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Applied and Environmental Microbiology, April 2000, p. 1489-1492, Vol. 66, No. 4
0099-2240/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

Ionizing-Radiation Resistance in the Desiccation-Tolerant Cyanobacterium Chroococcidiopsis

Daniela Billi,1,* E. Imre Friedmann,1 Kurt G. Hofer,1 Maria Grilli Caiola,2 and Roseli Ocampo-Friedmann3

Department of Biological Science, Florida State University, Tallahassee, Florida 32306-11001; Department of Biology, University of Rome "Tor Vergata," I-00133 Rome, Italy2; and Department of Biological Sciences, Florida Agricultural and Mechanical University, Tallahassee, Florida 323073

Received 12 October 1999/Accepted 7 January 2000

The effect of X-ray irradiation on cell survival, induction, and repair of DNA damage was studied by using 10 Chroococcidiopsis strains isolated from desert and hypersaline environments. After exposure to 2.5 kGy, the percentages of survival for the strains ranged from 80 to 35%. In the four most resistant strains, the levels of survival were reduced by 1 or 2 orders of magnitude after irradiation with 5 kGy; viable cells were recovered after exposure to 15 kGy but not after exposure to 20 kGy. The severe DNA damage evident after exposure to 2.5 kGy was repaired within 3 h, and the severe DNA damage evident after exposure to 5 kGy was repaired within 24 h. The increase in trichloroacetic acid-precipitable radioactivity in the culture supernatant after irradiation with 2.5 kGy might have been due to cell lysis and/or an excision process involved in DNA repair. The radiation resistance of Chroococcidiopsis strains may reflect the ability of these cyanobacteria to survive prolonged desiccation through efficient repair of the DNA damage that accumulates during dehydration.

* Corresponding author. Present address: Department of Biochemistry, Virginia Polytechnic Institute and State University, 205 Engel Hall, W. Campus Drive, Blacksburg, VA 24061. Phone: (540) 231-8435. Fax: (540) 231-9070. E-mail: dbilli{at}vt.edu.

Applied and Environmental Microbiology, April 2000, p. 1489-1492, Vol. 66, No. 4
0099-2240/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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