Righi Henriette, Arruda-Neto João D T, Gomez José G C, da Silva Luiziana F, Somessari Elizabeth S R, Lemos Aline C C
Physics Institute, University of Sao Paulo, Sao Paulo, Brazil.
Institute for Biomedical Sciences, University of Sao Paulo, Sao Paulo, Brazil.
J Biol Phys. 2020 Sep;46(3):309-324. doi: 10.1007/s10867-020-09554-5. Epub 2020 Aug 18.
The extremophilic bacterium Deinococcus radiodurans displays an extraordinary ability to withstand lethal radiation effects, due to its complex mechanisms for both proteome radiation protection and DNA repair. Published results obtained recently at this laboratory show that D. radiodurans submitted to ionizing radiation results in its DNA being shattered into small fragments which, when exposed to a "static electric field' (SEF), greatly decreases cell viability. These findings motivated the performing of D. radiodurans exposed to gamma radiation, yet exposed to a different exogenous physical agent, "static magnetic fields" (SMF). Cells of D. radiodurans [strain D.r. GY 9613 (R1)] in the exponential phase were submitted to Co gamma radiation from a gamma cell. Samples were exposed to doses in the interval 0.5-12.5 kGy, while the control samples were kept next to the irradiation setup. Exposures to SMF were carried out with intensities of 0.08 T and 0.8 T delivered by two settings: (a) a device built up at this laboratory with niobium magnets, delivering 0.08 T, and (b) an electromagnet (Walker Scientific) generating static magnetic fields with intensities from 0.1 to 0.8 T. All samples were placed in a bacteriological incubator at 30 °C for 48 h, and after incubation, a counting of colony forming units was performed. Two sets of cell surviving data were measured, each in triplicate, obtained in independent experiments. A remarkable similarity between the two data sets is revealed, underscoring reproducibility within the 5% range. Appraisal of raw data shows that exposure of irradiated cells to SMF substantially increases their viability. Data interpretation strongly suggests that the increase of D. radiodurans cell viability is a sole magnetic physical effect, driven by a stochastic process, improving the efficiency of the rejoining of DNA fragments, thus increasing cell viability. A type of cut-off dose is identified at 10 kGy, above which the irradiated cellular system loses recovery and the cell survival mechanism collapses.
极端嗜热菌耐辐射奇异球菌具有非凡的能力来抵御致命的辐射效应，这归因于其蛋白质组辐射防护和DNA修复的复杂机制。本实验室最近发表的结果表明，耐辐射奇异球菌受到电离辐射后，其DNA会破碎成小片段，而当这些小片段暴露于“静电场”（SEF）时，细胞活力会大幅下降。这些发现促使研究人员对耐辐射奇异球菌进行了另一项实验，使其暴露于γ辐射下，但同时暴露于另一种外源物理因子“静磁场”（SMF）中。处于指数生长期的耐辐射奇异球菌[菌株D.r. GY 9613（R1）]细胞接受来自伽马细胞的钴γ辐射。样本接受的剂量范围为0.5 - 12.5千戈瑞，而对照样本则放置在辐照装置旁边。静磁场暴露通过两种设置进行，强度分别为0.08特斯拉和0.8特斯拉：（a）本实验室用铌磁铁构建的装置，可产生0.08特斯拉的磁场；（b）一个电磁铁（沃克科学公司生产），可产生强度为0.1至0.8特斯拉的静磁场。所有样本都放置在30℃的细菌培养箱中培养48小时，培养后进行菌落形成单位计数。测量了两组细胞存活数据，每组数据重复测量三次，且实验相互独立。结果显示两组数据集之间具有显著的相似性，强调了在5%范围内的可重复性。对原始数据的评估表明，受辐照细胞暴露于静磁场中会显著提高其活力。数据解读有力地表明，耐辐射奇异球菌细胞活力的增加是一种单纯的磁物理效应，由一个随机过程驱动，提高了DNA片段重新连接的效率，从而增加了细胞活力。在10千戈瑞处确定了一种截止剂量，高于此剂量，受辐照的细胞系统失去恢复能力，细胞存活机制崩溃。
