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Sopping up Uranium with Yeast

March 23, 2012

Yeast might help detoxify nuclear waste like this. Image courtesy of Wikimedia Commons.

Yeast may be good for more than making bread and beer or understanding how eukaryotes like humans work.  They may also be useful for cleaning up high volume, low concentration waste uranium (think uranium waste water).

The idea would be to add yeast to the contaminated area, have the yeast take the uranium up, put the yeast into radioactive waste and repeat with new yeast.  This would be a relatively cheap, simple way to detoxify this form of radioactive waste.

An obvious way to improve on this idea is to identify yeast strains that can accumulate more uranium than the wild type strain.  In a new study out in Geomicrobiology Journal, Sakamoto and coworkers have started down this path by identifying genes that allow yeast to grow in the presence of uranium and those involved in uranium accumulation.

They did this with two different screens using a set of 4,098 non-essential gene deletion strains.  In the first they identified 13 strains that grew more poorly than wild type at 0.5 mM uranium.  And in the second, they identified 17 strains that accumulated less uranium than wild type.

There was very little overlap between the two sets of strains suggesting different pathways (or sets of pathways) may be involved in accumulation and growth.  However, there were two deletion strains that showed up in both screens.  Both of the identified genes, PHO86 and PHO2, are involved in phosphate metabolism.

These genes definitely make sense.  A number of previous studies had hinted strongly that uranium accumulates on the surface of yeast in the form of insoluble uranium-phosphate complexes. 

The idea behind the importance of these genes is that yeast deals with higher uranium levels by scavenging more phosphate.  When genes involved in this process are knocked out, the yeast can’t get the extra phosphate it needs to form the insoluble uranium phosphate complexes.  Now it grows poorly and has less uranium on its surface. 

It will be interesting to see how the other genes are involved in uranium survival or accumulation.  Perhaps one day researchers will be able to turn yeast into a grade A uranium sponge.  Here’s hoping they can!

For those really interested, here is a list of the genes identified in each screen:

Uranium sensitive: PHO2, PHO84, PHO86, PHO87, VPS74, ENT5, CPR1, GLO2, OPI1, ATG15, PTC6, SLC1, and uncharacterized ORF, YPR116W.

Uranium accumulation: OPI1, PHO86, APL4, PEX10, VPS74, PHO2, SPT20, GAL11, SWP82, IVY1, FLO1, DIT2, RPL2A, and uncharacterized ORFs, YGL214W, YJR098C, YNL035C, and YPR116W.       

A nice lecture on bioremediation (using biology to clean up toxic waste)

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