To study the effects of a 50 Hz sinusoidal magnetic field on the formation of magnetosomes in Magnetospirillum sp. strain AMB-1 in an effort to understand the effect of the extemal magnetic field on biomineralization and to suggest a new approach that could enhance magnetosome formation.
Magnetotactic bacteria are a diverse group of microorganisms which possess one or more chains of magnetosomes (containing magnetite). These bacteria are able to use the geomagnetic field for direction sensing, thus providing a simple model for the study of magnetite-based magnetoreception.
Cultures inoculated with either magnetic or nonmagnetic precultures were incubated under a sinusoidal magnetic field or geomagnetic field. Five parallel bacterial samples were taken at each time point (0, 2, 4, 6, 8, 10, 12, 14, 16, 20, 24, 28, 32, 36, 40, and 48 h).
| Exposure | Parameters |
|---|---|
|
Exposure 1:
50 Hz
Exposure duration:
continuous for up to 48 hr
|
|
|
Exposure 2:
Exposure duration:
continuous for up to 48 hr
|
two different cell cultures were exposed: i) cells preinoculated with enriched magnetic spirillum growth medium (containing ferric quinate) ii) cells preinoculated with iron-deficient cultures
| Frequency | 50 Hz |
|---|---|
| Type | |
| Waveform | |
| Exposure duration | continuous for up to 48 hr |
| Measurand | Value | Type | Method | Mass | Remarks |
|---|---|---|---|---|---|
| magnetic flux density | 1 mT | - | measured | - | - |
| Frequency | |
|---|---|
| Type | |
| Exposure duration | continuous for up to 48 hr |
| Exposure source |
|
|---|---|
| Setup | current flowing in opposite directions in the subcoils to eliminate the magnetic field in the coil |
| Measurand | Value | Type | Method | Mass | Remarks |
|---|---|---|---|---|---|
| magnetic flux density | 0 mT | - | measured | - | sinusoidal magnetic field |
The data showed that the sinusoidal magnetic field upregulated mms6 gene expression in the magnetically precultured cells, and magA, mms6, and mamA gene expression in the cultures inoculated with nonmagnetic cells. The sinusoidal magnetic field could block cell division, which could contribute to a decrease in the OD600 values (optical density at 600 nm was significantly decreased after magnetic field exposure compared to geomagnetic field) and an increase in the coefficient of magnetism. This could mean that the percentage of mature magnetosome-containing bacteria was increased.
The data also indicate that the sinusoidal magnetic field could lengthen magnetosome chains and increase the number of magnetic particles per cell, which could contribute to the increased cellular magnetism.
In conclusion, the results show that the sinusoidal magnetic field affected the formation of magnetosomes and the expression of some magnetosome formation related genes in Magnetospirillum magneticum/AMB-1, suggesting that magnetic bacteria had the ability to adapt the changes of the extrenal magnetic field and regulate the formation of the magnetosomes in cells. The expression of mamA and magA was shown to be more active in nonmagnetic cell cultures, suggesting that these two genes might be more activated in the de novo synthesis pathway of magnetosome.
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