title: Mechanism of intercellular molecular exchange in heterocyst-forming cyanobacteria.
abstract: Heterocyst-forming filamentous cyanobacteria are true multicellular prokaryotes, in which heterocysts and vegetative cells have complementary metabolism and are mutually dependent. The mechanism for metabolite exchange between cells has remained unclear. To gain insight into the mechanism and kinetics of metabolite exchange, we introduced calcein, a 623-Da fluorophore, into the Anabaena cytoplasm. We used fluorescence recovery after photobleaching to quantify rapid diffusion of this molecule between the cytoplasms of all the cells in the filament. This indicates nonspecific intercellular channels allowing the movement of molecules from cytoplasm to cytoplasm. We quantify rates of molecular exchange as filaments adapt to diazotrophic growth. Exchange among vegetative cells becomes faster as filaments differentiate, becoming considerably faster than exchange with heterocysts. Slower exchange is probably a price paid to maintain a microaerobic environment in the heterocyst. We show that the slower exchange is partly due to the presence of cyanophycin polar nodules in heterocysts. The phenotype of a null mutant identifies FraG (SepJ), a membrane protein localised at the cell-cell interface, as a strong candidate for the channel-forming protein.
authors.affiliation: School of Biological and Chemical Sciences, Queen Mary, University of London, London, UK. c.mullineaux@qmul.ac.uk
authors.forename: Conrad W
authors.initials: CW
authors.lastname: Mullineaux
authors.forename: Vicente
authors.initials: V
authors.lastname: Mariscal
authors.forename: Anja
authors.initials: A
authors.lastname: Nenninger
authors.forename: Hajara
authors.initials: H
authors.lastname: Khanum
authors.forename: Antonia
authors.initials: A
authors.lastname: Herrero
authors.forename: Enrique
authors.initials: E
authors.lastname: Flores
authors.forename: David G
authors.initials: DG
authors.lastname: Adams
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D001692:Biological Transport; D000458:Cyanobacteria / Q000166:cytology* / Q000235:genetics / Q000378:metabolism*; D005452:Fluoresceins / Q000378:metabolism; D036681:Fluorescence Recovery After Photobleaching; D005456:Fluorescent Dyes / Q000378:metabolism; D018613:Microscopy, Confocal
chemical_list: D001426:Bacterial Proteins; D005452:Fluoresceins; D005456:Fluorescent Dyes; C007740:fluorexon