Regulation of metal uptake by TonB-dependent outer membrane transporters of the filamentous cyanobacterium Anabaena sp. PCC 7120

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Cyanobacteria are majorly dependent on metals. The demand for metals like iron for photosynthesis and nitrogen fixation represents a challenge for cyanobacteria, as iron is, on the one hand, not readily bioavailable and, on the other hand, dangerous due to the iron-catalyzed formation of toxic reactiveoxygen species. Cyanobacteria have developed a regulatory network controlling the iron uptake to overcome this dilemma. In Anabaena sp. PCC 7120, a filamentous cyanobacterial model system, 22 TonB-dependent outer membrane transporters and four TonB proteins have been identified. In addition, three ExB and five plasma membrane localized transport systems are encoded by the genome of Anabaena. Our results clearly demonstrate specific expression profiles for the different genes under various conditions. In addition, we have described the complex system for the schizokinen-dependent iron uptake. The next step is to study the regulatory network for metal uptake in general to understand the metal homeostasis in Anabaena sp. PCC 7120 and the regulatory function of outer membrane proteins in this pathway. This will include the description of the function of the TonB-dependent outer membrane transporters as well as the description of the functional and regulatory diversity of the TonB proteins and ExB systems.