Magnetic Yeast

Figure 1. Image of modified yeast cells attracted to magnetic field.2

There are magnetic beads and yeast growth media, but now the two are combined, sort of, in the research work of Pamela Silver and Keiji Nishida from the Wyss Institute for Biologically Inspired Engineering at Harvard University.¹ These researchers have modified yeast cells to accumulate ferric iron inside the cell. The cells then are able to respond to a magnetic field (Figure 1).

The investigators in this work were able to induce magnetism in the normally diamagnetic yeast Saccharomyces cerevisiae. They grew yeast cells in the presence of ferric citrate, which allowed iron to accumulate inside the cells rather than precipitating out of the growth media. When cells were exposed to magnets, the two scientists observed the attraction. Because genes involved in iron homeostasis and redox control might contribute to the effect, Silver and Nishida knocked out 60 candidate genes to identify the ones important for achieving magnetism. Silver and Nishida were able to block expression of the protein that causes the iron sequestration, allowing the iron to circulate freely throughout the yeast cell. In this way, they created enough magnetic sensitivity in the cell to cause it to migrate toward an external magnet (Figure 2).

Figure 2. Silver and Nishida were able to create enough magnetic sensitivity in yeast cells to cause them to migrate toward an external magnet. The arrows in this image point out two of the larger concentrations of iron in a single yeast cell.

Through this analysis, they identified Tco89p, a component of target of rapamycin complex 1 (TORC1). TORC1 regulates cell growth in response to stress and nutrient and redox states. The downregulation of TORC1 resulted in a decrease in magnetism, and its overexpression increased it. TCO89 induces yeast magnetization by helping oxidize intracellular Fe²⁺ to Fe³⁺ in a dose dependent manner. They also found a number of genes involved in carbon metabolism that could affect magnetism.

Their technology could potentially be used to magnetize a variety of different cell types in medical, industrial and research applications. One company is interested in bioprocessing applications such as helping to isolate a valuable product that a cell makes but does not secrete, be it a protein, a lipid, or a biofuel. Another is interested in using the yeast as a positive control for cell sorting based on magnetism, since this paper showed that the magnetized yeast was not only attracted to magnets, but could be trapped by a magnetic column.³

In an industrial setting, magnetization could be extremely helpful as a means of targeting and isolating specific cells. Contaminated cells could be pulled out and disposed of during the processing of biological materials, and cells that are critical to a certain manufacturing process could be isolated and put to use. Magnetic cells could also be used to interact with non-living machinery. For example, magnetism could be used in tissue engineering to guide cells to layer themselves on a scaffold in a specific way. New therapies might one day be created in which cells are engineered to respond to a magnetic field by growing or healing, and implanted magnetic stem cells might one day be tracked with magnetic resonance imaging.⁴

References:

1. Nishida, K. and Silver, P.A. (2012) Induction of Biogenic Magnetization and Redox Control by a Component of the Target of Rapamycin Complex 1 Signaling Pathway. PLoS Biol 10(2): e1001269. doi:10.1371/journal.pbio.1001269.
2. Magnetic Yeast, 03/09/2012, Diana Gitig, Ph.D. http://www.biotechniques.com/news/biotechniquesNews/biotechniques-327918.html
3. ScienceDaily (Feb. 28, 2012) http://www.sciencedaily.com/releases/2012/02/120228190922.htm
4. New “Magnetic Yeast” Could be Significant Step in Harnessing Nature’s Magnetic Capabilities http://wyss.harvard.edu/viewpressrelease/78

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