title: Chromatin organization and radio resistance in the bacterium Gemmata obscuriglobus.
abstract: The organization of chromatin has a major impact on cellular activities, such as gene expression. For bacteria, it was suggested that the spatial organization of the genetic material correlates with transcriptional levels, implying a specific architecture of the chromosome within the cytoplasm. Accordingly, recent technological advances have emphasized the organization of the genetic material within nucleoid structures. Gemmata obscuriglobus, a member of the phylum Planctomycetes, exhibits a distinctive nucleoid structure in which chromatin is encapsulated within a discrete membrane-bound compartment. Here, we show that this soil and freshwater bacterium tolerates high doses of UV and ionizing radiation. Cryoelectron tomography of frozen hydrated sections and electron microscopy of freeze-substituted cells have indicated a more highly ordered condensed-chromatin organization in actively dividing and stationary-phase G. obscuriglobus cells. These three-dimensional analyses revealed a complex network of double membranes that engulf the condensed DNA. Bioinformatics analysis has revealed the existence of a putative component involved in nonhomologous DNA end joining that presumably plays a role in maintaining chromatin integrity within the bacterium. Thus, our observations further support the notion that packed chromatin organization enhances radiation tolerance.
authors.affiliation: Department of Life Sciences, Ben-Gurion University of the Negev, Israel.
authors.forename: Arnon
authors.initials: A
authors.lastname: Lieber
authors.forename: Andrew
authors.initials: A
authors.lastname: Leis
authors.forename: Ariel
authors.initials: A
authors.lastname: Kushmaro
authors.forename: Abraham
authors.initials: A
authors.lastname: Minsky
authors.forename: Ohad
authors.initials: O
authors.lastname: Medalia
mesh_terms: D001419:Bacteria / Q000254:growth & development / Q000302:isolation & purification / Q000528:radiation effects* / Q000648:ultrastructure; D002843:Chromatin / Q000737:chemistry* / Q000648:ultrastructure*; D004269:DNA, Bacterial / Q000235:genetics; D005618:Fresh Water / Q000382:microbiology; D008854:Microscopy, Electron; D011836:Radiation Tolerance; D011839:Radiation, Ionizing; D012988:Soil Microbiology; D014054:Tomography; D014466:Ultraviolet Rays
chemical_list: D002843:Chromatin; D004269:DNA, Bacterial