Alcohol School moves to the lab, addresses yeast modification

By Lisa Gibson | September 11, 2019

Emily Stonehouse, research and development manager for Mascoma LLC, told her audience at the Alcohol School Sept. 11 that she considers herself a “yeast mechanic.” Yeast is an important substance, she said, used to produce more than 80 percent of renewable fuels globally, as well as food, beverages, vaccines, pharmaceuticals, chemicals, proteins and more.

Lallemand Biofuels & Distilled Spirits’ Alcohol School is being held Sept. 9-13 at Intercontinental Montreal in Montreal, Quebec. The sessions Sept. 11 were held at National Research Council Canada, with tours of Lallemand’s research lab spaces on site. Mascoma is the research arm of Lallemand.

Stonehouse explained that the “holy grail” of yeast is to find a naturally occurring strain that possesses the desired traits. “But it’s a lot of work,” she said.

So, Stonehouse discussed two methods to craft yeast with desired traits: classical genetics and genetic engineering. Through classical genetics, no DNA is added from outside the cell. Instead, it uses other tactics such as mating, hybridization, protoplast fusion and mutagenesis. While it’s not considered genetic engineering, classical genetics is time-intensive, is not precise and can result in unintended mutations.

With genetic engineering, DNA is added, Stonehouse explained. First, a trait is identified, and the gene sequencing is obtained. The genes are then synthesized, the yeast is designed and built, the DNA is transformed into yeast, and it’s integrated onto yeast chromosomes. “The benefit of genetic engineering is it’s really precise,” Stonehouse said. “You built what you wanted to build.”

Genetic engineering is also extremely fast, but it’s regulated and carries a negative consumer perception, she added.

Still, genetically engineered yeast has been used for years in many applications, and about 70 percent of U.S. and Canadian ethanol plants use it to improve tolerance to inhibitors, reduce fermentation byproducts and prompt the yeast to excrete enzymes like glucoamylase, Stonehouse said. In 2012, Lallemand introduced the first commercially available glucoamylase-expressing yeast, TransFerm. Now in its Y3 from, TransFerm has continually been innovated, Stonehouse told her audience.

Mascoma has also been developing yeast strains for sugarcane ethanol in Brazil. Those strains need to be recycled with acid for a 200-day crushing session, and withstand two to three fermentations per day, each six to 10 hours long, Stonehouse said. Brazil’s process also does not use added enzymes.

The SucraMax strain has achieved those goals, she said, reducing glycerol, increasing ethanol yield and reducing yeast biomass. Continued improvement of SucraMax will include increased persistent time in the recycle process, further increased ethanol yield, and added value to the large volume of biomass produced.

Stonehouse referred to a colleague’s presentation for more information about cellulosic ethanol yeast strains, but said, “Genetically engineered yeast strains are essential for cellulosic ethanol.”