Yeast Gets a Magnetic Personality

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Scientists at Harvard's Wyss Institute have genetically engineered an organism to sense magnetic fields, showing that it's possible to make organisms react to magnetism even when they normally don't. 

The work points to a lot of applications in medicine, industry and research. For example, cells sensitive to magnetic fields tend to align themselves in a single direction like tiny compass needles. That means one could move them in a specific direction to, say, build up tissue into a specific shape. The technique could be used to target therapeutic cells at diseases and would also be useful in magnetic resonance imaging.

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Some species of bacteria sense magnetism because they have tiny bits of iron or iron compounds inside them. But most plants and animals don't, and when their cells are exposed to iron, they try to stuff it away into tiny, hollow spaces called vacuoles. (Many animals, including humans, need iron to survive, but that iron is metabolized in very different ways).

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Researchers Pamela Silver and Keiji Nishida took ordinary yeast and grew it in a medium containing iron. The yeast cells took in the iron and stored it inside vacuoles. The scientists then put a magnet under the plate where the yeast was and saw the yeast was slightly magnetic.

Nishida added a protein called ferritin, which joins with iron and prevents it from becoming toxic. He also used genetic engineering to block the yeast's ability to produce a protein that's used to carry the iron into the cell’s vacuoles. That let the iron circulate freely throughout the yeast cell and made the cell sensitive enough that it would migrate toward an external magnet.

One interesting effect was that the genetically altered yeast stored iron in its mitochondria. The altered yeast was also about three times as magnetic as wild yeast, which was just given iron supplements.

The researchers found that other proteins in the yeast — also found in other animals, including humans — could be combined to amp up the magnetism. The existence of these proteins in other animals means that with a little genetic tweaking, other one-celled creatures that could become tiny, living bar magnets.

Photo: Yeast made sensitive to magnetism by altering how it reacts to iron. The arrows point to two of the larger concentrations of iron in a single yeast cell.

Credit: Harvard Medical School