Effects Of Magnetic Field On Magnetosome Formation And Expression Of MamA, Mms13, Mms6 And MagA In Magnetospirillum Magneticum AMB-1

Magnetic bacteria synthesize intracellular magnetosomes, which of nano-sized crystals of magnetic iron minerals inside membrane vesicles. Magnetosomes aligned in chains are postulated to function as biological compass needles allowing the bacterium to migrate along redox gradients, along the Earth's magnetic field lines, a behavior referred to as magnetotaxis. The superior crystalline and magnetic properties of magnetosomes have drawn attention for their potential use in bioscience, medicine and related disciplines and geobiology. Magnetosomes membrane is derived from the cytoplasmic membrane. Forty-eight proteins are identified as magnetosome specific proteins in Magnetospirillum magneticum AMB-1, and at least 13 proteins are potentially involved in formation of magnetosome. MagA,mms6,mamA and mms13 are the genes involved in iron uptake, priming and trafficking of budding vesicles,magnetite biomineralization and formation of magnetosome.Magnetosomes contain single domain magnetite crystals. Magnetic field may affect the formation of magnetosome. To investigate effects of magnetic field on magnetosome formation in Magnetospirillum magneticum AMB-1 <500nT magnetic free field space, 0.2 T constant-strength magnetic field, 50Hz-1mT pulse magnetic field and 50Hz-1mT sinusoidal magnetic field were applied to cellular cultures. Magnetic and non-magnetic pre-cultures were prepared by controlling growth conditions. They were inoculated into various growth media and incubated under different magnetic fields or geomagnetic field. Magnetism of cells was measured by using spectrophotometer coupled with applied magnetic fields and the values were described as Cmag. Magnetosome in cells were inspected and counted by transmission electron microscopy (TEM) observation. The expression of mamA, mms13, mms6 and magA was analyzed by qRT-PCR.The results showed that the magnetic free field space up-regulated the mms13 expression and down-regulated the mms6 in the cultures inoculated with magnetic cells. Only mms13 expression was up-regulated in the cultures inoculated with non-magnetic cells. Magnetic free field space seemed to postpone magnetosome formation, compared to geomagnetic field. In addition, the amount of the magnetosome chain and the average amount of magnetosome in M. magneticum AMB-1 contained magnetosome appeared decreased when magnetic free field space was applied to the cultures. The size of magnetic crystals at the middle of the magnetosome chain was big, and it was smaller gradually at the two ends of the magnetosome chain. It was likely that the existed magnetic crystals in AMB-1 could induce the formation of the new neighboring magnetosme under this condition. The magnetic crystals were homogeneous in the cultures inoculated with non-magnetic cells, suggesting that magnetite precipitation begins simultaneously from the same location within magnetosome vesicles. It also supports the hypothesis that existing magnetic crystal may influence formation of neighboring crystals.Comparing to geomagnetic field, constant-strength magnetic field impair cellular growth, but seemed to enhance magnetosome formation and up-regulated mms13 expression. The homogeneity of the magnetosome morphology was decreased but the size of the magnetosome and the average amount of magnetosome in M. magneticum AMB-1 contained magnetosome were increased. It is likely that the interaction of the magnetic field created by magnetosome in AMB-1 and the imposed magnetic field could affect the size and arrangement of the neighboring magnetosome.The pulse magnetic field up-regulated magA expression in the cultures inoculated with magnetic cells, and magA, mamA expression in the cultures inoculated with non-magnetic cells. Comparison with geomagnetic field, pulse magnetic field did not affect cellular growth, but seemed to enhance magnetosome formation. The length of the magnetosome chain appeared increased and homogeneity of the magnetosome morphology was decreased when pulse magnetic field was applied to the cultures. It is likely that magnetite precipitation induced by the neighboring magnetosome was affected by pulse magnetic field.Sinusoidal magnetic field up-regulated mms6 expression in the cultures inoculated with magnetic cells, and magA, mms6 and mamA expression in the cultures inoculated with non-magnetic cells. Sinusoidal magnetic field impaired cellular growth, but seemed to enhance magnetosome formation, compared to geomagnetic field. In addition, the homogeneity of the magnetosome morphology and linearity of magnetosome chains were impaired, but the average amount of magnetosome in M. magneticum AMB-1 contained magnetosome appeared increased when sinusoidal magnetic field applied to the cultures. It is likely that variable intensity and alternating orientation of sinusoidal magnetic field result in magnetic pole conversion in the new forming magnetosome, which affect the arrangement of the magnetosome.These results would contribute to further studies on the molecular mechanism of the effects of magnetic fields on formation of magnetosome, biotechnological application studies in magnetotactic bacteria, and the further understandings of the biological effects of magnetic fields.