Study type: Medical/biological study (experimental study)

Various effects on transposition activity and survival of Escherichia coli cells due to different ELF-MF signals med./bio.

By: Del Re B, Bersani F, Agostini C, Mesirca P, Giorgi G
Published in: Radiat Environ Biophys 2004; 43 (4): 265-270
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Aim of study (acc. to author)

In a previous study (see publication 9973) with weak sinusoidal magnetic fields it was shown that bacteria that had been exposed to a 50 Hz magnetic field (0.1-1 mT) gave colonies with significantly lower transposition activity as compared to sham-exposed bacteria.
These experiments have now been extended by using a pulsed-square wave magnetic field.

Endpoint

Exposure

Exposure Parameters
Exposure 1: 50 Hz
Exposure duration: continuous for 58 hours
Exposure 2: 50 Hz
Exposure duration: continuous for 58 hours
rectangular signal form

Exposure 1

Main characteristics
Frequency 50 Hz
Type
Waveform
Exposure duration continuous for 58 hours
Additional info sinusoidal signal form
Exposure setup
Exposure source
Chamber Both the active and the sham coils were maintained in an incubator at a constant temperature of 37°C. In each experiment five plates were exposed to MF and five plates were sham-exposed.
Setup The exposure system consisted of two pairs of Helmholtz coils, 23 cm diameter, 40 (20+20) turns, which were double-wrapped in order to obtain wound (active coil) or counter-wound configuration. In the counter-wound configuration, the current is the same as in the active coil but the MF is zero (sham). The test plates (Petri dishes, 9 cm in diameter) were placed in the centre of the coil system where the field uniformity was within 1%. Two MF signals were used: a) 50 Hz sinusoidal (SMF) and b) pulsed-square wave (PMF) with a duty cycle of 50% and 50 Hz repetition frequency. The root mean square (rms) of the amplitude of the square signal was the same as that of the sinusoidal signal.
Additional info The background field within the incubator was also measured: the static component (local geomagnetic field) was 35 µT and the AC component was of the order of 0.1 µT, as measured by a very sensitive probe (EMDEX II, Enertech). The experiments were conducted in a blind procedure. The data concerning the SMF have been published previously in the reference article.
Parameters
Measurand Value Type Method Mass Remarks
magnetic flux density 0.05 mT effective value measured - -
magnetic flux density 0.1 mT effective value measured - -
magnetic flux density 0.2 mT effective value measured - -
magnetic flux density 0.5 mT effective value measured - -
magnetic flux density 1 mT effective value measured - -
Measurement and calculation details

The MF was measured by means of a Bell gaussmeter (model 7010); the error in the magnetic flux density values was of the order of 2%. Due to the different wave shapes of the two signals the maximum dB/dt at 1 mT was about 0.66 T/s and 0.14 T/s for PMF and SMF, respectively. This parameter is important, being directly related to the induced electric field within the cells and/or the Petri dish. The dB/dt max linearly depends on the B field amplitude, so that the ratio between dB/dt max corresponding to 1 mT and to 0.05 mT respectively, is 1:20, for PMF as well as for SMF.

Exposure 2

Main characteristics
Frequency 50 Hz
Type
Waveform
  • rectangular
Exposure duration continuous for 58 hours
Additional info rectangular signal form
Additional info Duty cycle of 50%. The rise time of the square (from the base line to the peak) was about 1 ms.
Exposure setup
Exposure source
Parameters
Measurand Value Type Method Mass Remarks
magnetic flux density 0.05 mT effective value measured - -
magnetic flux density 0.1 mT effective value measured - -
magnetic flux density 0.2 mT effective value measured - -
magnetic flux density 0.5 mT effective value measured - -
magnetic flux density 1 mT effective value measured - -

Reference articles

Exposed system:

Methods Endpoint/measurement parameters/methodology

Investigated system:
Time of investigation:
  • after exposure

Main outcome of study (acc. to author)

Bacteria exposed to pulsed-square wave magnetic field showed a higher transposition activity compared to the controls. The increase of the transposition activity was positively correlated with the intensity of the magnetic fields. This phenomenon was not affected by any bacterial cell proliferation, since no significant difference was revealed in number and size of exposed and sham-exposed colonies.
In addition, the cell viability of E. coli was significantly higher than that of the controls when exposed to sinusoidal magnetic field, and lower than that of the controls when exposed to pulsed-square wave magnetic field.
Under these experimental conditions it was shown that exposure to pulsed-square wave magnetic field stimulates the transposition activity and reduces cell viability of bacteria, whereas exposure to sinusoidal magnetic field reduces the transposition mobility and enhances cell viability.
These findings suggest that the biological effects of magnetic fields may depend on the physical characteristics of the magnetic signal, in particular the wave shape.

Study character:

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