@misc{oai:repo.qst.go.jp:00069134,
 author = {Ishii, Nobuyoshi and Sakashita, Tetsuya and Takeda, Hiroshi and Kubota, Yoshihisa and Fuma, Shoichi and Doi, Masahiro and Takahashi, Sentaro and 石井 伸昌 and 坂下 哲哉 and 武田 洋 and 久保田 善久 and 府馬 正一 and 土居 雅広 and 高橋 千太郎},
 month = {Oct},
 note = {DNA is an abiotic substance, and it is an essential substance as a genetic material for all organisms.  However, DNA is not always present within cell.  In aquatic environments, a form of naked extracelluar DNA is omnipresent at concentrations from 0.5 to 88 ug per liter.  Extracellular DNA can serve as a source of carbon and energy supporting microbial growth and is required for bacterial biofilm formation.  In addition, extracellular DNA has a sufficient molecular weight to retain its genetic function.  In fact, gene sequences had been detected in the extracellular DNA fraction. Recently, we demonstrated that extracellular plasmid DNA was released from actively growing bacteria and the released extracellular DNA was able to be used for bacterial transformation.  Therefore, extracellular DNA is an important component of aquatic ecosystems.
    Issues for geological disposal of radioactive waste, high-background radiation areas, and severe nuclear accidents have raised considerable concern and drawn attention to the effect of ionizing radiation on the environment.  Previous studies have extensively examined the relative radiosensitivities of different species and classes of organisms.  Since ecosystems in the environment consist of both biotic and abiotic components, not only the effects of gamma radiation on organisms in the environment but also the effects on physical structures and chemical forms of abiotic materials are required.  However, there are few data on the effect of gamma irradiation on the abiotic components.  In the present study, we focused on extracellular DNA as an abiotic component.
    A number of studies have been carried out on the effects of gamma irradiation on extracellular DNA and they have revealed the molecular and cellular mechanisms related to the biological damage by ionizing radiation.  However, little is known so far about as damages of the retained function of extracellular DNA, which is available for natural genetic transformation in aquatic environments.  We, therefore, studied the effect of gamma irradiation on the extracellular DNA transformation efficiency (the number of transformed cells [transformants] generated by a unit weight of extracellular DNA).
\n    We are grateful to Prof. K. Hieda for advice on the agarose gel electrophoresis.  This work was supported in part by the Ministry of Education, Culture, Sports, Science and Technology, Grant-in-Aid for Young Scientist (B), 18710051., the 13th International Symposium on River and Lake Environment},
 title = {Effect of gamma irradiation on the transformation efficiency for extracellular plasmid DNA},
 year = {2007}
}