E.-S.A. GAAFAR*, MAGDA S. HANAFY**, E.Y. TOHAMY***, MONA H. IBRAHIM**
* Biophysics Department, Faculty of Science, Cairo University, Egypt
** Physics department, Faculty of Science, Zagazig University, Egypt
*** Botany department, Faculty of Science, Zagazig University, Egypt
Abstract. Effect of electromagnetic field 50 Hz frequency and strength 2 mT on each of growth characteristics and pathogen city of E. coli cells have been studied. Also, the changes in the molecular structure of water soluble protein (WSP) extracted from E. coli bacteria exposed to demonstrated magnetic field were investigated through measuring each of their dielectric relaxation in the frequency range 1 kHz → 4 MHz at 4±0.05 ºC and molecular weight distribution using SDS polyacrelemid gel electrophoresis. In addition the absorption spectra of the WSP were measured at wavelength range 300–350 nm. Equal volumes of E. coli suspension were exposed to magnetic field for different periods. Most effective periods, namely, 6 and 16 h were chosen for all our experimental studies (direct and late effect – 2 h). The results indicated that there are pronounced changes in the growth characteristic curve, where suppressive effect was observed on the cell growth. Number of cells at stationary phase markedly decreased after exposure period 6 h, but there was a slight increase in the cells number at stationary phase after exposure period 16 h. Further, more remarkable changes happened in the molecular structure of extracted protein molecules after exposure periods, 6 and 16 h such as average molecular radii, shape, relaxation time and dielectric increment. Also, there were sharp decreases in the number of protein bands and in their protein amount after exposure period 6 h. However, after exposure period 16 h, number of protein bands and protein amount increased relative to the unexposed cells. Mortality rate recorded after injection with E. coli suspension exposed to 6 h was 40%, but after exposure period 16 h was 80%.
Key words: electromagnetic field, E. coli, growth rate, dielectric relaxation, molecular weight distribution, pathogen city.