Chris Todd Hittinger: Centuries old beer yeast mystery solved!
Christopher Todd Hittinger, Assistant Professor
Department of Genetics
UW-Madison College of Agricultural and Life Sciences
cthittinger@wisc.edu
(608) 890-2586
The tale of the lost larger beer yeast
8:16 – Total Time
0:20 – The importance of the larger beer yeast discovery
1:00 – Unique nature of the yeast
1:23 – How the yeast traveled
2:02 – What the discovery may mean
3:08 – Changes in the yeast with time
4:24 – How the ancient brewers used the yeast
5:17 – How the yeast was discovered
6:21 – Where Saccharomyces eubayanus was found
7:10 – What it felt like to make the discovery
8:07 – Lead out
TRANSCRIPT
The history of a beer making yeast is now uncovered. We’re visiting today with Chris Todd Hittinger, Department of Genetics, University of Wisconsin, in the College of Agricultural and Life Sciences, Madison, Wisconsin and I’m Sevie Kenyon.
Sevie Kenyon: Chris, welcome to our microphone. Chris, why was the investigation in the history of this particular yeast so important?
Chris Todd Hittinger: Well, people have been looking for the missing component of lager yeast for a long time and this has been something of an historical curiosity. We’ve known that it is a hybrid of the ale yeast, Saccharomyces cerevisiae, with some missing component that nobody had been able to find in either natural or industrial environments in Europe. We and [our] collaborators have set about sampling Saccharomyces, the genus, from all over the world. And we’ve sampled five different continents and it turns out in Patagonia we finally found a wild species that matches the genome that matches the genetic code of lager yeast.
Sevie Kenyon: What’s so unique about the yeast you’ve uncovered?
Chris Todd Hittinger: Traditional ale strains prefer much warmer temperatures, and so when Bavarians began the lagering process in the 1400s, of brewing and storing their beer in cellars and caves this created a situation where the ale yeasts were not optimal to brewing at these colder temperatures.
Sevie Kenyon: Can you give us a sense for how this yeast got from Argentina to Bavaria?
Chris Todd Hittinger: We know that Saccharomyces yeasts like rotting fruit. With the rise of trans-Atlantic trade in the 1500s there would have been a lot of fruit and other agricultural products, and indeed, fermented beverages going back and forth and Saccharomyces eubayanus would have been happy on any one of these substrates. These yeasts are also found in the digestive tracts of fruit flies and other insects, which would have also been hanging out on agricultural products and also on these ships. It’s really any number of ways that trans-Atlantic trade could have provided a fairly efficient route from Patagonia into Europe.
Sevie Kenyon: Chris, can you give us a sense as to what comes after this discovery?
Chris Todd Hittinger: Well there are a few exciting possibilities; one is the original motivation for this study, is to sketch out the biodiversity of this important genus. And we are really, now, applying these genomic tools to understand what makes one yeast different from another yeast. And these are exactly the kind of tools that you’re going to use in your doctor’s office five, ten and twenty years from now as you go in to understand what makes one human different from another. And, the other application is perhaps a little more fun and that is the understanding the genetic basis of the yeast strains that people use for different brewing strains.
And you can image, as we collect half a dozen or a dozen or even hundreds of genetic changes that we know confer specific changes in yeast, you can image the brewing industry going in and possibly selecting and making designer yeast based on subsets of traits. I certainly hope that in the future we will be able to consume designer products.
Sevie Kenyon: Chris, some change took place when this yeast traveled between continents. Can you give us an idea what that looked like?
Chris Todd Hittinger: The yeast exits as a diploid organism, meaning that it got one copy from its mom and one copy from its dad, although it’s yeast, so we call it A and alpha instead. These species will mate with other species. All that has to happen is [you have] an A spoor from one species and an alpha spoor from another. So as soon as eubayanus came on the scene in Europe and produced spoors, it would have been able to very quickly hybridize with the existing ale strains. Once that hybrid forms, it’s sterile, much like a mule, a cross between a donkey and a horse. So, it can’t then reproduce with any of the other wild yeasts, but it is able to reproduce indefinitely, asexually, especially when it’s in this sugar-rich environment and being actively passaged by brewers from one batch to the next. During that time, this also created a situation where new mutations could be selected for and we actually map out a few differences between this hybrid that would have occurred after this hybridization event and these are genetic changes that occurred during the domestication process and were selected for either by the competitive brewing environment itself or possibly by brewers interested in particular outcomes.
Sevie Kenyon: To speculate, when the brewers first realized they had something special or different going on?
Chris Todd Hittinger: In the mid 16th century, there was a law passed in Bavaria that banned brewing beer during the summer because it was of inferior quality and since lagering had begun in the 1400s it’s possible that by the mid 1500s they had realized that there was definitely a distinctive product with particular qualities. Now whether these eubayanus – cerevisiae hybrids were related to that change or not, we certainly can’t say. The trans-Atlantic trade didn’t really get going until the late 1400s. It seems likely that the process itself of lagering probably preceded the arrival of eubayanus, but this actually is not that uncommon in most evolutionary instances you see an ecological niche open up before it can be exploited by the importers.
Sevie Kenyon: Chris, can you describe for us this worldwide sampling process for yeast?
Chris Todd Hittinger: Our five continent survey has been headed up by our senior author Jose Paulo SamPiao in Portugal. He’s developed a quite reliable protocol of sampling for saccharomyces yeast. Said, involves scrapping bark or soil, or even in the case of this new discovery, galls from trees. Bringing them back in the lab, growing them with antibiotics to kill the bacteria and also growing them with high levels of sugar and alcohol. And with a fair amount of regularity you can get saccharomyces or other yeasts that are similar to them. Then we can use some crude genetic techniques to sketch out approximately what they are and when we think we’ve found something interesting, that’s when we bring in the whole genome sequencing and determine the complete genetic makeup and compare that to known strains and that’s exactly what we’ve done here to clarify that this is a new species, distinct from all previously discovered species and wild and that it is a 99.5 percent match to the missing component of the lager genome.
Sevie Kenyon: Chris, can you describe for us where this yeast was found?
Chris Todd Hittinger: In Patagonia, there are a family of southern beech trees. These trees will get infected by a parasitic fungus and will form these sugar-rich galls, as the trees try to sequester off this infection. The native peoples of Argentina would actually harvest these galls and make primitive fermented beverages out of these, by mixing it with water. They’ll still actually consume these galls in salad. Because we knew that there were the deeper sugar-rich habitats and that people had been fermenting them, this was a prime candidate to look for saccharomyces yeasts. Our collaborator, Diego Libkind, in Argentina, was actually the one who made the original isolation and discovery.
Sevie Kenyon: Can you describe for me what it felt like when you knew you had something unique here?
Chris Todd Hittinger: Yeah, so I remember the first time we got a peek at the genome of this strain and of several of the other brewing strains. My post-doctoral adviser and Jim Dover who did some of the technical aspects of the sequencing and I, actually did gather over lagers and ales to go over the initial raw data. And, it turned out to be a surprisingly clear and lucid presentation, because the data was so clear. Post-doctoral advisor Mark Johnston and I have had a long-standing, friendly disagreement about the relative merits of ales and lagers and neither of us has changed our opinions on that. He is an ale man and I am a lager man. And I think as data started to come in, we certainly both have a much greater appreciation for the complex processes that have given rise to the lager beers that many of us enjoy today
Sevie Kenyon: We’ve been visiting today with Chris Todd Hittinger, Department of Genetics, University of Wisconsin, in the College of Agricultural and Life Sciences, Madison, Wisconsin and I’m Sevie Kenyon.