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Updated: Apr 6, 2026

Natural Transformation, Protein Expression, and Cryoconservation of the Filamentous Cyanobacterium Phormidium lacuna
Published on: February 1, 2022
Requirement of Fra proteins for communication channels between cells in the filamentous nitrogen-fixing
Amin Omairi-Nasser1, Vicente Mariscal2, Jotham R Austin3
1Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, IL 60637;
Abstract:
The filamentous nitrogen-fixing cyanobacterium Anabaena sp. PCC 7120 differentiates specialized cells, heterocysts, that fix atmospheric nitrogen and transfer the fixed nitrogen to adjacent vegetative cells. Reciprocally, vegetative cells transfer fixed carbon to heterocysts. Several routes have been described for metabolite exchange within the filament, one of which involves communicating channels that penetrate the septum between adjacent cells. Several fra gene mutants were isolated 25 y ago on the basis of their phenotypes: inability to fix nitrogen and fragmentation of filaments upon transfer from N+ to N- media. Cryopreservation combined with electron tomography were used to investigate the role of three fra gene products in channel formation. FraC and FraG are clearly involved in channel formation, whereas FraD has a minor part. Additionally, FraG was located close to the cytoplasmic membrane and in the heterocyst neck, using immunogold labeling with antibody raised to the N-terminal domain of the FraG protein.
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