title: Envelope ultrastructure of uncultured naturally occurring magnetotactic cocci.
abstract: Magnetotactic bacteria are microorganisms that respond to magnetic fields. We studied the surface ultrastructure of uncultured magnetotactic cocci collected from a marine environment by transmission electron microscopy using freeze-fracture and freeze-etching. All bacteria revealed a Gram-negative cell wall. Many bacteria possessed extensive capsular material and a S-layer formed by particles arranged with hexagonal symmetry. No indication of a metal precipitation on the surface of these microorganisms was observed. Numerous membrane vesicles were observed on the surface of the bacteria. Flagella were organized in bundles originated in a depression on the surface of the cells. Occasionally, a close association of the flagella with the magnetosomes that remained attached to the replica was observed. Capsules and S-layers are common structures in magnetotactic cocci from natural sediments and may be involved in inhibition of metal precipitation on the cell surface or indirectly influence magnetotaxis.
authors.affiliation: Departamento de Microbiologia Geral, Instituto de Microbiologia Prof. Paulo de Góes, Universidade Federal do Rio de Janeiro, CCS, Bloco I, 21941-590, RJ, Rio de Janeiro, Brazil.
authors.forename: Flávia
authors.initials: F
authors.lastname: Freitas
authors.forename: Carolina N
authors.initials: CN
authors.lastname: Keim
authors.forename: Bechara
authors.initials: B
authors.lastname: Kachar
authors.forename: Marcos
authors.initials: M
authors.lastname: Farina
authors.forename: Ulysses
authors.initials: U
authors.lastname: Lins
mesh_terms: D002462:Cell Membrane / Q000648:ultrastructure; D002473:Cell Wall / Q000648:ultrastructure*; D005407:Flagella / Q000648:ultrastructure; D005613:Freeze Etching; D005614:Freeze Fracturing; D006090:Gram-Negative Bacteria / Q000254:growth & development / Q000502:physiology / Q000648:ultrastructure*; D008280:Magnetics; D008854:Microscopy, Electron; D015388:Organelles / Q000648:ultrastructure; D012623:Seawater / Q000382:microbiology*