Impact of gamma irradiation on the transformation efficiency for extracellular plasmid DNA.
Extracellular DNA is omnipresent in aquatic environments and is thought to be a genetic material for horizontal gene transformation between microorganisms. We studied the impact of gamma irradiation on the transformation efficiency (transformants number per ng of DNA per ml) of extracellular DNA. Plasmid pEGFP as a model extracellular DNA was irradiated by gamma rays. The transformation efficiency decreased with the increase in radiation dose. A total dose of 10Gy is normally not lethal for microorganisms but certainly affects the transformation efficiency of extracellular DNA. The decrease in the efficiency would be induced by strand breaks of extracellular DNA because the yield of both single-strand breaks (SSBs) and double-strand breaks (DSBs) increased with the increase in radiation dose. The relative transformation efficiency of SSBs and DSBs to that of covalently closed circles (CCCs) was 30.3% and 0.2%, respectively. This impact on natural transformation suggests an inability of microorganisms to acquire new characteristics which should be normally acquired.
Ishii
Nobuyoshi
N
Environmental and Toxicological Sciences Research Group, National Institute of Radiological Sciences, Anagawa 4-9-1, Chiba 263-8555, Japan. nobu@nirs.go.jp
Sakashita
Testuya
T
Takeda
Hiroshi
H
Kubota
Yoshihisa
Y
Fuma
Shoichi
S
Doi
Masahiro
M
Takahashi
Sentaro
S
D004247:DNA / Q000528:radiation effects*; D004249:DNA Damage; D004926:Escherichia coli / Q000235:genetics; D005720:Gamma Rays; D010957:Plasmids / Q000235:genetics*; D014170:Transformation, Genetic / Q000528:radiation effects
D004247:DNA