title: Ultrastructure and cytochemistry of lipid granules in the many-celled magnetotactic prokaryote, 'Candidatus Magnetoglobus multicellularis'.
abstract: Conspicuous cytoplasmic granules are reported in a magnetotactic multicellular prokaryote named 'Candidatus Magnetoglobus multicellularis'. Unfortunately, this microorganism, which consists of an assembly of gram-negative bacterial cells, cannot yet be cultivated, limiting the biochemical analysis of the granules and preventing in vitro studies with starvation/excess of nutrients. In this scenario, light and electron microscopy techniques were used to partially address the nature of the granules. Besides magnetosomes, three types of inclusions were observed: small (mean diameter=124 nm) polyhydroxyalkanoate-like (PHA) granules, large (diameters ranging from 0.11 to 2.5 microm) non-PHA lipid granules, and rare phosphorus-rich granules, which probably correspond to polyphosphate bodies. The PHA granules were rounded in projection, non-reactive with OsO(4), and suffered the typical plastic deformation of PHAs after freeze fracturing. The nature of the large granules, consisting of round globular structures (mean diameter=0.76 microm), was classified as non-PHA based on the following data: (a) multilayered structure in freeze-fracture electron microscopy, typical of non-PHA lipids; (b) Nile blue fluorescence imaging detected non-PHA lipids; (c) imidazole buffered osmium tetroxide and ruthenium red cytochemistry stained the globules, which appeared as electron-dense granules instead of electron lucent as PHAs do. Most likely, 'Candidatus Magnetoglobus multicellularis' stores carbon mainly as unusual lipid granules, together with smaller amounts of PHAs.
authors.affiliation: Instituto de Microbiologia Professor Paulo de Góes, Universidade Federal do Rio de Janeiro, 21941-590 Rio de Janeiro, RJ, Brazil.
authors.forename: Karen Tavares
authors.initials: KT
authors.lastname: Silva
authors.forename: Fernanda
authors.initials: F
authors.lastname: Abreu
authors.forename: Carolina N
authors.initials: CN
authors.lastname: Keim
authors.forename: Marcos
authors.initials: M
authors.lastname: Farina
authors.forename: Ulysses
authors.initials: U
authors.lastname: Lins
mesh_terms: D003594:Cytoplasmic Granules / Q000648:ultrastructure*; D004577:Electron Probe Microanalysis; D005614:Freeze Fracturing; D006090:Gram-Negative Bacteria / Q000737:chemistry / Q000648:ultrastructure*; D008055:Lipids / Q000032:analysis*; D008280:Magnetics; D046529:Microscopy, Electron, Transmission; D054813:Polyhydroxyalkanoates / Q000032:analysis
chemical_list: D008055:Lipids; D054813:Polyhydroxyalkanoates