Thesis (Ph.D.) - Cairo University - Faculty of Science - Department of Biophysics

Agrobacterium tumefaciens causes crown gall disease of wide range of dicotyledonous (broad-leaved) plants species by introducing its T-DNA into the genome resulting in economic loss of plant yield. Many trials have been carried out all over the world to control theses bacterial infections using commercial chemicals without much success. Therefore the aim of the present work was to demonstrate a new method for the control of microbial cell growth, through the interference with the bioelectric signals generated from the microbe during cell division by extremely low frequency electromagnetic fields (EMF), pulsed electric field (PEF) or pulsed magnetic field (PMF) at resonance frequency. Isolated A. tumefaciens inoculated in standard laboratory LB broth medium was exposed to different extremely low frequencies of square amplitude modulated waves (QAMW), (PEF) and (PMF) in the range 0.1 Hz to 1.3 Hz to determine the resonance frequency of growth inhibition. For square amplitude modulated waves (QAMW), the carrier was 10 MHz sine wave with amplitude ± 10 Vpp which was modulated by a second wave generator with a modulation depth of ± 2Vpp and constant field strength of 200V/m. The magnetic field and electric field strengths were 50mG and 200V/m respectively. The bacterial cells were then exposed to varied exposure time in the range 15-150 min at the inhibiting resonance frequency of bacterial growth at 28{u00B0}C. The results showed that there was highly significant inhibition effect for A. tumefaciens exposed to 1.0 Hz QAMW, PEF or PMF for 90 min, while there was no change in the bacterial growth for samples exposed to other frequencies in the range 0.1-1.3 Hz at different exposure time.The data confirmed that there was a resonance frequency only at 1.0 Hz resulted in an inhibition effect on the growth rate and the number of cells of A. tumefaciens

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