Collaborative Research: Elucidating the role of animal heme peroxidase and organic complexing agents in the formation of Mn oxides by a Roseobacter bacterium

锰（Mn）的循环和锰氧化物矿物的形成具有广泛的环境和健康影响。锰是一种微量营养素，负责广泛的必需酶的功能，包括参与光合作用和破坏有毒细胞氧化剂的酶。Mn的氧化形式，可溶性Mn（III）和Mn（IV）基氧化物矿物，是碳和金属污染物的循环和封存的关键参与者。微生物的直接和间接活动在很大程度上是锰氧化物矿物形成的原因，但这些生物为什么以及如何产生这些矿物仍不清楚。动物血红素过氧化物酶（AHP）的酶已经牵连在锰（II）的氧化和锰氧化物的形成由一些细菌。此外，一些细菌和真菌形成的锰氧化物与细胞外产生的超氧化物（一种氧自由基）有关。Mn（II）和超氧化物之间的反应导致形成过氧化氢和Mn（III），而不是Mn（IV）氧化物矿物。过氧化氢的去除允许小的Mn氧化物沉淀，但它们生长成较大的颗粒（例如在环境中发现的那些颗粒）受到阻碍，并且似乎取决于由生物体产生的有机化合物的存在。很明显，锰氧化物的形成涉及一个复杂的非生物和生物反应网络，涉及蛋白质、超氧化物和有机分子。因此，该项目将解开AHP，超氧化物和有机分子在丰富和广泛的Rosebellum分支内的海洋细菌形成锰氧化物的关系。PI将通过破坏锰氧化物形成细菌中编码三种AHP酶的基因，并将这些相同的基因插入不产生锰氧化物的相关细菌中，来鉴定AHP在锰氧化物形成中的作用。研究人员将比较和监测锰的种类、超氧化物和过氧化氢的水平，以及野生型和转基因细菌产生的锰结合有机分子的存在和组成，以揭示锰氧化物形成的必要条件。锰作为土壤和沉积物释放温室气体二氧化碳的主要控制因素，因为它是少数几种可以将难降解碳降解为更不稳定形式从而阻碍其长期螯合和稳定的化合物之一。此外，由于锰氧化物的形成需要特别强的氧化剂，锰现在被认为是一个有前途的古代表，它可以作为早期地球和其他行星上高氧条件的关键指标。然而，对锰循环的科学理解从根本上是不完整的，在负责锰氧化物矿物形成的过程中存在重大知识空白。该项目将获得有助于缩小这些差距的基本信息，从而改进碳循环的预测模型，帮助清理受污染生态系统的战略，并为解释早期地球和外星岩石记录提供信息。该项目还将涉及PI直接指导和协助一名MS研究生和3名本科生进行与该项目相关的研究。此外，PI将为K-12教师开发和举办夏季研讨会，向他们介绍地质微生物学领域，并协助他们制定课程和课堂活动，将这些知识转化为课堂上的学生。

The cycling of manganese (Mn) and formation of manganese oxide minerals has sweeping environmental and health implications. Manganese is a micronutrient, responsible for the function of a broad range of essential enzymes including those involved in photosynthesis and destruction of toxic cellular oxidants. The oxidized forms of Mn, both soluble Mn(III) and Mn(IV)-based oxide minerals, are key players in the cycling and sequestration of carbon and metal contaminants. The direct and indirect activity of microorganisms is largely responsible for the formation of Mn oxide minerals, yet why and how these organisms produce these minerals remains unclear. Animal heme peroxidase (AHP) enzymes have been implicated in the oxidation of Mn(II) and formation of Mn oxides by a number of bacteria. Further, the formation of Mn oxides by some bacteria and fungi has been linked to superoxide, an oxygen radical, produced outside the cell. Reaction between Mn(II) and superoxide results in the formation of hydrogen peroxide and Mn(III), not Mn(IV) oxide minerals. Removal of the hydrogen peroxide allows for the precipitation of small Mn oxides, yet their growth to larger particles such as those found in the environment is impeded and appears dependent upon the presence of organic compounds produced by the organism. It is clear that the formation of Mn oxides involves a complex network of abiotic and biotic reactions involving protein(s), superoxide, and organic molecules. Accordingly, this project will unravel the relationship between AHP, superoxide, and organic molecules in the formation of Mn oxides by a marine bacterium within the abundant and widespread Roseobacter clade. The PIs will identify the role of AHP in Mn oxide formation by disrupting genes encoding three AHP enzymes in a Mn oxide forming bacterium and also inserting these same genes into a related bacterium that does not make Mn oxides. The PIs will compare and monitor the species of Mn, the levels of superoxide and hydrogen peroxide, and the presence and composition of Mn-binding organic molecules produced by the wild-type and genetically modified bacteria to unravel the conditions necessary for Mn oxide formation.Manganese is receiving increasing attention as a dominant control on the release of the greenhouse gas carbon dioxide from soils and sediments, as it is one of a select few compounds that can degrade recalcitrant carbon to more labile forms thus hindering its long-term sequestration and stabilization. Further, since the formation of Mn oxides requires particularly strong oxidants, Mn is now regarded as a promising paleoproxy where it may serve as a key indicator of high oxygen conditions on early Earth and other planets. Yet, a scientific understanding of the Mn cycle is fundamentally incomplete, with major knowledge gaps in the processes responsible for the formation of Mn oxide minerals. This project will obtain essential information helping to close these gaps, thereby improving predictive models of carbon cycling, aiding strategies for cleaning up contaminated ecosystems, and informing interpretations of the early Earth and extraterrestrial rock record. This project will also involve the PIs directly mentoring and assisting an MS graduate student and 3 undergraduate students in research associated with this project. Furthermore, the PIs will develop and host a summer workshop for K-12 teachers to introduce them to the field of geomicrobiology and assist them in the development of curriculum and in-class activities to translate this knowledge to students in the classroom.