Magneto-aerotaxis in marine coccoid bacteria

Abstract

Magnetotactic cocci swim persistently along local magnetic field lines in a preferred direction that corresponds to downward migration along geomagnetic field lines. Recently, high cell concentrations of magnetotactic cocci have been found in the water columns of chemically stratified, marine and brackish habitats, and not always in the sediments, as would be expected for persistent, downward-migrating bacteria. Here we report that cells of a pure culture of a marine magnetotactic coccus, designated strain MC-1, formed microaerophilic bands in capillary tubes and used aerotaxis to migrate to a preferred oxygen concentration in an oxygen gradient. Cells were able to swim in either direction along the local magnetic field and used magnetotaxis in conjunction with aerotaxis, i.e., magnetically assisted aerotaxis, or magneto-aerotaxis, to more efficiently migrate to and maintain position at their preferred oxygen concentration. Cells of strain MC-1 had a novel, aerotactic sensory mechanism that appeared to function as a two-way switch, rather than the temporal sensory mechanism used by other bacteria, including Magnetospirillum megnetotacticum, in aerotaxis. The cells also exhibited a response to short-wavelength light (< or = 500 nm), which caused them to swim persistently parallel to the magnetic field during illumination.

Magneto-aerotactic bacteria deliver drug-containing nanoliposomes to tumour hypoxic regions

“…Here, we show that the magneto-aerotactic migration behaviour 2 of magnetotactic bacteria 3 , Magnetococcus marinus strain MC-1 4 , can be used to transport drug-loaded nanoliposomes into hypoxic regions of the tumour. In their natural environment, MC-1 cells, each containing a chain of magnetic iron-oxide nanocrystals 5 , tend to swim along local magnetic field lines and towards low oxygen concentrations 6 based on a two-state aerotactic sensing system 2 . We show that when MC-1 cells bearing covalently bound drug-containing nanoliposomes were injected near the tumour in SCID Beige mice and magnetically guided, up to 55% of MC-1 cells penetrated into hypoxic regions of HCT116 colorectal xenografts.…”

Magnetic irreversibility and the Verwey transition in nanocrystalline bacterial magnetite

“…17 Since then, various properties of different magnetotactic bacteria have been extensively studied. [18][19][20][21][22][23][24][25][26][27][28][29][30][31] Most of the studies were performed on the bacteria extracted from natural aquatic habitats. Recently, significant progress was achieved in vitro studying the synthesis of magnetite by various bacterial strains.…”

Sudden motility reversal indicates sensing of magnetic field gradients in Magnetospirillum magneticum AMB-1 strain

“…Sudden motility reversals in axial magnetotactic bacteria have been previously observed in response to oxygen gradients in a mechanism known as magneto-aerotaxis, because it is a 'magnetically assisted aerotaxis' (Frankel et al, 1997). In this study, we imposed sharp concentrated magnetic field gradients using thin film permalloy (Ni 80 Fe 20 ) island (B30 nm in height) to concentrate magnetic fields generated through our custom-designed Helmholtz coils that produced a uniform magnetic field (González et al, 2014).…”

“…These results have similar components to our findings with the permanent magnet as at a certain distance, the cells start swimming to the left and to the right at about equal number. Frankel et al (1997) showed that axial magnetotactic bacteria use the magnetic field lines as an axis and occasionally switch direction as they swim, and they concluded that these bacteria use a temporal sensory mechanism sampling the media and swimming up an oxygen gradient that they called two-way swimming. All of the studies mentioned above used various types of fields from rotating fields to uniform to permanent magnets.…”

“…The magnetoaerotaxis theory emerged to explain the predominance of MTB in the oxic-anoxic transition zone. The theory suggests that these organisms swim to find comfortable oxygen gradient using the Earth's magnetic field as an axis as in a 'magnetically assisted aerotaxis' (Frankel et al, 1997). The magneto-aerotaxis theory provides a more reasonable explanation, but the system could be more complex than this as these organisms may be sensing magnetic field gradients.…”