Genetically engineered yeast soak up heavy metal pollution

July 21, 2017 by Alex Berezow
Credit: American Council on Science and Health

Environmental contamination with heavy metals is often the result of various types of industrial processes. Because heavy metals can be dangerous to humans and other wildlife, contaminated sites need to be cleaned up. This isn't easy. Chemical extraction methods can introduce different types of pollutants into the environment.

Bioremediation—using biological organisms to clean polluted areas—is a hot area of research. Some plants can naturally sop up without any ill effects, but plants don't always grow large enough to soak up all the pollution. Besides, plants can't be used to clean up contaminated water.

So, scientists have increasingly chosen to use the techniques of biotechnology to create genetically engineered microbes capable of gobbling up pollution. The latest example of this was described by a team of Romanian and Norwegian researchers in the journal Applied Microbiology and Biotechnology.

The researchers created new protein-encoding genes that consisted of three parts: (1) A cell membrane anchor; (2) ; and (3) one of three kinds of metal-binding peptides. When these new genes were expressed in Saccharomyces cerevisiae (the common baker's yeast), the new proteins attached to the inner side of the cell membrane and glowed green. (See modified figure. The green glow was necessary for the researchers to verify the location of the proteins in the cell.)

Genetically engineered yeast soak up heavy metal pollution
Credit: Brian Stansberry/Wikipedia

Then, the engineered yeast were tested for their ability to soak up various types of metals. Yeast engineered with a metal-binding peptide made up of aspartate and glutamate were the best at adsorbing copper and ; cysteine peptides were best at adsorbing cadmium and ; and histidine peptides were most adept at adsorbing cobalt and . The best performing strains were able to remove about 80% of their respective metal ions.

The next step, should the authors choose to pursue it, would be to test the engineered yeasts' ability to function in a more useful setting, such as a or an actual contamination site. Also, they will need to determine the best way to harvest (and dispose of) the yeast cells after they have accumulated the toxic metals.

Explore further: Baker's yeast can help plants cope with soil contamination

More information: Lavinia Liliana Ruta et al. Heavy metal accumulation by Saccharomyces cerevisiae cells armed with metal binding hexapeptides targeted to the inner face of the plasma membrane, Applied Microbiology and Biotechnology (2017). DOI: 10.1007/s00253-017-8335-0

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not rated yet Jul 21, 2017
"The next step, should the authors choose to pursue it, would be to test the engineered yeasts' ability to function in a more useful setting, such as a water treatment plant or an actual contamination site. Also, they will need to determine the best way to harvest (and dispose of) the yeast cells after they have accumulated the toxic metals."

Maybe a solution for collection?:

Saccharomyces Cerevisiae is also brewer's yeast. Each beer yeast strain has been modified to give a certain character to the finished beer. One character is flocculation, or the ability of the yeast strain to clump together and settle at the end of fermentation. Natural selection was used to engineer yeasts to floc better to create a clearer product (i.e. yeast cells were collected off the bottom for several generations and the cells that never flocculated were discarded).

Could one do the same with the new GE S. Cerevisiae?.........cont.
not rated yet Jul 21, 2017
Take the genetically engineered yeast, run it in through several generations, skim the bottom cells each time and come up with a better floccing GE strain. Pitch these cells into the polluted area, keep in suspension to do their heavy metals job, add enough glucose to allow the yeast to ferment and settle. Harvest yeast, and associated metals, at the bottom of treatment tank. Byproducts would be ethanol and CO2.

Or do the opposite and GE an already flocculent, readily available strain.

Proteins on the cell surface are one factor in determining the degree of flocculation and since the new proteins in the study are connecting to the cell wall, it may hinder that route.

Some factors involving flocculation include pH of solution, temperature, original gravity, O2 content, yeast pitching rate, and the generation of a strain.

English Ale/London Ale strains are known to be highly flocculent ("1968 London ESB" being one)

Other ways to settle yeast: Colder temps, Gelatin
not rated yet Jul 21, 2017
Lead and arsenic are two of the more common metal contaminates at sites. I wonder how effective this yeast is with those metals and what the cost ratio would be compared to say, excavation/backfill.
not rated yet Jul 23, 2017
I recall that plant remediation presented the same end result. Its collected so what to do with it. The disposal problem remains. It seems that industry wants the same answer that they came up with in disposing of heavy metals in Duff Wilson's book Deadly Harvest. Truck it to a fertilizer plant, add it to the fertilizer, and sell it with the instructions to lime heavily.

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