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Journal of Bacteriology, March 2009, p. 1439-1445, Vol. 191, No. 5
0021-9193/09/$08.00+0     doi:10.1128/JB.01513-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Chromatin Organization and Radio Resistance in the Bacterium Gemmata obscuriglobus{triangledown} ,{dagger}

Arnon Lieber,1 Andrew Leis,2 Ariel Kushmaro,3,5 Abraham Minsky,4 and Ohad Medalia1,5*

Department of Life Sciences, Ben-Gurion University of the Negev, Beer Sheva 84105, Israel,1 Max Planck Institute for Biochemistry, 82152 Martinsried, Germany,2 Department of Biotechnology Engineering, Ben-Gurion University of the Negev, Beer Sheva 84120, Israel,3 Department of Organic Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel,4 The National Institute of Biotechnology in the Negev, Ben-Gurion University of the Negev, Beer Sheva 84105, Israel5

Received 26 October 2008/ Accepted 7 December 2008

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.

* Corresponding author. Mailing address: Department of Life Sciences, Ben-Gurion University of the Negev, Beer Sheva 84105, Israel. Phone: 972-8-6479236. Fax: 972-8-6472657. E-mail: omedalia{at}bgu.ac.il

{triangledown} Published ahead of print on 12 December 2008.

{dagger} Supplemental material for this article may be found at http://jb.asm.org/.

Journal of Bacteriology, March 2009, p. 1439-1445, Vol. 191, No. 5
0021-9193/09/$08.00+0     doi:10.1128/JB.01513-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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