Intercellular Diffusion of a Fluorescent Sucrose Analog via the Septal Junctions in a Filamentous Cyanobacterium

ABSTRACT Many filamentous cyanobacteria produce specialized nitrogen-fixing cells called heterocysts, which are located at semiregular intervals along the filament with about 10 to 20 photosynthetic vegetative cells in between. Nitrogen fixation in these complex multicellular bacteria depends on met...

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Autores principales:	Dennis J. Nürnberg, Vicente Mariscal, Jan Bornikoel, Mercedes Nieves-Morión, Norbert Krauß, Antonia Herrero, Iris Maldener, Enrique Flores, Conrad W. Mullineaux
Formato:	article
Lenguaje:	EN
Publicado:	American Society for Microbiology 2015
Materias:	Microbiology QR1-502
Acceso en línea:	https://doaj.org/article/c4a2078e9bfc44de9411bd2b26fa17b1
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spelling	oai:doaj.org-article:c4a2078e9bfc44de9411bd2b26fa17b12021-11-15T15:41:34ZIntercellular Diffusion of a Fluorescent Sucrose Analog via the Septal Junctions in a Filamentous Cyanobacterium10.1128/mBio.02109-142150-7511https://doaj.org/article/c4a2078e9bfc44de9411bd2b26fa17b12015-05-01T00:00:00Zhttps://journals.asm.org/doi/10.1128/mBio.02109-14https://doaj.org/toc/2150-7511ABSTRACT Many filamentous cyanobacteria produce specialized nitrogen-fixing cells called heterocysts, which are located at semiregular intervals along the filament with about 10 to 20 photosynthetic vegetative cells in between. Nitrogen fixation in these complex multicellular bacteria depends on metabolite exchange between the two cell types, with the heterocysts supplying combined-nitrogen compounds but dependent on the vegetative cells for photosynthetically produced carbon compounds. Here, we used a fluorescent tracer to probe intercellular metabolite exchange in the filamentous heterocyst-forming cyanobacterium Anabaena sp. strain PCC 7120. We show that esculin, a fluorescent sucrose analog, is incorporated by a sucrose import system into the cytoplasm of Anabaena cells. The cytoplasmic esculin is rapidly and reversibly exchanged across vegetative-vegetative and vegetative-heterocyst cell junctions. Our measurements reveal the kinetics of esculin exchange and also show that intercellular metabolic communication is lost in a significant fraction of older heterocysts. SepJ, FraC, and FraD are proteins located at the intercellular septa and are suggested to form structures analogous to gap junctions. We show that a ΔsepJ ΔfraC ΔfraD triple mutant shows an altered septum structure with thinner septa but a denser peptidoglycan layer. Intercellular diffusion of esculin and fluorescein derivatives is impaired in this mutant, which also shows a greatly reduced frequency of nanopores in the intercellular septal cross walls. These findings suggest that FraC, FraD, and SepJ are important for the formation of junctional structures that constitute the major pathway for feeding heterocysts with sucrose. IMPORTANCE Anabaena and its relatives are filamentous cyanobacteria that exhibit a sophisticated form of prokaryotic multicellularity, with the formation of differentiated cell types, including normal photosynthetic cells and specialized nitrogen-fixing cells called heterocysts. The question of how heterocysts communicate and exchange metabolites with other cells in the filament is key to understanding this form of bacterial multicellularity. Here we provide the first information on the intercellular exchange of a physiologically important molecule, sucrose. We show that a fluorescent sucrose analog can be imported into the Anabaena cytoplasm by a sucrose import system. Once in the cytoplasm, it is rapidly and reversibly exchanged among all of the cells in the filament by diffusion across the septal junctions. Photosynthetically produced sucrose likely follows the same route from cytoplasm to cytoplasm. We identify some of the septal proteins involved in sucrose exchange, and our results indicate that these proteins form structures functionally analogous to metazoan gap junctions.Dennis J. NürnbergVicente MariscalJan BornikoelMercedes Nieves-MoriónNorbert KraußAntonia HerreroIris MaldenerEnrique FloresConrad W. MullineauxAmerican Society for MicrobiologyarticleMicrobiologyQR1-502ENmBio, Vol 6, Iss 2 (2015)
institution	DOAJ
collection	DOAJ
language	EN
topic	Microbiology QR1-502
spellingShingle	Microbiology QR1-502 Dennis J. Nürnberg Vicente Mariscal Jan Bornikoel Mercedes Nieves-Morión Norbert Krauß Antonia Herrero Iris Maldener Enrique Flores Conrad W. Mullineaux Intercellular Diffusion of a Fluorescent Sucrose Analog via the Septal Junctions in a Filamentous Cyanobacterium
description	ABSTRACT Many filamentous cyanobacteria produce specialized nitrogen-fixing cells called heterocysts, which are located at semiregular intervals along the filament with about 10 to 20 photosynthetic vegetative cells in between. Nitrogen fixation in these complex multicellular bacteria depends on metabolite exchange between the two cell types, with the heterocysts supplying combined-nitrogen compounds but dependent on the vegetative cells for photosynthetically produced carbon compounds. Here, we used a fluorescent tracer to probe intercellular metabolite exchange in the filamentous heterocyst-forming cyanobacterium Anabaena sp. strain PCC 7120. We show that esculin, a fluorescent sucrose analog, is incorporated by a sucrose import system into the cytoplasm of Anabaena cells. The cytoplasmic esculin is rapidly and reversibly exchanged across vegetative-vegetative and vegetative-heterocyst cell junctions. Our measurements reveal the kinetics of esculin exchange and also show that intercellular metabolic communication is lost in a significant fraction of older heterocysts. SepJ, FraC, and FraD are proteins located at the intercellular septa and are suggested to form structures analogous to gap junctions. We show that a ΔsepJ ΔfraC ΔfraD triple mutant shows an altered septum structure with thinner septa but a denser peptidoglycan layer. Intercellular diffusion of esculin and fluorescein derivatives is impaired in this mutant, which also shows a greatly reduced frequency of nanopores in the intercellular septal cross walls. These findings suggest that FraC, FraD, and SepJ are important for the formation of junctional structures that constitute the major pathway for feeding heterocysts with sucrose. IMPORTANCE Anabaena and its relatives are filamentous cyanobacteria that exhibit a sophisticated form of prokaryotic multicellularity, with the formation of differentiated cell types, including normal photosynthetic cells and specialized nitrogen-fixing cells called heterocysts. The question of how heterocysts communicate and exchange metabolites with other cells in the filament is key to understanding this form of bacterial multicellularity. Here we provide the first information on the intercellular exchange of a physiologically important molecule, sucrose. We show that a fluorescent sucrose analog can be imported into the Anabaena cytoplasm by a sucrose import system. Once in the cytoplasm, it is rapidly and reversibly exchanged among all of the cells in the filament by diffusion across the septal junctions. Photosynthetically produced sucrose likely follows the same route from cytoplasm to cytoplasm. We identify some of the septal proteins involved in sucrose exchange, and our results indicate that these proteins form structures functionally analogous to metazoan gap junctions.
format	article
author	Dennis J. Nürnberg Vicente Mariscal Jan Bornikoel Mercedes Nieves-Morión Norbert Krauß Antonia Herrero Iris Maldener Enrique Flores Conrad W. Mullineaux
author_facet	Dennis J. Nürnberg Vicente Mariscal Jan Bornikoel Mercedes Nieves-Morión Norbert Krauß Antonia Herrero Iris Maldener Enrique Flores Conrad W. Mullineaux
author_sort	Dennis J. Nürnberg
title	Intercellular Diffusion of a Fluorescent Sucrose Analog via the Septal Junctions in a Filamentous Cyanobacterium
title_short	Intercellular Diffusion of a Fluorescent Sucrose Analog via the Septal Junctions in a Filamentous Cyanobacterium
title_full	Intercellular Diffusion of a Fluorescent Sucrose Analog via the Septal Junctions in a Filamentous Cyanobacterium
title_fullStr	Intercellular Diffusion of a Fluorescent Sucrose Analog via the Septal Junctions in a Filamentous Cyanobacterium
title_full_unstemmed	Intercellular Diffusion of a Fluorescent Sucrose Analog via the Septal Junctions in a Filamentous Cyanobacterium
title_sort	intercellular diffusion of a fluorescent sucrose analog via the septal junctions in a filamentous cyanobacterium
publisher	American Society for Microbiology
publishDate	2015
url	https://doaj.org/article/c4a2078e9bfc44de9411bd2b26fa17b1
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Intercellular Diffusion of a Fluorescent Sucrose Analog via the Septal Junctions in a Filamentous Cyanobacterium

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