Other kinds of nerds have discovered what beer geeks have known for a long time: Brewers yeast is an amazing little critter. In the world of brewing, yeast is a major factor in the character and potency of a beer. In the world of science, it is an industrious single-cell organism that is sometimes called upon to help humans unravel the underpinnings of life on Earth.
The most recent example of this comes from the University of Minnesota, where a couple of experimental evolution geeks (Post doc researcher William Ratcliff and his adviser Michael Travisano) were trying to figure out the coolest thing they could do in their lab. They didn’t have the resources to play around with the origins of life, so they decided the next best alternative was to explore the origins of multicellular life.
Multicellular life isn’t a simple thing to create. It took our primordial ancestors about three billion years to evolve from single-cell organisms, and billions more to morph into the collection of 100 trillion cells (with over 200 varieties working in concert) that makes up today’s average web-surfing American. Of course with all the brain cells we burn on cable TV and alcohol, our cell count is probably closer to 90 trillion, but I digress. 🙂
Ratcliff and Travisano weren’t looking to create anything as complex as a human. Instead, they aimed to create primitive multicellular creatures, and decided brewers yeast was great place to start. Brewers yeast lives a simple existence – it floats in fluid, eating sugar and budding off daughter cells who float away and in turn do the same thing.
Ratcliff and Travisano placed brewers yeast in flasks full of broth, which were shaken for a day and allowed to settle. They then extracted a small sample of yeast from the bottom of the flask and put it in a fresh broth and repeated this process again and again.
By doing this, they isolated the cells that dropped the quickest, favoring the cells that were the most dense. After a couple of weeks, they noticed that the yeast was sinking very fast and forming a cloudy layer at the bottom of the flasks. When they looked at it under the microscope, they were greeted with snowflake-shaped clusters of multicellular yeast. This wasn’t that a bunch of single-cell critters that were stuck together – these were bonafide multicellular organisms, each with hundreds of cells. Brewers yeast managed to accomplish in a couple of weeks what took our single-cell ancestors billions of years to do.
When one of these cells was plucked off the organism and allowed to reproduce, its babies went right about the business of forming clusters of cells. This showed that the organism had indeed mutated into a multicellular creature. When allowed to grow to adulthood (which takes just a few hours), these new multicellular organisms would expand the arms of their snowflakes until they pressed together, breaking one away, which would then form into its own snowflake and repeat the process.
Ratcliff tells the New York Times that “Forming clusters isn’t a freaky yeast thing.” It is the way that many animals and plants began their climb to what we see today, so this is indeed a peek at how multicellular life got its start, with single cell organisms mutating through the process of natural selection. In the case of this brewers yeast, the survivors were the critters at the bottom of the flask, in nature it was the ones who best responded to their environment and propagated successfully.
Ratcliff and company are still playing around with the evolution of yeast cells, but won’t say where they’re headed until they publish their results. All Ratcliff would tell the Times is that, “We’re getting really interesting things happening now.”
This got me to thinking about what might be happening in the two carboys full of homebrew that have been sitting in my master bathroom tub for several months. If Ratcliff and his colleagues got multicellular organisms to form a couple of weeks, I imagine by now my beer has opposable thumbs!