title: Long helical filaments are not seen encircling cells in electron cryotomograms of rod-shaped bacteria.
abstract: How rod-shaped bacteria form and maintain their shape is an important question in bacterial cell biology. Results from fluorescent light microscopy have led many to believe that the actin homolog MreB and a number of other proteins form long helical filaments along the inner membrane of the cell. Here we show using electron cryotomography of six different rod-shaped bacterial species, at macromolecular resolution, that no long (> 80 nm) helical filaments exist near or along either surface of the inner membrane. We also use correlated cryo-fluorescent light microscopy (cryo-fLM) and electron cryo-tomography (ECT) to identify cytoplasmic bundles of MreB, showing that MreB filaments are detectable by ECT. In light of these results, the structure and function of MreB must be reconsidered: instead of acting as a large, rigid scaffold that localizes cell-wall synthetic machinery, moving MreB complexes may apply tension to growing peptidoglycan strands to ensure their orderly, linear insertion.
authors.affiliation: Division of Biology, California Institute of Technology, 1200 E California Blvd., Pasadena, CA 91125, United States.
authors.forename: Matthew T
authors.initials: MT
authors.lastname: Swulius
authors.forename: Songye
authors.initials: S
authors.lastname: Chen
authors.forename: H
authors.initials: H
authors.lastname: Jane Ding
authors.forename: Zhuo
authors.initials: Z
authors.lastname: Li
authors.forename: Ariane
authors.initials: A
authors.lastname: Briegel
authors.forename: Martin
authors.initials: M
authors.lastname: Pilhofer
authors.forename: Elitza I
authors.initials: EI
authors.lastname: Tocheva
authors.forename: Suzanne R
authors.initials: SR
authors.lastname: Lybarger
authors.forename: Tanya L
authors.initials: TL
authors.lastname: Johnson
authors.forename: Maria
authors.initials: M
authors.lastname: Sandkvist
authors.forename: Grant J
authors.initials: GJ
authors.lastname: Jensen
mesh_terms: D001412:Bacillus subtilis / Q000378:metabolism / Q000648:ultrastructure; D001419:Bacteria / Q000378:metabolism* / Q000648:ultrastructure*; D025065:Borrelia burgdorferi / Q000378:metabolism / Q000648:ultrastructure; D016935:Caulobacter crescentus / Q000378:metabolism / Q000648:ultrastructure; D020285:Cryoelectron Microscopy; D003599:Cytoskeleton / Q000648:ultrastructure*; D004926:Escherichia coli / Q000378:metabolism / Q000648:ultrastructure; D029968:Escherichia coli Proteins / Q000032:analysis / Q000378:metabolism*; D014734:Vibrio cholerae / Q000378:metabolism / Q000648:ultrastructure
chemical_list: D029968:Escherichia coli Proteins; C078473:MreB protein, E coli