Effect of gamma-ray irradiation on Escherichia coli motility

Abstract

The effects of ionizing radiation on bacteria are generally evaluated from the dose-dependent survival ratio, which is determined by colony-forming ability and mutation rate. The mutagenic damage to cellular DNA induced by radiation has been extensively investigated; however, the effects of irradiation on the cellular machinery in situ remain unclear. In the present work, we irradiated Escherichia coli cells in liquid media with gamma rays from 60Co (in doses up to 8 kGy). The swimming speeds of the cells were measured using a microscope. We found that the swimming speed was unaltered in cells irradiated with a lethal dose of gamma rays. However, the fraction of motile cells decreased in a dose-dependent manner. Similar results were observed when protein synthesis was inhibited by treatment with kanamycin. Evaluation of bacterial swimming speed and the motile fraction after irradiation revealed that some E. coli cells without the potential of cell growth and division remained motile for several hours after irradiation.

Expression of the lacZ gene in Escherichia coli irradiated with gamma rays

“…The results suggested that the cells retain some active machinery required for gene expression (induction of transcription by IPTG and subsequent translation) for at least 2 h after irradiation with gamma rays, despite having lost the ability to grow and divide. This is consistent with the previous observation that some gamma-irradiated E. coli cells had continued to be motile several hours after irradiation (Atsumi et al 2014). Low activity of gene expression at time ¼ 0 (just after irradiation) may be caused by low temperature condition (room temperature) during the irradiation.…”

“…Recently, we have reported that the flagellar motor of Escherichia coli strain AW405 remains active at a certain level after bombardment with a proton beam (Kato, Meissl, Umezawa, Ikeda, & Yamazaki, 2012) and irradiation with gamma rays (Atsumi, Fujimoto, Furuta, & Kato, 2014), even though the cells do not retain their ability to grow after such an insult. Because bacterial motility requires several physiological processes, such as energy metabolism, respiratory chains to maintain electrochemical potential across the membrane, and many others (Berg, 2003), these data indicate that bacterial cells exhibiting arrest of cell growth after irradiation still retain a certain level of physiological activity.…”

Motility of Escherichia Coli After Irradiation With Gamma-Rays

“…Bacterial cells were cultured in modified T-broth consisting of 0.5% (w/v) polypeptone (Nippon Seiyaku, Tokyo, Japan) and 0.5% (w/v) NaCl. Bacterial cells in the logarithmic growth stage were harvested as described previously [7], with minor modifications, and were suspended in motility medium (10 mM potassium phosphate, 0.1 mM EDTA, and 10 mM sodium lactate) after washing with the same medium. Briefly, cells were cultured in 140 ml of modified T-broth for 3.5 h at 37 °C with shaking, and were harvested by centrifugation (3000 × g, 6 min).…”

“…The cell suspension was divided into five samples that were subjected to gamma irradiation (0.5 kGy, 1.0 kGy, 2.0 kGy, 4.0 kGy, and no irradiation as a control). The samples were exposed to gamma rays from 60 Co in a water pool in Radiation Research Center, Osaka Prefecture University, at room temperature for the period required to administer the designated dose as described previously [7].…”

“…Recently, we reported the flagellar motor activity of E. coli strain AW405 after the bombardment with an accelerated proton beam [6] and gamma rays [7], and demonstrated its robustness in the presence of a radiation dose that was shown to inhibit the bacterial cell division.…”