When asked how, and why, she ended up making magnetic yeast, Pamela Silver, professor in the department of systems biology at the Wyss Institute for Biologically Inspired Engineering, replied: “I have always had a general interest in engineering different inputs into organisms so they can act as sensors of their different environments. They can sense light or chemicals, but sensing magnets lets them interface with machines. Also, magnetism hasn’t been studied extensively.”
In their study, Silver and Nishida 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.
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. “It was not shocking that the gene is a member of the TORC pathway, but this one was net well defined, and we were pleased that not only did its downregulation decrease magnetism, its overexpression increased it,” said Silver. 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.
As might be expected, the industry has been busting down Silver’s door. 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.
There are several biomagnetic phenomena that have not been explained at the molecular level. For example, formation of magnetic particles has been observed in degenerative disorders in humans, like Alzheimer’s disease, Parkinson’s disease, and Huntington’s disease. Magnetotactic bacteria and migratory animals can sense and move along geomagnetic field lines, and magneto-fossils too large to be bacterial hint that ancient eukaryotes may have had biogenic magnetic properties.
Nishida and Silver point out that “as magnetic interactions can be contactless, remote, and permeable, integration of magnetic properties into biological systems provide another dimension for bioengineering and therapy.” Synthetically magnetizing normally diamagnetic cells may be the first step toward applying this new dimension.
- Nishida, K., and P. A. Silver. 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+.