title: Existence of periplasmic barriers preventing green fluorescent protein diffusion from cell to cell in the cyanobacterium Anabaena sp. strain PCC 7120.
abstract: When deprived of combined nitrogen, the filamentous cyanobacterium Anabaena PCC 7120 relies on intercellular cooperation involving two cell types: nitrogen-fixing heterocysts and photosynthetic vegetative cells. Heterocysts send fixed nitrogen to vegetative cells over long distances along the filament, receiving a reduced carbon source from them. These intercellular exchanges might involve a continuous periplasm along the filament or cytoplasm-to-cytoplasm conduits or both. In the present study, the green fluorescent protein (GFP) was fused to a twin-arginine translocation signal sequence, which exported GFP to the periplasm of either a heterocyst using the heterocyst-specific promoters PhepA and PpatB or to the periplasm of vegetative cells using the vegetative cell-specific promoter PrbcL. Using the techniques of FRAP (fluorescence recovery after photobleaching) and FLIP (fluorescence loss in photobleaching), we found no evidence for intercellular diffusion of GFP through the periplasm, either from a heterocyst to vegetative cells or vice versa, or among vegetative cells. GFP could diffuse within the periplasm of the producing cell, but the diffusion stopped at the cell border. GFP diffusion could occur between two dividing cells before septum closure. This study indicates that barriers exist at the periplasmic space to prevent free GFP diffusion across cell border along the filament.
authors.affiliation: State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan 430070, China.
authors.forename: Li-Chen
authors.initials: LC
authors.lastname: Zhang
authors.forename: Yi-Fei
authors.initials: YF
authors.lastname: Chen
authors.forename: Wen-Li
authors.initials: WL
authors.lastname: Chen
authors.forename: Cheng-Cai
authors.initials: CC
authors.lastname: Zhang
mesh_terms: D017033:Anabaena / Q000166:cytology / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D001692:Biological Transport; D002450:Cell Communication; D004058:Diffusion; D036681:Fluorescence Recovery After Photobleaching; D015964:Gene Expression Regulation, Bacterial; D017930:Genes, Reporter; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism*; D008856:Microscopy, Fluorescence; D019897:Periplasm / Q000378:metabolism*; D038761:Photobleaching; D011401:Promoter Regions, Genetic; D021382:Protein Sorting Signals; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D021382:Protein Sorting Signals; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins