蓝细菌（又称蓝藻）是一类原核的光合放氧生物，对全球初级生产力具有重要贡献。作为光合生物，蓝细菌具有很高的铁需求，却广泛分布于缺铁的海洋和淡水环境中，其高效的铁吸收机制备受人们关注。申请人前期研究发现，模式蓝细菌--集胞藻PCC6803利用不同于其它革兰氏阴性菌的TonB-ExbB-ExbD系统（主要负责有机螯合铁的吸收），高效吸收水体中浓度很低的无机自由铁，这很可能是其适应缺铁环境的重要机制。目前该系统中仅ExbB-ExbD已被鉴定，TonB蛋白、外膜受体蛋白及其高效转运无机自由铁的分子机制有待深入研究。本项目拟在前期基础上，通过基因敲除与互补、蛋白定位与相互作用、蛋白结构解析、微量元素洁净分析技术及同位素示踪等手段，鉴定集胞藻PCC6803中的TonB及外膜受体蛋白，阐明其高效结合无机自由铁的结构特征和分子机制，旨在从基础研究的角度揭示蓝细菌特殊的铁吸收机制。

Cyanobacteria are a group of prokaryotic organisms which perform oxygen-evolution photosynthesis. They are globally important primary producers and have high iron requirement, but in which way they dominate in iron-limiting oceans is poorly understood. Our recent studies found that ExbB-ExbD complexes play essential roles in the uptake of inorganic, free iron in cyanobacterium Synechocystis sp. PCC 6803. TonB-ExbB-ExbD system has been investigated for many years in non-photosynthetic bacteria, but its substrates are exclusively organic compounds. Here we show that cyanobacteria utilize this system to take up soluble inorganic iron species, which is probably an important strategy for cyanobacteria to acclimate to iron-limiting oceans. However, TonBs, outer membrane receptors, and molecular mechanisms of free iron uptake are still unclear. Hence, this project plans to identify TonB proteins and its outer membrane receptors in Synechocystis sp. PCC 6803 and to illuminate their iron-uptake molecular mechanisms by the methods of gene knockout and complementation, protein location and protein-protein interaction, protein structural analysis, trace metal clean technique, and isotopic tracer method, etc.. Finally, the information derived from these studies will illustrate a working model of the special iron uptake pathway in cyanobacteria.