Researchers at the University of Wisconsin-Madison have developed a simple, robust, and efficient method for generating interspecies yeast hybrids. As reported in the journal Fungal Genetics and Biology, this method provides an efficient means for producing novel synthetic hybrids for beverage and biofuel production, as well as for constructing tetraploids to be used for basic research in evolutionary genetics and genome stability.
Some 500 years ago, the accidental natural hybridization of Saccharomyces cerevisiae—the yeast responsible for things like ale, wine and bread—and a distant yeast cousin gave rise to lager beer. Today, cold-brewed lager is the world’s most consumed alcoholic beverage, fueling an industry with annual sales of more than $250 billion.
The first lagers depended on that serendipitous cross of Saccharomyces species as evolutionarily diverse as humans and chickens. The result, however, yielded a product of enormous economic value, demonstrating the latent potential of interspecies yeast hybrids. In nature, the odds of a similar hybridization event are, conservatively, one in a billion.
We can achieve hybrids at rates of one in a thousand cells. It is much more efficient than nature.—William Alexander, lead author
There are hundreds of known species of yeasts and they occupy almost every ecological niche imaginable worldwide. They are essential to the process of fermentation, where the microbes convert sugars to alcohol and carbon dioxide. Yeasts are used widely to not only make beer, wine and bread, but also cider, whiskey, cheese, yogurt, soy sauce and an array of other fermented foods and beverages. In industry, yeasts are used to produce biofuels and to make enzymes, flavors and pigments and even drugs such as human insulin.
An ability to quickly and efficiently churn out new yeast interspecies hybrids means industries that depend on yeasts will have many more organisms to experiment with to make new flavors, enhance production and produce entirely new products, explains Chris Todd Hittinger, a UW-Madison professor of genetics and the senior author of the new study. Hittinger is a world authority on yeast genetics and a co-discoverer of the wild Patagonian yeast that formed the lager beer hybrid.
For example, the marriage of Saccharomyces cerevisiae and its distant cousin Saccharomyces eubayanus, a species that inhabits tree galls in nature, permitted the cold-temperature fermentation that made lager beer possible.
The new yeast hybridization method uses plasmids, circles of DNA that can be built into an organism to confer a genetic quality. In the lab, plasmids are routinely used to manipulate genes in cells. Genes in the plasmids facilitate yeast hybridization by expressing a naturally occurring yeast protein that allows two distinct species of yeasts to mate.
The plasmids used to facilitate the process of hybridization can be removed from the new hybrid yeasts, leaving the genomes of the two fused organisms unchanged.
The advantages of the technique are speed, efficiency, and precision. Within a week, you can generate a large number of hybrids of whatever two species you want, creating forms never seen before.—Chris Todd Hittinger
The new study describes four new hybrids, one of which was made using a strain of Saccharomyces eubayanus discovered near Sheboygan, Wis., after Hittinger and his colleagues first found the lager yeast parent in the alpine regions of Patagonia. The new hybrid is being tested in a new beer recipe in the UW-Madison Department of Food Science.
The new technique may also help industry overcome a creative bottleneck, as many industrial strains of yeasts are sterile, unable to produce spores.
The new study was supported by grants from the National Science Foundation and the Department of Energy through the Great Lakes Bioenergy Research Center.
William G. Alexander, David Peris, Brandon T. Pfannenstiel, Dana A. Opulente, Meihua Kuang, Chris Todd Hittinger (2015) “Efficient engineering of marker-free synthetic allotetraploids of Saccharomyces,” Fungal Genetics and Biology doi: 10.1016/j.fgb.2015.11.002