Collaborative Research: Mechanism of Manganese(IV) Oxide Biomineralization by a Bacterial Manganese Oxidase

锰（Mn）是一种生物学上至关重要的元素，通过许多酶的使用来维持生命，包括那些在植物中产生氧气的酶和保护许多生物体免受活性氧的侵害的酶。因此，锰循环——生物可利用的锰离子（Mn(II)）和不溶性锰氧化物（MnO2）之间的相互转化——是全球重要的。微生物在推动锰循环中发挥着重要作用：一些细菌利用二氧化锰进行呼吸，在将矿物质转化为溶解的锰（II）的过程中，而其他细菌可以氧化锰（II），形成在许多环境中都能发现的二氧化锰沉积物。后一个过程，生物矿化，是锰生物地球化学中一个鲜为人知的领域。凭借这一奖项，Bradley Tebo博士和Thomas Spiro博士将开发细菌氧化锰生物矿化的全面图景，这对于理解自然界中二氧化锰的加工方式至关重要，以及如何将这一见解应用于二氧化锰矿物在环境修复和生物能源生产中的新兴用途。该项目将加强对下一代科学家的培训，并开展外联活动，包括指导学生和旨在吸引未得到充分服务/代表性不足的初高中学生进入科学专业的项目。将制作一套艺术插图，向更广泛的受众传达该项目，并通过各种渠道提供。在许多锰（II）氧化细菌中，多铜氧化酶（MCO）酶被认为是锰（II）氧化的催化剂。在Mn（II）氧化芽孢杆菌中，休眠孢子氧化Mn（II）并形成MnO2矿物，这是由居住在孢子外孢子（包围孢子的复杂结构）中的mco催化的。然而，MnO2生成的分子机制仍有待阐明。随着第一个纯化的细菌锰氧化复合物Mnx和锰氧化细菌的收集，该项目将揭示细菌如何控制二氧化锰纳米颗粒的形成。具体来说，研究人员将描述蛋白质如何引导矿物质单元的形成，它们如何被排出到溶液中并进一步生长形成自然界中发现的矿物质，以及自然环境的复杂性-整个细胞的生物物质，络合剂和溶解的铁如何影响最终的生物矿物质。该项目高度利用了多种最先进技术的协作和集成方法，包括cryoEM， SAXS， EXAFS，液细胞TEM和计算方法，以提供氧化锰生物矿化的独特分子水平视图。此外，该项目将扩大主要用于生物医学和材料科学研究的最先进显微技术的使用，以解决具有地球化学意义的问题。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Manganese (Mn) is a biologically vital element, supporting life through its use by many enzymes, including those that produce oxygen in plants and that defend many living organisms against reactive oxygen species. Thus, the manganese cycle—the interconversion between bioavailable Mn ions (Mn(II)) and insoluble Mn oxide minerals (MnO2)—is globally important. Microorganisms play a significant part in driving the manganese cycle: some bacteria use MnO2 for respiration, in the process converting the mineral to dissolved Mn(II), while other bacteria can oxidize Mn(II), forming the MnO2 deposits that can be found in many environments. The latter process, biomineralization, is a less-understood field in manganese biogeochemistry. With this award, Dr. Bradley Tebo and Dr. Thomas Spiro will develop a comprehensive picture of bacterial manganese oxide biomineralization, which is essential for understanding how MnO2 are processed in nature, and how this insight might be applied to the burgeoning uses of MnO2 minerals in environmental remediation and bioenergy production. The project will enhance the training of the next generation of scientists and embrace outreach activities, including mentoring students and programs that seek to attract underserved/underrepresented middle and high school students to science majors. A set of artistic illustrations to communicate the project to a broader audience will be created and made available through various channels.In many Mn(II)-oxidizing bacteria, multicopper oxidase (MCO) enzymes have been implicated to be the catalysts for Mn(II) oxidation. In Mn(II)-oxidizing Bacillus species, dormant spores oxidize Mn(II) and form MnO2 minerals, catalyzed by MCOs residing in the exosporium—a complex structure that surrounds the spores. However, the molecular mechanism of MnO2 production remains to be elucidated. With the first purified bacterial manganese oxidizing complex, Mnx, and a collection of manganese-oxidizing bacteria, this project will reveal how bacteria control the formation of MnO2 nanoparticles. Specifically, investigators will characterize how the protein guides the formation of mineral units, how they are expelled into the solution and further grow to form the mineral found in nature, and how complexities of natural environment—biological matter of whole cells, complexing agents, and dissolved iron—affect the final biomineral. The project is highly leveraged through a collaborative and integrated approach of multiple state-of-the-art techniques, including cryoEM, SAXS, EXAFS, liquid-cell TEM, and computational methods to offer a unique molecular-level view of manganese oxide biomineralization. Additionally, the project will expand the use of state-of-the-art microscopic techniques, primarily used in biomedical and materials science research, to address questions of geochemical significance.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.