的更加多样化。在这里，我们建议使用Rosebacter AzwK-3b作为模式细菌来研究这一途径。由于表层环境中玫瑰杆菌物种的数量丰度、生态多样性和地球化学相关性(如DMSP降解)，AzwK-3b将成为与环境相关的模式生物。此外，AzwK-3b在遗传上是容易处理的，并且现在可以获得基因组，从而允许对涉及光增强Mn(II)氧化的基因和基因产物进行补充研究。拟议的研究将涉及三个目标，即(1)鉴定和纯化光活性因子，(2)确定中间体和副产物，(3)确定光增强Mn(II)氧化的速率和固相产物。实现这些目标将阐明地球化学反应进程的错综复杂以及这一生物-非生物耦合过程对环境的影响。这一途径的速率和产物将与其他非生物和生物氧化机制进行比较，以确定是否存在化学和/或矿物学(生物)特征，这些特征可能有助于描述各种Mn(II)氧化机制在环境中的相对重要性。我们预测，这项研究将引入一种新的、普遍存在的次生代谢物，参与表面环境中锰的循环和不同的、活性氧化相的形成。从这项研究中收集到的信息将对我们理解锰的循环产生直接的、变革性的影响，并为未来探索微生物介导的氧化还原循环的多样化和复杂性提供基础。更广泛的影响：这项研究的更广泛的影响是环境、教育和专业性质的。Mn(II)的氧化具有广泛的环境影响，影响污染物的传输、碳的降解、营养物质的循环和基于厌氧代谢的功能。特别是，氧化锰是环境中最强的吸附剂和氧化剂之一，因此会影响几乎所有其他元素的循环。被动除锰(II)系统目前正被用于修复阿巴拉契亚地区煤矿场地含金属的酸性矿山废水。随着我们目前继续努力探索光增强Mn(II)氧化的应用方面，本文提出的研究将提供对这一途径的机理理解，理想情况下，将有助于深入了解如何优化这些修复方法，以达到峰值Mn(II)氧化和相关污染物的隔离。拟议的研究将涉及PI、一名博士后科学家和两名本科生的合作努力。本科生将在这项研究中发挥不可或缺的作用，并将在PI和博士后科学家的指导下带头完成部分实验任务。这项研究将资助3名女科学家，包括PI和目前在Pi？S实验室的一名博士后科学家和本科生。代表不足的群体也将是其他本科生招生的重点。博士后和本科生将被鼓励在哈佛大学的科学会议和当地研讨会小组中展示他们的发现。这项研究的结果将通过高知名度、同行评议的科学期刊内的出版物进一步传播给科学界。最后，这项提议将支持一名职业生涯初期教员的工作，这项研究的成果将被纳入国际和平研究所目前正在开发的本科生和研究生课程。

Intellectual Merit: While the oxidation of Mn(II) has long been recognized as microbially-mediated, the role of bacteria in this process has only been attributed to direct enzymatic mechanisms. Recently we have discovered an alternative Mn(II) oxidation pathway, which occurs via reaction with soluble, photo-active factors produced by bacteria during heterotrophic growth. These findings introduce a new redox currency in the cycling of Mn and illustrate that the pathways responsible for Mn(II) oxidation are more diverse than originally thought. Here we propose to interrogate this pathway using Roseobacter AzwK-3b as a model bacterium. Due to the numerical abundance, ecological diversity, and geochemical relevance (e.g. DMSP degradation) of Roseobacter species in surface environments, AzwK-3b will serve as an environmentally relevant model organism. Furthermore, AzwK-3b is genetically tractable and the genome is now available allowing for complementary studies on the genes and gene products involved in light enhanced Mn(II) oxidation. The proposed research will address three objectives, which are to (1) identify and purify the photo-active factor, (2) determine the intermediates and byproducts, and (3) define the rates and solid-phase products of light enhanced Mn(II) oxidation. Obtaining these objectives will elucidate the intricacies of the geochemical reaction progression and the environmental impact of this coupled biotic-abiotic process. The rates and products of this pathway will be compared to other abiotic and biotic oxidative mechanisms to determine if chemical and/or mineralogical (bio)signatures exist that may aid in delineating the relative importance of the various Mn(II) oxidative mechanisms in the environment. We predict that this research will introduce a novel, ubiquitous secondary metabolite involved in the cycling of Mn and the formation of distinct, reactive oxide phases within surface environments. Information gleaned from this research will have immediate, transformative impacts on our understanding of the cycling of Mn and provide the foundation for future explorations into the diverse and complex world of microbially mediated redox cycling. Broader Impacts: The broader impacts of this research are environmental, educational, and professional in nature. The oxidation of Mn(II) has sweeping environmental ramifications, impacting the transport of contaminants, degradation of carbon, cycling of nutrients, and function of anaerobic-based metabolisms. In particular, Mn oxides are among the strongest sorbents and oxidants in the environment and consequently impact the cycles of nearly all other elements. Passive Mn(II) removal systems are currently being employed to remediate metal-laden acidic mine drainage from coal mine sites throughout Appalachia. As we continue our current efforts to explore the applied aspects of light enhanced Mn(II) oxidation, the research proposed herein will provide the mechanistic understanding of this pathway that will, ideally, lend insight into how to optimize these remediation approaches for peak Mn(II) oxidation and sequestration of associated contaminants. The proposed research will involve a cooperative effort by the PI, a postdoctoral scientist, and two undergraduate students. The undergraduate students will play an integral role in this research and will spearhead a portion of the experimental tasks while under the guidance of the PI and postdoctoral scientist. This research will fund 3 female scientists, which includes the PI and a postdoctoral scientist and undergraduate student currently in the PI?s laboratory. Underrepresented groups will also be the focus for the other undergraduate student recruitment. The postdoc and undergraduates will be encouraged to present their findings in at scientific meetings and local seminar groups at Harvard. The results of this research will be further disseminated to the scientific community through publications within high profile, peer-reviewed scientific journals. Lastly, this proposal will support the work of an early-career faculty member and results of this research will be integrated into the undergraduate and graduate level courses currently being developed by the PI.