title: Crystal habits and magnetic microstructures of magnetosomes in coccoid magnetotactic bacteria.
abstract: We report on the application of off-axis electron holography and high-resolution TEM to study the crystal habits of magnetosomes and magnetic microstructure in two coccoid morphotypes of magnetotactic bacteria collected from a brackish lagoon at Itaipu, Brazil. Itaipu-1, the larger coccoid organism, contains two separated chains of unusually large magnetosomes; the magnetosome crystals have roughly square projections, lengths up to 250 nm and are slightly elongated along [111] (width/length ratio of about 0.9). Itaipu-3 magnetosome crystals have lengths up to 120 nm, greater elongation along [111] (width/length approximately 0.6), and prominent corner facets. The results show that Itaipu-1 and Itaipu-3 magnetosome crystal habits are related, differing only in the relative sizes of their crystal facets. In both cases, the crystals are aligned with their [111] elongation axes parallel to the chain direction. In Itaipu-1, but not Itaipu-3, crystallographic positioning perpendicular to [111] of successive crystals in the magnetosome chain appears to be under biological control. Whereas the large magnetosomes in Itaipu-1 are metastable, single-magnetic domains, magnetosomes in Itaipu-3 are permanent, single-magnetic domains, as in most magnetotactic bacteria.
authors.affiliation: Instituto de Microbiologia Professor Paulo de Góes, CCS, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ, Brasil. ulins@micro.ufrj.br
authors.forename: Ulysses
authors.initials: U
authors.lastname: Lins
authors.forename: Martha R
authors.initials: MR
authors.lastname: McCartney
authors.forename: Marcos
authors.initials: M
authors.lastname: Farina
authors.forename: Richard B
authors.initials: RB
authors.lastname: Frankel
authors.forename: Peter R
authors.initials: PR
authors.lastname: Buseck
mesh_terms: D001419:Bacteria / Q000737:chemistry / Q000648:ultrastructure*; D003460:Crystallization; D006696:Holography; D008280:Magnetics; D046529:Microscopy, Electron, Transmission