title: Membrane invagination in Rhodobacter sphaeroides is initiated at curved regions of the cytoplasmic membrane, then forms both budded and fully detached spherical vesicles.
abstract: The purple phototrophic bacteria synthesize an extensive system of intracytoplasmic membranes (ICM) in order to increase the surface area for absorbing and utilizing solar energy. Rhodobacter sphaeroides cells contain curved membrane invaginations. In order to study the biogenesis of ICM in this bacterium mature (ICM) and precursor (upper pigmented band - UPB) membranes were purified and compared at the single membrane level using electron, atomic force and fluorescence microscopy, revealing fundamental differences in their morphology, protein organization and function. Cryo-electron tomography demonstrates the complexity of the ICM of Rba. sphaeroides. Some ICM vesicles have no connection with other structures, others are found nearer to the cytoplasmic membrane (CM), often forming interconnected structures that retain a connection to the CM, and possibly having access to the periplasmic space. Near-spherical single invaginations are also observed, still attached to the CM by a 'neck'. Small indents of the CM are also seen, which are proposed to give rise to the UPB precursor membranes upon cell disruption. 'Free-living' ICM vesicles, which possess all the machinery for converting light energy into ATP, can be regarded as bacterial membrane organelles.
authors.affiliation: Department of Molecular Biology and Biotechnology, University of Sheffield, Western Bank, Firth Court, Sheffield S10 2TN, UK.
authors.forename: Jaimey D
authors.initials: JD
authors.lastname: Tucker
authors.forename: C Alistair
authors.initials: CA
authors.lastname: Siebert
authors.forename: Maryana
authors.initials: M
authors.lastname: Escalante
authors.forename: Peter G
authors.initials: PG
authors.lastname: Adams
authors.forename: John D
authors.initials: JD
authors.lastname: Olsen
authors.forename: Cees
authors.initials: C
authors.lastname: Otto
authors.forename: David L
authors.initials: DL
authors.lastname: Stokes
authors.forename: C Neil
authors.initials: CN
authors.lastname: Hunter
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry; D002462:Cell Membrane / Q000648:ultrastructure*; D020285:Cryoelectron Microscopy; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry; D018625:Microscopy, Atomic Force; D008856:Microscopy, Fluorescence; D012242:Rhodobacter sphaeroides / Q000648:ultrastructure*
chemical_list: C081521:B800-850 light-harvesting complex, bacteria; D001426:Bacterial Proteins; D045342:Light-Harvesting Protein Complexes; C094744:light-harvesting complex 1, Rhodospirillum