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Show ACUTE EMR EXPOSURE YIELDS NO DNA BREAKS IN MODEL SALMONELLA TYPHIMURIUM SYSTEM, BUT PROVIDES EVIDENCE OF 2° CROSS STRESS* PROTECTION Parley A. Williams, (Richard J. Ingebretsen, A/ID, PhD) Department of Physics, University of Utah he aim of this study was to asses the effects of a 60 Hz sinusoidal electromagnetic field on in vivo genetic homologous recombination including associated biological pathways. The topic of this study is significant because, while others have found similar results in vitro, this is the first of its kind to identify a significant effect in vivo. The investigative strategy included acute (4 h) exposure of liquid Salmonella cultures to a 60 Hz magnetic field (14.6 mT @ peak strength) in an event counter assay and a viability assay. In the instance of the viability assay, the EMR exposure was followed by a secondary heat stress exposure (l0min at 52 C). The 4 hour exposure was administered by a cyclic sequence of 5 minute exposure followed by a 10 minute resting period. After EMR and secondary stress (viability assay) exposure, the Salmonella were plated on rich media plates and incubated for 12 to 18 hours at 37 C. The event counter assay (RD978) involves a chromosomal duplication that, following recombination, causes a visual change in the color of Salmonella typhimurium colo-nies. The number of blue (non-recombinant) and white (recombinant) colonies for EMR pretreated cultures were counted and compared to the control to detect any statistically significant increase in recombination events (signifying an increase in DNA strand breaks). From a statistical two-tailed hypothesis t-test with unequal variances it can be assumed that both the control and EMR exposed cells exhibited the same rate of recombination, indicating no significant increase in DNA stand breaks due to EMR exposure. In the viability assay (RD2010, RD821), the number of surviving colonies (RecA-Dis-abled) from EMR pretreated cultures was compared to the number of surviving colonies from the control to asses any change in viability resulting from EMR-induced DNA damage. The results show that the Salmonella typhimurium pretreated with EMR exhibited an increased viability of 7-9 times that of the control. The strains of Salmonella used for this study had been engineered to lack RecA protein synthesis. This result provides evidence that acute EMR exposure provides secondary cross stress protection in the instance of heat. Further investigation is required to discover the cause for this protection from heat stress. A study of the effects of HSP syn-thesis and SOS responses in combination with EMR exposure is recommended for further investigation. Parley A. Williams Business *Disabled RecA pathway. Strain RD 2010, RD 821 |
