Yeast proteostasis Posted on 10/26/2019 12:56:36 PM PDT by LibWhacker
One of the oldest and most successful human endeavors is the fermentation of cereal-based mush to create an ethanol-rich liquid. In other words, beer-making.
At the heart of this process is yeast, a single-celled fungus that does all the heavy lifting for brewers. It is so important that beer makers have learned to collect the yeast from the fermented liquid and reuse it in the next round. This trick, called “serial repitching,” saves both time and money.
However, after several generations, the quality of the yeast begins to drop. This impairs fermentation and introduces off flavors that ruin the beer.
But why? The problem with serial repitching has beer makers and cell biologists scratching their heads. Clearly, something about the fermentation process is making new generations of yeast less able to ferment. But what?
Today, we get some interesting thoughts on this topic from Bianca Telini and colleagues at the Brewing Yeast Research Group at the Federal University of Rio Grande do Sul in Brazil. They say that ethanol itself may be responsible for the change, because in high concentrations it creates a kind of stress for yeast cells that changes the way their molecular machinery works. And they say a better understanding of this process could help make beer better for all of us.
First some background. Cell biologists have long known that fermentation dies down as ethanol concentration increases. That’s why fermentation cannot produce liquids with an alcohol content higher than about 20%.
Ethanol kills yeast in high enough concentrations. But beer making occurs at significantly lower concentrations, where ethanol merely stresses the cells, much in the way that elevated temperatures do.
One theory of why yeast becomes less effective over generations of serial repitching is that fermentation selects yeasts that are more tolerant to ethanol, and these are also somehow lower in quality.
The problem with this theory is that the evidence doesn’t support it. In 2007, researchers searched for genetic changes in ale yeast involved in serial repitching over an entire year. But after 98 generations, they found no evidence of genetic changes in the yeast at all. The yeast descendants were genetically identical to their ancestors.
So if the yeast isn’t “evolving,” something else must be responsible for the impaired fermentation. The question is what.
Over the millennia, organisms have evolved various complex biochemical mechanisms to cope with factors that stress them. For example, plant cells (and other cells) react to elevated temperatures with what’s known as heat shock response. The study of this response has become an area of intense research for scientists hoping to develop crops capable of flourishing in warmer climates.
What they have discovered is that heat shock response causes the cell to start making molecular machines called chaperones that help combat the effects of higher temperatures. Heat tends to change the shape of proteins and, therefore, their function. Chaperones mitigate this process by preventing or reversing protein misfolding.
Yeast proteostasis
Heat shock response is a complex process because cells are capable of making thousands of different proteins. But only a subset of these proteins are expressed at any one instant, and the subsets differ inside each organelle in the cell.
So maintaining the function of these proteins—proteostasis—requires a complex signaling mechanism that switches on the relevant genes in each organelle. This switching process must be coordinated across the cell, since organelles depend on each other.
The process of communication and coordination is called cross-organelle response, or CORE, and it is poorly understood. But this is an important emerging area of cell biology: biologists are beginning to realize that CORE plays a crucial role not just in heat shock response but in metabolism in general, and even in processes such as aging.
The key idea that Telini and co explore is that ethanol induces a process similar to heat shock, and that this “ethanol shock response” must also be closely linked to CORE. They hypothesize that this somehow reduces the vitality of yeast cells during serial repitching. But exactly how isn’t yet clear.
One possibility is beginning to emerge. The molecular chaperones in yeast help ensure that proteins fold in the correct shape. But this can lead to structural changes in the genome itself. So a high ethanol concentration doesn’t change the genetic code or the phenotype of yeast, but it can change the shape of the genome and consequently the way it functions.
Yeast organisms that are recycled during serial repitching live in an alcoholic world—they are literally swimming in alcohol. In fact, they and their descendants live their entire lives under a level of alcoholic stress that triggers a constant shock-like response.
That means the cells are full of chaperones working overtime to maintain protein function. The new theory is that this inevitably lowers the vitality of the yeast. Indeed, researchers have found that yeast kept in high levels of ethanol in the lab eventually show changes in the structure of their genome. They have the same genetic code, but the DNA is packed in a different shape. In the lab, this becomes evident after more than 250 generations.
Exactly how this happens isn’t known. Neither is it clear why it should become significant after a large number of generations but not before. “The impact of this mechanism remains to be determined in beer fermentation,” say Telini and co.
But that raises important questions for cell biologists to get their teeth into. It might even give us a handle on other mysterious processes such as aging. Hence Telini and co’s interest: “A better understanding of the CORE network in the context of beer fermentation and/or ethanol stress will allow us to improve different aspects of brewing, which will ultimately improve beer yield and quality.”
And who doesn’t want that!
Huge topic. The control of chaperones has implications for anti-mutagenic applications such as cancer research. I’ve said it many times before: beer will save humanity!
“I’ve said it many times before: beer will save humanity!”
Have you seen the History of Beer’ on History channel? Without beer, there would be no America. The American Revolution was “fermented” in colonial beer halls where colonials either troll Brit soldiers or have meetings in them on how to screw the limeys..
I love it. It's gonna be glorious!
It doesn't take a Sherlock Holmes to recognize that a 0.07% solution has got to be less stressful than a Seven-Per-Cent Solution.
(See what I did there?)
” I’ve said it many times before: beer will save humanity!”
Thank you for saying that...many times.
I made beer for 15 years back when I started when I was 17 I taught six people to brew beer that started major breweries and made millions at it
all my beers were 12 to 15% alcohol because I simply took the ingredients and doubled them
my ex-wife made me quit about 2001 and the funny thing is I really only like IPAs now whereas back then I used to brew Stout porters and barley wines
The amazing thing is you’re allowed to own all of the beer bring equipment and bring your own beer at age 16 I found that out when I was at Berkeley and I was only 17
I was a pretty famous camper there at my co-op in Berkeley in the 1980s with my super Duper beers
there was really only Sierra Nevada’s back then
“It doesn’t take a Sherlock Holmes to recognize that a 0.07% solution has got to be less stressful than a Seven-Per-Cent Solution. “
That’s how the cultures are made for home brewers.
The yeast actually grows to its greatest extent over about 48hrs. Once it saturates the brew, conversion to alcohol starts.
Taking a sample somewhere between 24 and 48hrs would provide a robust density of robust yeast.
Seems to me that every couple of beer batches, they need to do a few “yeast generations” without forcing the yeast organisms to generate alcohol. Give’em a chance to “rest up” so to speak.
Ah! I guessed another one right!
Happy with Hamm’s here. Looking for Blatz.
Anchor Steam predates Sierra Nevada by a HUGE number of years.
Quite so. True for cocaine AND alcohol...
There is a bakery here that has a thriving 150-year-old yeast colony that they brought from Germany, and they make the singular best donuts and bread you have ever tasted.
The amazing thing is you’re allowed to own all of the beer bring equipment and bring your own beer at age 16 I found that out when I was at Berkeley and I was only 17
I was a pretty famous camper there at my co-op in Berkeley in the 1980s with my super Duper beers
there was really only Sierra Nevada’s back then
What is a "Sierra Nevada"?
.
.
Glug! Glug!
This is also interesting because I remember a study of resveratrol - which was going to make us all live forever about 5 years ago - concluded that the highest commercially-available resveratrol-laden vino was some Finger Lakes red (was it a Pinot?) that the grape strain had consistently undergone the most stress from both climate maxima and pathogens (mold, etc.); and yet always flourished year-to-year.
If you could remember how to do that, I wonder if a brewery could use that as a starting point for creating the currently commercially-popular flavored beers, rather than utilizing a shitty, plain malt base.
This is fairly predictable, but raises interesting questions about how alcohol could be affecting human beings. Anything that substantially alters cellular metabolism can eventually cause epigenetic changes that alter gene expression - and thus alter biology. Alcohol has lots of effects on metabolism - and it would not be surprising in the least that chronic recurrent alcohol exposure could alter epigenetic programming.
Making beer is easy, storing it is the problem.
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