Collaborative Research: Acquisition of nitrogenase metal cofactors in soils: role of metallophores and limitation of N2-fixation

智力优势：氮气的固定完全由细菌和古细菌使用固氮酶来实现，固氮酶含有铁和钼作为金属辅因子，其最活跃的形式是铁和钒，或者只以铁的替代形式存在。本项目的目的是阐明细菌从土壤中获取铁、钼和钒的机制和动力学如何限制或控制氮气固定速率。固氮细菌产生铁载体(或铁载体？)与外部介质中的铁结合，并吸收生成的铁载体络合物。我们最近的工作表明，铁载体实际上是金属载体？用于钼、钒和铁的吸收。因此，各种固氮酶金属辅因子的生物获取依赖于它们与细菌金属载体的结合。该项目围绕两个主要假设进行组织：1.自由生活的固氮菌分泌金属载体，这种金属载体在捕获限制固氮的金属(Mo、V或Fe)方面特别有效；2.由于与其他金属竞争金属载体结合和土壤中的稀缺性，钼天生就很难获得，自由生活的固氮菌通常使用替代固氮酶，特别是V-固氮酶来固定氮。这些假设将通过实验室和现场实验相结合的方式进行验证。实地研究将集中在钼可能限制的部位，并利用分子生物学技术来确定替代氮素。广泛的影响：一名博士后研究员、一名研究生和几名本科生将参与这个项目，并由个人投资促进机构指导。来自当地专科学校的学生将参加暑期实地考察。PI将参加针对学校教师的Quest暑期计划。

Intellectual merit: N2 fixation is effected exclusively by bacteria and archea using the enzyme nitrogenase, which contains Fe and Mo as metal cofactors in its most active form, and Fe and V, or Fe-only in its alternative forms. The aim of this project is to elucidate how the mechanisms and kinetics of bacterial acquisition of Fe, Mo and V from soils may limit or control N2 fixation rates. N2-fixing bacteria produce siderophores (or ?iron carriers?) to bind iron in the external medium and take up the resulting Fe-siderophore complexes. Our recent work has shown that the siderophores are actually ?metallophores? used in the uptake of Mo and V, along with Fe. The biological acquisition of the various nitrogenase metal cofactors thus depends on their binding by bacterial metallophores. This project is organized around two major hypotheses: 1. Free-living N2-fixing bacteria excrete metallophores that are particularly efficient at capturing the metal (Mo, V or Fe) that is limiting N2 fixation; 2. Because of both competition with other metals for metallophore binding and scarcity in soils, Mo is inherently difficult to acquire and free-living N2-fixing bacteria often use alternative nitrogenases, particularly the V-nitrogenase, to fix N2. These hypotheses will be tested through a combination of laboratory and field experiments. Field studies will focus on sites where Mo may be limiting and employ molecular biological techniques to identify alternative nitrogenases.Broader Impacts: One postdoctoral researcher, one graduate student and several undergraduates will work on this project and be mentored by the PIs. Students from the local junior colleges will participate in the summer field research. The PIs will participate in the Quest summer program for school teachers.