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

智力优点：固氮作用仅由细菌和古细菌使用固氮酶来实现，固氮酶以其最活跃的形式含有作为金属辅因子的Fe和Mo，以及以其替代形式的Fe和V或仅Fe。本项目的目的是阐明如何从土壤中的铁，钼和V的细菌收购的机制和动力学可能会限制或控制固氮率。固氮细菌产生铁载体（或？铁载体？）结合外部介质中的铁并吸收所得的Fe-铁载体复合物。我们最近的研究表明铁载体实际上是？金属载体？用于Mo和V的吸收，沿着Fe。因此，各种固氮酶金属辅因子的生物获得取决于它们与细菌金属载体的结合。这个项目是围绕两个主要假设：1。自由生活的N2固定细菌分泌金属载体，其在捕获限制N2固定的金属（Mo、V或Fe）方面特别有效; 2.由于与其他金属竞争金属结合和土壤中的稀缺性，Mo本质上很难获得，并且自由生活的固氮细菌通常使用替代固氮酶，特别是V-固氮酶来固定N2。这些假设将通过实验室和实地实验相结合的方式进行检验。实地研究将集中在钼可能限制的地点，并采用分子生物学技术来确定替代固氮酶。更广泛的影响：一名博士后研究员，一名研究生和几名本科生将在这个项目上工作，并由PI指导。当地大专院校的学生将参加夏季实地考察。PI将参加学校教师的探索夏季计划。

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.