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PRADO, G. R. Study of resistance of D. radiodurans to the combined action of ionizing radiation with an electric or magnetic fields exogenous. 2011. 200 p. Ph. D. Thesis (Biotechnology) Instituto de Ciencias Biomedicas, Universidade de Sao Paulo, Sao Paulo, 2011. The key goal in radiotherapy is to maximize damages in a tumor while minimizing them in nearby health tissues. Several strategies have been worked out toward the enhancement of cellular radiosensibility, as the use of exogenous fields. It is studied in this work the resistance of Deinococcus radiodurans to the combined action of conventional and non conventional radiations, with external agents (electric and magnetic fields). D. radiodurans is a bacterium having an extraordinary ability to cope with lethal and mutagenic agents harmful to the DNA, particularly ionizing radiations as gammas and UV. Given its high radioresistance and fast growing, D. radiodurans has been used as solid tumors simulators. Peculiarities associated with radioresistance at the exponential and stationary phases were delineated from growing curves. By measuring survival curves information on radiosensibility was obtained. In gamma irradiation D. radiodurans exhibited repairing shoulders of 2 and 8 kGy at the exponential and stationary phases, respectively. When gamma irradiations were combined with expositions to the electric field the repairing shoulders were reduced to 1 and 4 kGy at the exponential and stationary phases, respectively. Radioresistance was similar in both growing phases when the number of cells were approximately equalized in these two processes. On the other hand, when gamma irradiations were combined with expositions to the magnetic field the repairing shoulders were reduced to 4 and 6 kGy at the exponential and stationary phases, respectively. In irradiations with electron beams the repairing shoulder at the exponential phase was totally depleted, while at the stationary phase it was only 1 kGy. The findings of this work revealed new and important information on the radioresistance of D. radiodurans, while providing hints to the improvement of radiotherapy protocols in association with exogenous physical agents. Key-words: D. radiodurans. Gamma radiation. Electron beams. Electric and magnetic fields. Radiosensibility.

Estudo da resistência de D. radiodurans à ação combinada de radiações ionizantes com campos elétricos ou magnéticos exógenos.