In Wisconsin, researchers from the University of Wisconsin–Madison and several Department of Energy laboratories identified two changes to a single gene that can make yeast tolerate pretreatment chemicals during biofuel production.
The toxicity involved in pretreatment chemicals is enough to make the yeast as much as 70 percent less efficient at turning sugar into biofuel, a crippling loss for an industrial process. But researchers looked at 136 yeast isolates and found one strain with outstanding tolerance to ionic liquids. They screened DNA sequences from this strain and identified a pair of genes key to surviving the otherwise toxic pretreatment chemicals. One of the genes, called SGE1, makes a protein that settles in the yeast cell membrane and works as a pump to remove toxins.
A change of just two individual nucleotides among more than 12 million that make up the yeast genome are enough to increase the production of those cellular pumps and protect yeast from ionic liquids. The researchers used the gene-editing tool CRISPR to alter a strain of an ionic liquid-susceptible yeast, introducing the two single-nucleotide changes and successfully producing a yeast that can survive — and ferment — alongside amounts of ionic liquid that are normally toxic.