title: FraH is required for reorganization of intracellular membranes during heterocyst differentiation in Anabaena sp. strain PCC 7120.
abstract: In the filamentous, heterocyst-forming cyanobacteria, two different cell types, the CO(2)-fixing vegetative cells and the N(2)-fixing heterocysts, exchange nutrients and regulators for diazotrophic growth. In the model organism Anabaena sp. strain PCC 7120, inactivation of fraH produces filament fragmentation under conditions of combined nitrogen deprivation, releasing numerous isolated heterocysts. Transmission electron microscopy of samples prepared by either high-pressure cryo-fixation or chemical fixation showed that the heterocysts of a ΔfraH mutant lack the intracellular membrane system structured close to the heterocyst poles, known as the honeycomb, that is characteristic of wild-type heterocysts. Using a green fluorescent protein translational fusion to the carboxyl terminus of FraH (FraH-C-GFP), confocal microscopy showed spots of fluorescence located at the periphery of the vegetative cells in filaments grown in the presence of nitrate. After incubation in the absence of combined nitrogen, localization of FraH-C-GFP changed substantially, and the GFP fluorescence was conspicuously located at the cell poles in the heterocysts. Fluorescence microscopy and deconvolution of images showed that GFP fluorescence originated mainly from the region next to the cyanophycin plug present at the heterocyst poles. Intercellular transfer of the fluorescent tracers calcein (622 Da) and 5-carboxyfluorescein (374 Da) was either not impaired or only partially impaired in the ΔfraH mutant, suggesting that FraH is not important for intercellular molecular exchange. Location of FraH close to the honeycomb membrane structure and lack of such structure in the ΔfraH mutant suggest a role of FraH in reorganization of intracellular membranes, which may involve generation of new membranes, during heterocyst differentiation.
authors.affiliation: Instituto de Bioquímica Vegetal y Fotosíntesis, Consejo Superior de Investigaciones Científicas and Universidad de Sevilla, Seville, Spain.
authors.forename: Victoria
authors.initials: V
authors.lastname: Merino-Puerto
authors.forename: Vicente
authors.initials: V
authors.lastname: Mariscal
authors.forename: Heinz
authors.initials: H
authors.lastname: Schwarz
authors.forename: Iris
authors.initials: I
authors.lastname: Maldener
authors.forename: Conrad W
authors.initials: CW
authors.lastname: Mullineaux
authors.forename: Antonia
authors.initials: A
authors.lastname: Herrero
authors.forename: Enrique
authors.initials: E
authors.lastname: Flores
mesh_terms: D017033:Anabaena / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D007425:Intracellular Membranes / Q000378:metabolism*; D009154:Mutation; D021381:Protein Transport
chemical_list: D001426:Bacterial Proteins; D049452:Green Fluorescent Proteins