How cool is this link my friend and colleague Luis Zaman sent out:
“Osborne and Akerboom were hoping for a brewing revelation – an entirely new strain of wild yeast that would shake the brewing industry to its core and open up a whole new world of possibilities for craft brews. What they discovered turns out not to be an entirely new species, but rather a new subspecies of the yeast well known to breweries and wineries worldwide: Saccharomyces cerevisiae. They’re calling the new variant Saccharomyces cerevisiae var protocetus after the protocetid whale fossil it was swabbed from.”
That’s right. They cultivated their yeast from a fucking petrified whale skull. Well, I’ll drink it (ed. note, ASD will drink pretty much anything), but it might not be as awesomely unique as it sounds. When I saw the headline, I was expecting to read about actual fossil yeast, like for instance something cultured from an urn in an ancient Egyptian brewer’s tomb. But no, they’re just swabbing fossil bones — which means they’re just culturing normal, modern wild yeast that happen to be hanging around in museum vaults or in the soils where the fossils were discovered. Ask any brewer about beers made from wild yeasts — or better yet, sample a lambic or a sour ale for yourself. Brettanomyces is a common wild strain, and has a reputation for tasting like black pepper or band-aids, depending on who you talk to.
Brett and other wild yeasts are very popular with the “cool beer” kids because of their wildly funky flavors, contributed by the variety of “secondary metabolites” they produce. But why do the wild yeasts produce more secondary metabolites than the domestic Saccharomyces cerevisiae we’re more familiar with?
The term “secondary metabolite” tells the story. To the yeast, there’s nothing “secondary” about these flavorful products. They make them for important physiological reasons — sometimes as antioxidants, sometimes as opportunistic electron acceptors during fermentation, or for any number of other functions. We call them “secondary” because all we care about is achieving the highest efficiency yield of the “primary product” which is good old ethanol.
Over the millenia that humans have been intentionally fermenting sugars, traits have been selected that favor increased yield of ethanol. The easiest way for a cell to make more of one product is to make less of another one — hence selection for more booze means fewer “secondary” metabolites. This is an example of “artificial selection” and is similar to the production of domestic cattle and grossly exaggerated seed size in maize (i.e., ears of corn), and those absurdly big-breasted roaster chickens you find at the supermarket.
Careful thinking about artificial selection was one of several elements that led Darwin down the path to his theory of natural selection. Today, many of us engage in a more academic form of artificial selection — experimental laboratory evolution — which largely involves transferring microbes from one culture to a fresh one over and over and over, and observing what sorts of mutations arise as the microbes adapt to the environment where we raise them. We’ve been able to use this method to directly test the mathematical predictions of evolutionary theory, and it’s even yielded unexpected insights into the nature of the evolutionary process itself, as well as the evolution of novel complex traits. All in all, experimental evolution is “gee whiz” science at its best, and I thank the gods (and my funding agencies, NASA and NSF — love you guys) that I get paid to be a part of this kind of thing.
But even before I got my hands dirty at the bench, it occurred to me that brewers have been using the exact same methods for thousands of years. While brewers must have understood that fermentation was caused by some sort of living, growing thing, it wasn’t until the great microbiologist Louis Pasteur started investigating the pathogenesis of beer souring that it was understood that yeast was a microbe. Even then, the isolation of pure cultures had to await Robert Koch’s fortuitous observation of bacterial colonies growing on a decaying potato. So, almost every batch of alcohol produced for the first 5,000 years of the brewer’s craft was produced by transferring yeast from a previous batch.
The implications of this transfer process go far beyond what we normally think of as artificial selection, and are a perfect illustration of why evolution looks different to microbes than it does to “charismatic macrofauna” like ourselves. One of the most important factors determining how evolution affects a species is population size: the larger the population, the easier it is for natural selection to work. Imagine that the critters are playing the lottery trying to find a “winning ticket” mutation — the more chances they have to draw a number, the more likely they are to win.
When humans were selecting cattle, or corn, or big chicken boobs, we were working with extremely small population sizes — just the animals we kept in our farms, maybe a few hundred individuals. And when we picked the best and brightest of our charges to breed, the effective population size dropped to 2 individuals — the mating pair. Thus, the only selection that could happen was what the humans intended.
But think about yeast — in a single 5-gallon batch of homebrewed beer, there are roughly 1013 yeast cells — that’s 10 million million individuals. Even if only 1 in 1000 of those cells is transferred to the next batch, we’re talking about a population size greater than the entire human race. Prior to the ability to select a single yeast “clone” using Koch’s method of colony isolation, we weren’t able to pick single yeast individuals to breed, so our ability to pick the best strains was limited at best. And because of the great population sizes, the yeast were evolving on their own the entire time as well.
The homebrewer knows the results well — dozens of unique yeast strains, cultivated throughout the European diaspora (and beyond), each with distinct flavor profiles and growth characteristics. Some float, some sink; some leave cloudy beer, some form a thick skin at the surface; some like the cold, and some prefer warmer temperatures. Some ferment “clean” and some leave lots of fruity secondary metabolites. Almost none of these traits have been intentionally selected, although modern techniques have allowed the development of spectacular workhorse strains like the monster used to produce Samuel Adams’ Utopias. No — the delicious diversity of modern beer and wine is the result of good old-fashioned natural (not artificial) selection, caused by massive populations of yeast adapting to the unique environments of breweries in Belgium, Germany, Britain, Russia, France, Italy, etc, etc, etc….
So I’ll drink the whale-bone beer — but if you want to taste evolution, really, any beer will do.