New & Noteworthy

Engineering Magnetic Yeast

March 2, 2012

Nishida and Silver have managed to make yeast magnetic.

With a bit of genetic manipulation and a hearty diet of iron, Nishida and Silver report in the latest issue of PLOS Biology that they have caused yeast cells to become magnetic. And this isn’t just a parlor trick. Their research could one day help other scientists create new therapies for the sick and new applications for research and industry.

The first step in the process was to load the yeast up with magnetic iron. The authors took a couple of different approaches.

The simplest was to grow the yeast in lots of iron. Surprisingly, without any other manipulation, this was enough to make the yeast a bit magnetic. But the authors wanted more magnetism.

To accomplish this goal, they needed to keep yeast from transporting excess iron to their vacuole where it is nonmagnetic. They did this by knocking out the gene encoding the vacuolar iron transporter, CCC1.

When grown in lots of ferric citrate, the ccc1Δ strain was about 1.8 times more magnetic than wild type. Nice, but to get even more magnetic yeast, Nishida and Silver added back the three human genes necessary to reconstitute human ferritin. This new strain was now about 2.8 times more magnetic than wild type.

None of this was really earth-shattering yet. Scientists knew that iron was needed to make a cell magnetic and that ferritin-iron complexes were a bit magnetic. What made these initial studies important was that they gave Nishida and Silver the tools to study the underlying mechanisms of magnetism.

The authors took a directed approach to study this problem and knocked out genes known to be involved in iron homeostasis or oxidative stress. Of the 60 knockout strains tested, tco89Δ was the only one to consistently be less magnetic than the wild type strain. On average it was about two fold less magnetic.

Tco89p is a nonessential part of TORC1, a complex involved in the regulation of cell growth in response to nutrients, stress, and redox states. As might be predicted from TORC1 function, the authors determined that nutrients and the redox state of the medium affected the yeast’s magnetism. They then expanded their screen to look for genes involved in carbon metabolism and mitochondrial redox that might affect magnetism and discovered several (POS5, YFH1, SNF1, and ZWF1).

The current model is that the redox state within the cell and in particular, within the mitochondria, impacts the amount of iron precipitation and hence magnetism in yeast. This is consistent with the iron deposits the authors saw in electron micrographs of the mitochondrial membrane of the magnetic yeast.

These findings should help point researchers in productive directions for engineering magnetic cells in other systems but it is only a first step. Science has a long way to go before therapies based on cell magnetism are helping patients.

More details on these magnetic yeast

by D. Barry Starr, Ph.D., Director of Outreach Activities, Stanford Genetics