DNA-Repair Potential of Halomonas spp. from the Salt Plains Microbial Observatory of Oklahoma C. Wilson 1 , T.M. Caton 2 , J.A. Buchheim 3 , M.A. Buchheim 3 , M.A. Schneegurt 2 and R.V. Miller 1 (1) Department of Microbiology and Molecular Genetics, Oklahoma State University, Stillwater, OK 74078, USA (2) Department of Biological Sciences, Wichita State University, Wichita, KS 67260, USA (3) Department of Biological Science, University of Tulsa, Tulsa, OK 74104, USA Received: 31 October 2003 / Accepted: 26 April 2004 / Online publication: 9 November 2004 Abstract The Great Salt Plains (GSP), an unvegetated, barren salt flat that is part of the Salt Plains National Wildlife Refuge near Cherokee, Oklahoma, is the site of the Salt Plains Microbial Observatory. At the GSP the briny remains of an ancient sea rise to the surface, evaporate under dry conditions, and leave crusts of white salt. Adaptation to this environment requires development of coping mechanisms providing tolerance to desiccating condi- tions due to the high salinity, extreme temperatures, alkaline pH, unrelenting exposure to solar UV radiation, and prevailing winds. Several lines of evidence suggest that the same DNA repair mechanisms that are usually associated with UV light or chemically induced DNA damage are also important in protecting microbes from desiccation. Because little is known about the DNA repair capacity of microorganisms from hypersaline terrestrial environments, we explored the DNA repair capacity of microbial isolates from the GSP. We used survival fol- lowing exposure to UV light as a convenient tool to assess DNA repair capacity. Two species of Halomonas (H. salina and H. venusta) that have been isolated repeatedly from the GSP were chosen for analysis. The survival profiles were compared to those of Escherichia coli, Pseudomonas aeruginosa, and Halomonas spp. from aquatic saline environments. Survival of GSP organisms exceeded that of the freshwater organism P. aeruginosa, although they survived no better than E. coli. The GSP isolates were much more resistance to killing by UV than were the aquatic species of Halomonas reported in the literature [17]. Unlike E. coli, the GSP isolates did not appear to have an inducible, error-prone repair mecha- nism. However, they demonstrated high levels of spon- taneous mutation. Introduction The Great Salt Plains (GSP) is a hypersaline, unvegetated environment that is part of the Salt Plains National Wildlife Refuge in north-central Oklahoma. It is a barren salt flat where the briny remains of an ancient sea rise to the surface, evaporate under dry conditions, and leave crusts of white salt composed mainly of sodium and chloride. On occasion, rainfall dissolves the salt crust, creating temporary streams and ponds in which salt concentrations change rapidly. The microbiota of this site are currently under investigation as part of the Salt Plains Microbial Observatory (SPMO). Adaptation to this environment requires coping mechanisms providing tolerance to variable salinities, from near zero to saturated, high surface temperatures, continuous winds, alkaline pH, and unshaded exposure to solar UV radiation. These conditions produce a potentially desiccating environment that stresses bacteria and other microorganisms inhabiting this salt flat, and examination of the coping mechanisms of these bacteria is of interest. Desiccation and UV irradiation appear to cause similar damage to bacteria and evidence, at least in De- inococcus radiodurans, suggests that the DNA repair sys- tems that are normally associated with repair of UV- caused DNA damage are important mechanisms for desiccation-induced DNA repair as well [3]. Bacteria have several methods of repairing DNA damage. These can be conveniently classified into Light Repair and Dark Repair. It is the Dark Repair systems that are also effective in repairing desiccation-induced DNA damage [3, 18, 22]. There are at least three Dark Repair mechanisms found in bacteria. All are inducible to Correspondence to: R.V. Miller; E-mail: rum67@okstate.edu DOI: 10.1007/s00248-004-0243-z d Volume 48, 541–549 (2004) d Ó Springer Science+Business Media, Inc. 2004 541