The Importance of Anaerobic Manganese Respiration in the Cycling of Nitrogen in Sediments

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。氮是地球上生命的基本元素，但海洋中的固定氮相对稀缺。同时，全球氮收支难以平衡，这表明未知的硝化和反硝化反应可能占水库之间的氮大通量。在过去的十年中，新的微生物转化氮已被发现使用地球化学，培养和分子方法，和基因负责氧化铵已被发现在各种各样的原核生物。在这些过程中，厌氧氨氧化，在亚硝酸盐或硝酸盐的存在下厌氧氧化铵为N2，可能有助于30-50%的海洋环境中的反硝化作用。其他有利的生态途径假设在沉积物中氮的转化中发挥重要作用，包括铁和锰耦合的硝化和反硝化。该项目的总体目标是证明锰还原原核生物通过厌氧氧化铵提供亚硝酸盐和硝酸盐的替代来源，从而在氮循环中发挥重要作用。包括我们在内的几项研究得出结论，锰偶联厌氧硝化发生在海洋沉积物中，尽管仍然缺乏这种过程的直接证据，纯菌株也尚未分离出来。一系列的培养与沉积物将补充培养独立的分子系统发育研究，以确定在培养显示MnO 2依赖的硝化活性的优势微生物物种。这些孵育将补充培养方法，以分离催化该反应的纯培养物或混合培养物。本研究将证明，异化锰还原在厌氧硝化中起着重要的作用，并最终通过厌氧氨氧化过程的反硝化。反硝化作用和锰的异化还原在沉积物碳循环中起着重要作用，因此本研究中发现的新过程将对我们理解全球碳循环产生更广泛的影响。这项研究还将完善成岩模型，并扩大参与氮循环的微生物过程的数量，以帮助更准确地平衡氮收支。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). Nitrogen is an essential element for life on Earth, yet fixed nitrogen is relatively scarce in the oceans. Simultaneously, global nitrogen budgets are difficult to balance, suggesting unknown nitrification and denitrification reactions may account for a large flux of nitrogen between reservoirs. Over the last decade, new microbial transformations of nitrogen have been discovered using geochemical, cultivation, and molecular approaches, and genes responsible for the oxidation of ammonium have been found in a wide variety of prokaryotes. Among these processes, anammox, which anaerobically oxidizes ammonium to N2 in the presence of nitrite or nitrate, may contribute to 30-50% of denitrification in marine environments. Other thermodynamically favorable pathways hypothesized to play a significant role in the transformation of nitrogen in sediments include iron- and manganese-coupled nitrification and denitrification. The overall objective of this project is to demonstrate that manganese-reducing prokaryotes play a significant role in the nitrogen cycle by providing, through anaerobic oxidation of ammonium, an alternative source of nitrite and nitrate to denitrifying and nitrate- reducing microorganisms. Several studies, including ours, have concluded that manganese- coupled anaerobic nitrification occurs in marine sediments, though direct evidence for such processes is still lacking and pure strains have yet to be isolated. A series of incubations with sediments will be complemented with cultivation-independent molecular phylogenetic studies to identify the dominant microbial species in incubations displaying MnO2-dependent nitrifying activities. These incubations will be supplemented with a cultivation approach to isolate pure or mixed cultures catalyzing this reaction. This study will demonstrate that dissimilatory manganese reduction plays a significant role in anaerobic nitrification and, ultimately, denitrification through the anammox process. Denitrification and the dissimilatory reduction of manganese play a significant role in the cycling of carbon in sediments, thus the new processes identified in this study will have broader implications on our understanding of the global carbon cycle. This study will also refine diagenetic models and expand the number of microbial processes involved in the nitrogen cycle to help balance nitrogen budgets more accurately.