On Apr. 28, 2020, researchers at the Great Lakes Bioenergy Research Center at the University of Wisconsin-Madison have developed a method to combine traits from up to six different yeast species in a single hybrid strain – a yeast that could carry more tools for a specific job, such as producing biofuels.

Their new method, called iterative hybrid production (iHyPr), allowed the team to produce hybrid yeasts from six different Saccharomyces species. The multi-species hybrids adapted quickly to their environments, making them well suited to laboratory-based evolutionary selection.

“It’s very common to cross different organisms with desirable properties,” such as different varieties of corn or breeds of dogs, says senior author Chris Hittinger, an associate professor of genetics at UW–Madison. “What’s different here is that we’re crossing things that are different species, and are quite distinct genetically.”Two-species hybrids are widely used in agriculture, food and beverage production and other industries. For example, lager beer is produced by a two-species hybrid yeast. A handful of three- and four-species hybrids are known in the beverage industry, Hittinger says, but it isn’t clear how they developed.

But the team used an enzyme that can change one mating-type gene into the other. By changing some a-type cells into alpha-type, the team was able to make crosses that create a mating-ready cell that has two complete sets of chromosomes. Two of these diploid cells from different species could then be mated to create a two-species hybrid with four sets of chromosomes. “Basically, we were hacking the biological system for facilitating crosses of diploids,” Peris explains.

In the new study, the researchers described a way to iterate the method to create even more complex hybrids. So far, they’ve been able to combine the genomes of six yeast species into a single cell. The work is published in Nature Communications.

Combining the method with gene editing tools, such as the CRISPR-Cas9 system, opens the door to creating complex hybrid yeasts with specific sets of desired traits. Hittinger sees many potential research and industrial uses for such hybrids, including studies in genetics, cancer biology, brewing, and bioenergy. The Wisconsin Alumni Research Foundation has filed a patent on the new process.

The team is currently working to produce a hybrid yeast with multiple traits to improve the ability to turn plant material into advanced biofuels, such as isobutanol. One parent is a GLBRC-designed strain engineered with genes that enable it to consume xylose, a sugar found in high levels in biomass but which cannot easily be used by most Saccharomyces strains. But the process of pretreating plant material to prepare it for fermentation can produce toxins that many yeast strains cannot tolerate. With iHyPr, the researchers crossed the xylose-consuming strain with others that are able to grow better under the pretreatment conditions, as well as a strain that can produce high levels of isobutanol.