Strong static magnetic field and the induction of mutations through elevated production of reactive oxygen species in Escherichia coli soxR.
OBJECTIVE
Although strong static magnetic fields (SMF) are supposed to have the potential to affect biological systems, the effects have not been evaluated sufficiently. Experiments should be performed with a powerful SMF-generating apparatus to evaluate the biological effects of SMF.


METHODS
An Escherichia coli mutation assay was used to assess the mutagenic effects of strong SMF. Various mutant strains of E. coli were exposed to up to 9 Tesla (T) for 24 h and the frequencies of rifampicin-resistant mutations were then determined. The expression of the soxS::lacZ fusion gene was assessed by measurement of beta-galactosidase activity.


RESULTS
The results for survival or mutation were obtained with wild-type E. coli strain GC4468 and its derivatives defective in DNA repair enzymes or redox-regulating enzymes were all negative. On the other hand, the mutation frequency was significantly increased by the SMF exposure in soxR and sodAsodB mutants, which are defective in defence mechanisms against oxidative stress. Furthermore, the expression of superoxide-inducible soxS::lacZ fusion gene was stimulated 1.4- and 1.8-fold in E. coli when exposed to 5 and 9 T, respectively.


CONCLUSIONS
These results indicate that strong SMF induce mutations through elevated production of intracellular superoxide radicals in E. coli.
Zhang
Q-M
QM
Laboratory of Radiation Biology, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan.
Tokiwa
M
M
Doi
T
T
Nakahara
T
T
Chang
P-W
PW
Nakamura
N
N
Hori
M
M
Miyakoshi
J
J
Yonei
S
S
D001426:Bacterial Proteins / Q000235:genetics*; D004926:Escherichia coli / Q000235:genetics* / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000235:genetics*; D015870:Gene Expression; D005798:Genes, Bacterial; D007763:Lac Operon; D008280:Magnetics / Q000009:adverse effects*; D009154:Mutation; D017382:Reactive Oxygen Species / Q000378:metabolism*; D015534:Trans-Activators / Q000235:genetics; D014157:Transcription Factors / Q000235:genetics*
D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D017382:Reactive Oxygen Species; D015534:Trans-Activators; D014157:Transcription Factors; C070724:SoxR protein, Bacteria; C070725:SoxS protein, E coli