Discovering Biology in a Digital World

What are the advantages of using yeast and working on this kind of problem?

• This could have a socially beneficial result. Contamination of soils, water, and even toys with heavy metals like lead, arsenic, and others, is a growing problem. If DIY biologists could make a cheap test, it could be helpful for a large number of people.
• Yeast, at least the ones I'm thinking about, Saccharomyces cerevisiae, are not pathogens and the GFP protein isn't harmful. If we can sell fish with GFP at Walmart, brewer's yeast with GFP shouldn't be anything of environmental threat.
• You can use amino acids to select the engineered yeast, thus avoiding issues with antibiotic resistance genes.
• Yeast are easy to store and easy to ship. I regularly buy dried packets of yeast at the grocery store
• There are some existing examples for doing this. Mike Barnkob pointed me to a wonderful example yesterday from the IGEM competition where the 2006 University of Edinburgh IGEM team made sensors for arsenic.

How would I go about doing this?

The Edinburgh arsenic project shows what can be done with this kind of system. For a proof of concept project, it might be best to make the sensor digital. That is, have the yeast provide a "yes" or "no" answer at first, and later work on tweaking the system to make it more quantitative.

This could be done by putting a green fluorescent protein gene (GFP) under control of the yeast metallothinein promoter as I've outlined below. The idea is that, in the presence of a heavy metal, the yeast will glow under a black light.

Here's what the yeast look like when they're making GFP:

What are the disadvantages of this method?

• We need a bit more information. Unfortunately, in the papers I read, it looked like the transcription factors that activate the metallothinein promoter are best characterized in terms of binding to copper (1). I know metallothinein expression can be turned on in mammalian cells by cadmium, arsenic, and other metals, but I'm not sure about yeast. It might be okay to have an all purpose metal sensor, but this requires more literature research.
• It's harder to get DNA into yeast than into E. coli
• If you really wanted to test this, you need to find some heavy metals or contaminated soil. I think for a proof of concept test, though, you could spread some yeast on a penny and see if that makes it light up.

Reference:
1. Keller, G., Bird, A., and R. Winge. November 2005. Independent Metalloregulation of Ace1 and Mac1 in Saccharomyces cerevisiae. Eucaryotic Cell 4:1863-1871.