Tikalon Blog by Dev Gualtieri

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Magnetic Yeast

March 7, 2012

When people think about animal magnetism , it's more likely in the context of one of the many male and female pop stars . Even Britney Spears , at her advanced age (for pop stars) of thirty, can still give a seductive performance, as evidenced in her recent music videos .[1]

Although animal magnetism is properly described as just the sociological quality known as charisma , it was once believed that a form of magnetism was really involved. Franz Mesmer , from who we get the term, mesmerize , thought that a type of magnetism, which was not the physicist's concept of magnetism , permeated the bodies of all animals , and one animal could influence another through such magnetism.

Such an idea sounds strange to today's scientists , but it explained a lot of things in the eighteenth century in which it was introduced. Even today, magnetic cures abound for many ailments , as I mentioned in a previous article (Electricity, Magnetism and Morality, September 28, 2011). There was a period when electricity was promoted as a medical cure, also.

There is, however, a modern science of magnetism of animals that's quite distinct from these. Some animals are known to possess receptors for magnetic field , a property known as magnetoception . Such a magnetic sense would have an obvious evolutionary advantage to animals that migrate over long distances. Homing pigeons , which do not migrate, but are known to be good direction finders , have been found to have this magnetic sense.

The magnetically active material in magnetoception is magnetite ,[2] which is located in the ethmoid bones .[3] These bones are located just behind the nose , between the eyes . Magnetite has been found in these bones for humans , also, but its occurrence must be vestigial .[3] It's hard to posit any evolutionary advantage for this in a species that generally remains within a few hundred miles of its birthplace for its entire life.

Figure caption

Monarch butterfly
(Danaus plexippus)

Monarchs have been found to use magnetoception for navigation.[4]

(Via Wikimedia Commons .)

It's not just the higher organisms that respond to magnetic fields. Magnetotactic bacteria are also known to exist.[5-6] These were discovered by Richard P. Blakemore in 1975, and they were found to respond to magnetic fields as small as 0.5 gauss.[5] The Earth's magnetic field ranges from about 0.25 - 0.65 gauss, depending on location.

In magnetoception, the organism participates in its response to a magnetic field. In magnetotaxis , however, the response is physical, not physiological. Magnetic fields exert an actual force on the bacteria. In a recent feat of bioengineering , scientists from Harvard University have succeeded in inducing magnetotaxis in bacteria that are not naturally magnetotactic.[7-10]

To make an organism magnetotactic, you need to introduce magnetic material into its structure. The naturally occurring magnetotactic bacteria have genes that are responsible for production of such material. To make budding yeast bacteria (Saccharomyces cerevisiae ) magnetotactic, the Harvard research team deleted a gene that moves excess iron into vacuoles , which are storage containers in the cell. Deletion of this gene allowed iron to accumulate in the cells when they were immersed in an growth medium enriched in iron with ferric citrate .

Figure caption

The arrows in this photomicrograph identify two large concentrations of iron in a yeast cell.

There's enough magnetic material present to cause such cells to move in a magnetic field.

(Harvard University image by Pamela Silver and Keiji Nishida , used with permission).

Preventing the cells from sequestering iron did make the bacteria sensitive to magnetic field, but the Harvard team found a way to enhance the magnetotaxis. They modified the bacteria to produce human ferritin proteins, which further prevents storage of iron in the cell. Addition of another protein that regulates cell metabolism also enhanced the magnetotaxis.[8]

Magnetotaxis in bacteria can be useful in industrial processes as a way to separate cells. Also, magnetism could be used to guide cells to form layers for tissue engineering . This work was funded by the Japan Society for Promotion of Science Postdoctoral Fellowship for Research Abroad , the ONR Multidisciplinary Research Initiative , and the Wyss Institute of Biologically Inspired Engineering .[8]

Figure caption

TEM image of Magnetospirillum gryphiswaldense(MSR-1), a freshwater Gram-negative microaerophilic bacterium.

The bacteria synthesize magnetite (Fe₃O₄) nanoparticles that are arranged in a chain inside the cell allowing the organism to orient itself in Earth's geomagnetic field.

(Photograph by Zachery Oestreicher and Brian H. Lower . Used with permission.)

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