Kazumasa Okuno

Effect of homogeneous and inhomogeneous high magnetic fields on the growth of Escherichia coli

Abstract The growth of Escherichia coli B was investigated under homogenous 7 Tesla (T) magnetic field, and inhomogeneous 5.2∼6.1 T and 3.2∼6.7 T magnetic fields which are produced by a newly constructed superconducting magnet biosystem (SBS). These high magnetic field adversely affected on the growth of the bacterium in the early logarithmic growth phase. However, in the stationary phase, the cell number under a high magnetic field was about 2∼3 times higher than that of a control, indicating that the magnitude of the decrease in the cell number was reduced by the high magnetic field. The effect of the inhomogeneous magnetic field was much stronger than that of the homogeneous one. The high magnetic field was found to affect the cells of the bacterium differently, depending on the growth phases.

Effect of super high magnetic field on the growth of Escherichia coli under various medium compositions and temperatures

Abstract When two strains of Escherichia coli were grown under a super high magnetic field (11.7 Tesla) in complex medium, the growth was stimulated in comparison with that in the geomagnetic field. When the bacteria were grown in synthetic medium, the growth rates were reduced significantly. As a result of the addition of casamino acids to the synthetic medium, the growth was shifted from a reduced state to a stimulated one, suggesting that certain amino acids are responsible for the phenomenon. Twenty amino acids were thus added individually to minimal medium; some of these amino acids shifted the reduced growth state to accelerated or normal growth. The critical concentration of glutamic acid for the growth shift was determined to be 0.01–0.1 mg/l. When the bacteria were grown at temperatures lower than the optimal temperature for growth, the 11.7 T magnetic field enhanced the growth rate irrespective of media used, while at higher temperatures reduced growth became significant in accordance with the increase in temperature. A potential use of the high magnetic field as a control factor in biological system is suggested.

High magnetic field enhances stationary phase-specific transcription activity of Escherichia coli.

When Escherichia coli B was aerobically grown at 37 degrees C under inhomogeneous 5.2-6.1 Tesla (T) magnetic fields in the superconducting magnet biosystem (SBS), the cell number in the stationary phase after the growth had leveled off, was about 3 times higher than that under a geomagnetic field. When the E. coli defective in the rpoS gene which encodes a sigma factor, sigmaS of RNA polymerase and is specifically expressed in the stationary phase was cultivated at 37 degrees C in SBS, such enhancement of cell survival was significantly reduced. The E. coli cells carrying rpoS-lacZ fusion gene or other rpoS dependent genes fused with lacZ were grown, significant increase in the activity of beta-galactosidase was observed in the stationary phase under high magnetic field. These data suggest that enhancement of the transcription activity in stationary phase is involved in the higher survival of the cells under magnetic field.

Effect of high magnetic field on the growth of Bacillus subtilis measured in a newly developed superconducting magnet biosystem

Abstract A new superconducting magnet biosystem (SBS) has been developed, which can provide a magnetic field of 0.5–7 T, where biological reactions can be conducted under temperature-controlled conditions. The aerobic growth of a bacterium, Bacillus subtilis MI113, was investigated under homogeneous (7 T) and inhomogeneous (5.2–6.1 T) magnetic fields in a shaken culture. In the stationary phase, the cell number in an inhomogeneous magnetic field was about twofold higher than that of the reference, indicating that the magnitude of the decrease in the cell number was reduced by the high magnetic field. The slower decline in the cell number in a magnetic field was due to the slower death rate of the vegetative cells. The inhibition of spore formation from vegetative cells was also observed in a magnetic field, which was reflected by the reduced activity of alkaline phosphatase. Genetically transformed B. subtilis MI113 (pC112) produced a higher concentration of a lipopeptide antibiotic, surfactin, in the stationary phase in an inhomogeneous magnetic field due to the higher cell number of the transformant in the magnetic field.

Drastic high magnetic field effect on suppression of Escherichia coli death

When Escherichia coli B was aerobically grown in a medium containing one-fourth the concentration of the LB medium supplemented with glutamic acid at 43 degrees C under an inhomogeneous 5.2-6.1 T magnetic field, the number of cells in the stationary phase under the high magnetic field was 100,000 times higher than that under a geomagnetic field. The finding that the amount of sigma S factor encoded by the rpoS gene under the high magnetic field was larger than that under the control geomagnetic field indicated that the activity of the rpoS gene was affected by the high magnetic field.

Twelve hours exposure to inhomogeneous high magnetic field after logarithmic growth phase is sufficient for drastic suppression of Escherichia coli death

When Escherichia coli B was aerobically grown at 43 degrees C in a medium whose concentration was one-fourth that of the Luria-Bertani (LB) medium supplemented with 1.5 g/l of glutamic acid, drastic cell death was observed after the end of the logarithmic growth phase. However, when the same experiment was conducted under inhomogeneous 5.2-6.1 T magnetic field, cell death was extremely suppressed and the ratio of viable cell number under high magnetic field to that under geomagnetic field reached as much as 100,000. When the magnetic field exposure was restricted to 12 h after the logarithmic growth phase, a similar high degree of suppressive effect on the death was observed. The findings that the amount of sigma S protein encoded by the rpoS gene under the high magnetic field was larger than that under the geomagnetic field, and that the magnetic field effect disappeared when the rpoS gene-deficient strain was cultivated under the high magnetic field, suggest the interaction of magnetic field with a stationary phase specific gene.

Effect of a 7-tesla homogeneous magnetic field on mammalian cells.

When two types of mammalian cells, mouse leukemia cells, P388, and Chinese hamster fibroblast cells, V79, were grown under a 7-tesla (T) homogeneous magnetic field which was produced by a newly constructed superconducting magnet biosystem (SBS), the growth pattern of cells under 7 T magnetic field and the geomagnetic field control showed no differences. The DNA distribution of the two cells was compared by flow cytometry after exposure to 7 T for 3 and 24 h, but there was no significant differences between magnet-exposed cells and unexposed cells. When the two types of cells were exposed to different concentrations of the antitumor agent, bleomycin (BLM), for 3 h under 7 T, their viable cell numbers were almost the same as that of the control although sensitivity to BLM was different between the two cells. These results suggest that the 7 T homogeneous magnetic field exerts no adverse effects on mammalian cells.

New 7 T superconducting magnet system for bacterial cultivation

Abstract A new superconducting magnet system for bacterial cultivation has been developed. The superconducting magnet has a horizontal room temperature bore with a diameter of 160 mm, and provides a homogeneous magnetic field of 7 T ± 0.5% for a 200 mm long × 100 mm diameter region. This homogeneous field region contains an incubator, where bacteria are cultivated aerobically at 10–70 °C ± 0.1 °C while being shaken. The culture exposed to the high magnetic field is compared with a control culture incubated at below geomagnetic field strength. Cultivation of Escherichia coli was carried out both in homogeneous and in inhomogeneous fields, and 1.4–3.6 times the number of viable cells of the control culture was observed in a stationary phase.

Effect of super high magnetic field on the growth ofEscherichia coli

SummaryAuxotrophic mutants ofEscherichia coli were grown under the super high magnetic field (11.7 Tesla) and the effect of the field both on the growth and mutation frequency of the bacteria was investigated. When the bacteria were cultivated in complex media, the growth was stimulated under 11.7T in comparison with that in geomagnetic field. When the bacteria were grown in synthetic media, the growth rates were reduced significantly. Neither mutagenic nor lethal effects of the magnetic field on the bacteria was observed. A potential application of high magnetic strength as a controlling factor of the bacterial growth was implied.

Change in broth culture is associated with significant suppression of Escherichia coli death under high magnetic field

When Escherichia coli B was cultivated under an inhomogeneous magnetic field of 5.2-6.1 T, a significant 100,000-fold suppression of cell death was observed [Bioelectrochemistry 53 (2001) 149]. The limited magnetic field exposure for 12 h after logarithmic growth phase was sufficient to observe similar suppressive effects on cell death [Bioelectrochemistry 54 (2001) 101]. These results suggest some possible changes in either the medium or the cells during the magnetic field exposure. When the cell-free filtrate of the broth cultured under the magnetic field for 10 h and the cells of E. coli cultivated under the geomagnetic field for 30 h were mixed, and the mixture was subsequently cultivated under the geomagnetic field, the number of cells observed in the filtrate exposed to the high magnetic field was 20,000 times higher than that in the filtrate exposed to the geomagnetic field. When the cells cultivated under the magnetic field for 10 h and the cell-free filtrate of the broth culture exposed to the geomagnetic field were mixed, only a 50-fold difference in the number of cell between under the magnetic field and under the geomagnetic field was observed. This suggests that the filtrate of the broth culture exposed to the magnetic field is primarily responsible for the cell death suppression. It was also revealed that the small difference in pH of the filtrates of the broth culture between under the magnetic field and under the geomagnetic field was critical for the cell death suppression.