To begin to understand the outsized potential and sheer weirdness of yeast, it helps to consider the genetics behind one of the world’s most successful and useful microorganisms. It also helps to consider lager.
Lager, or cold-brewed beer, is made possible by the union of two distinct species of yeast. About 500 years ago, these two species, Saccharomyces eubayanus and Saccharomyces cerevisiae, joined in a Bavarian cellar. They gave us a hybrid organism that today underpins an annual global market for lager estimated at one-quarter of a trillion dollars.
“We would not have lager if there hadn’t been a union equivalent to the marriage of humans and chickens,” notes Chris Todd Hittinger PhD’07, a CALS professor of genetics and a co-discoverer of S. eubayanus, the long-sought wild species of yeast that combined with the bread- and wine-making S. cerevisiae to form the beer. “That’s just one product brewed by one interspecies hybrid.”
Yeasts, of course, are central to many things that people depend on, and the widespread domestication in antiquity of S. cerevisiae is considered pivotal to the development of human societies. Bread and wine, in addition to beer, are the obvious fruits of taming the onecelled fungi that give us life’s basics. But various strains and species of yeasts also are partly responsible for cheese, yogurt, sausage, sauerkraut, kimchi, whiskey, cider, sake, soy sauce and a host of other fermented foods and beverages.
Baker’s yeast, according to yeast biologist Michael Culbertson, an emeritus professor and former chair of UW– Madison’s Laboratory of Genetics, ranks as “one of the most important organisms in human history. Leavened bread came from yeast 5,000 years ago.”
Beyond the table, the microbes and their power to ferment have wide-ranging applications, including in agriculture for biocontrol and remediation, as well as for animal feed and fodder. They are also widely used to make industrial biochemicals such as enzymes, flavors and pigments.
What’s more, yeasts are used to degrade chemical pollutants and are employed in various stages of drug discovery and production. Human insulin, for instance, is made with yeast. By inserting the human gene responsible for producing insulin into yeast, the human variant of the hormone is pumped out in quantity, supplanting the less effective bovine form of insulin used previously.
Transforming corn and other feedstocks, such as woody plant matter and agricultural waste, to the biofuel ethanol requires yeast. Hittinger is exploring the application of yeast to that problem through the prism of the Great Lakes Bioenergy Research Center (GLBRC), a Department of Energy-funded partnership between UW–Madison and Michigan State University. Hittinger leads a GLBRC “Yeast BiodesignTeam,” which is probing biofuel applications for interspecies hybrids as well as genome engineering approaches to refine biofuel production using yeasts.
“There are lots and lots of different kinds of yeasts,” explains Hittinger. “Yeasts and fungi have been around since Precambrian time—hundreds of millions of years, for certain. We encounter them every day. They’re all around us and even inside us. They inhabit every continent, including Antarctica. Yeasts fill scores of ecological niches.”
The wild lager beer parent, S. eubayanus, for example, was found after a worldwide search in the sugarrich environment of Patagonian beech trees—or, more specifically, in growths, called “galls,” bulging from them. (How S. eubayanus got to Bavaria hundreds of years ago and made the lager hybrid possible remains a mystery.) It is possible, notes Hittinger, to actually smell the S. eubayanus yeast at work, churning alcohol from the sugars in the galls themselves.
Continue reading this story in the Spring 2015 issue of Grow magazine.