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Applied and Environmental Microbiology, September 2005, p. 5225-5235, Vol. 71, No. 9
0099-2240/05/$08.00+0     doi:10.1128/AEM.71.9.5225-5235.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Extensive Diversity of Ionizing-Radiation-Resistant Bacteria Recovered from Sonoran Desert Soil and Description of Nine New Species of the Genus Deinococcus Obtained from a Single Soil Sample{dagger}

Fred A. Rainey,1* Keren Ray,1 Margarida Ferreira,2 Bridget Z. Gatz,1 M. Fernanda Nobre,3 Danielle Bagaley,1 Brian A. Rash,1 Mie-Jung Park,1 Ashlee M. Earl,1 Nicole C. Shank,1 Alanna M. Small,1 Margaret C. Henk,1 John R. Battista,1 Peter Kämpfer,4 and Milton S. da Costa2

Department of Biological Sciences, Louisiana State University, Baton Rouge, Louisiana 70803,1 Departamento de Bioquímica and Centro de Neurociências e Biologia Celular,2 Departamento de Zoologia, Universidade de Coimbra, 3004-517 Coimbra, Portugal,3 Institut für Angewandte Mikrobiologie, Justus-Liebig-Universität Giessen, D-35392 Giessen, Germany4

Received 17 August 2004/ Accepted 18 March 2005

The ionizing-radiation-resistant fractions of two soil bacterial communities were investigated by exposing an arid soil from the Sonoran Desert and a nonarid soil from a Louisiana forest to various doses of ionizing radiation using a 60Co source. The numbers of surviving bacteria decreased as the dose of gamma radiation to which the soils were exposed increased. Bacterial isolates surviving doses of 30 kGy were recovered from the Sonoran Desert soil, while no isolates were recovered from the nonarid forest soil after exposure to doses greater than 13 kGy. The phylogenetic diversities of the surviving culturable bacteria were compared for the two soils using 16S rRNA gene sequence analysis. In addition to a bacterial population that was more resistant to higher doses of ionizing radiation, the diversity of the isolates was greater in the arid soil. The taxonomic diversity of the isolates recovered was found to decrease as the level of ionizing-radiation exposure increased. Bacterial isolates of the genera Deinococcus, Geodermatophilus, and Hymenobacter were still recovered from the arid soil after exposure to doses of 17 to 30 kGy. The recovery of large numbers of extremely ionizing-radiation-resistant bacteria from an arid soil and not from a nonarid soil provides further ecological support for the hypothesis that the ionizing-radiation resistance phenotype is a consequence of the evolution of other DNA repair systems that protect cells against commonly encountered environmental stressors, such as desiccation. The diverse group of bacterial strains isolated from the arid soil sample included 60 Deinococcus strains, the characterization of which revealed nine novel species of this genus.

* Corresponding author. Mailing address: Department of Biological Sciences, 202 Life Sciences Building, Louisiana State University, Baton Rouge, LA 70803. Phone: (225) 578-8859. Fax: (225) 578-8826. E-mail: frainey{at}lsu.edu.

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

Applied and Environmental Microbiology, September 2005, p. 5225-5235, Vol. 71, No. 9
0099-2240/05/$08.00+0     doi:10.1128/AEM.71.9.5225-5235.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.



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