Crossing yeast strains

So I know very little about yeast biology, but my understanding is that yeast can undergo both asexual (budding) reproduction and sexual (spores combining) reproduction. My understanding is also that yeast in ordinary brewing is almost exclusively budding asexually, so if you blend more than one strain, they will be competing rather than mating. Eventually one strain dominates, and it basically has the properties that strain would have had if you'd just pitched it alone.

What I'm curious about is sexual reproduction.... Is there any way a homebrewer can get two yeast strains to release spores, combine those spores, and therefore produce a hybrid strain? In other words, is there an easy way to induce sexual reproduction in yeast, and to capture the product of that reproduction and step it up for brewing purposes? Also, does this happen to some extent when you blend yeast, or are the strains exclusively budding at that point?

From the PhD Microbiologist on my couch, yeast do not produce sexually "because they are single-cellular organisms." Spore production is asexual reproduction.

http://en.wikipedia.org/wiki/Yeast#Reproduction

So Wikipedia lies?

Sent from my Droid using Home Brew Talk

Ha. She's wrong. I love it.

To answer the other question, yes Wikipedia does lie. Though, not in this case it seems.

Ah yes, I don't doubt that Wikipedia has many a lie lurking uncaught by its vigilante editors. They always seem to undo anything I change, even when I know it was worthwhile (like fixing typos), so I've long since given up on contributing or editing.

So, back to my original question... does anyone know how to induce sexual reproduction in two strains, and control the process well enough to cause them to produce a hybrid strain "offspring"?

Not going to happen, these strains have been so mutated over the years that any sexual reproduction would start you off at square 1. You would terrible yeast charecteristics for many hundred of generations until you refined it enough.

And given the fact that it is not known how Saccaromyces cerevisiae originated (hybridized with wine yeast c. 400 years ago?) you could end up with something not even similar to S. cerevisiae.

theredben said:

Not going to happen, these strains have been so mutated over the years that any sexual reproduction would start you off at square 1. You would terrible yeast charecteristics for many hundred of generations until you refined it enough.

And given the fact that it is not known how Saccaromyces cerevisiae originated (hybridized with wine yeast c. 400 years ago?) you could end up with something not even similar to S. cerevisiae.

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I'm not sure I see how two S. cerevisiae strains, when combined, would be expected to produce anything wildly different from the parent strains. I mean, I would guess that most yeast strains are still fairly closely related, other than a few outliers (that species used in German wheat beers, for example). Also, it seems from what I've read that S. cerevisiae does undergo a sexual reproductive cycle fairly regularly, so wouldn't some minimal degree of cross-breeding be occurring every time you use a blended yeast, like WLP575, for example?

But really the point isn't that I expect the product will be great, but rather I wish to experiment with this process to see what the product will be. My favorite part of brewing is tinkering and trying new things even when they have a decent chance of ending badly.

I would have thought Yeast were only asexual. However I did a google search for 'yeast mitosis meiosis' and found a lot of hits. Like these:

"Using Saccharomyces cerevisiae to study cell cycle genes in meiosis"
Anne Galbraith, Dept of Biology, University of Wisconsin-La Crosse

Finally, although yeast does not look anything like a human, it still grows and divides by the processes of mitosis and meiosis.

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Comparative sensitivity to gamma radiation of yeast mitosis and meiosis
J.J. Millera, V.V. Kingsley*, a and C. Ramirez†, a
aDepartment of Biology and Research Unit for Biochemistry, Biophysics and Molecular Biology, McMaster University, Hamilton, Canada

Induction of meiosis in yeast
A. F. Croes


So there just may be some truth to sex in the fermenter.
My faith in wikipedia has been restored ... for now.

My point is that when dealing with a highly refined asexually propogated organism (many plants, and our faithful brewing yeast) and then allowing sexual reproduction, the genetic transfer will allow it to revert back to some sembelance of that organism's original, uncultivated state. Crossing two strains is going to be impossible unless you have access to equipment to isolate individual cells. Otherwise, just putting two packets of yeast in a flask will inevitably end up with the sexual reproduction happening within the same strain as one will be stressed to the breaking point before the other.

But if you just want to play around, then I say go for it. Do you have access to a quality microscope? If you are going to stress the yeast to it's breaking point you will need some way to assure that what remains when all the haploid cells die off is still Saccaromyces cerevisiae.

Yes, you can induce sexual reproduction in yeast, of course. It's a completely standard part of yeast genetics. It's possible it will be slightly harder in brewing strains, but I doubt it. It will be very difficult (practically speaking, impossible) to do so in any systematic way without a tetrad dissection microscope, and although it can be done in an entirely unsystematic way without one, I can't think of any way you could separate the progeny from the parental strains.

Contrary to what has been said above, there's no reason to think it would "revert" to an "uncultivated" state. That is not (thankfully for the field of genetics) how crosses generally work out.

In summary: Yes, it would be fairly easy given the correct equipment, yes, you'd probably be able to get something like a mixture of the two, but no, it would be very challenging for someone without expensive equipment and a background in microbiology.

Well what I was hoping to get was someone saying "oh, if you put yeast on such-and-such agar, it will induce the yeast to undergo meiosis" or "just add such-and-such chemical to your wort to induce meiosis." The goal then would be to simply streak each strain on separate plates of that type of agar, or wort/agar with whatever additives are necessary, and then to combine the resulting samples in a friendlier environment (regular wort).

I still am confused how two S. cerevisiae strains can possibly produce anything other than an S. cerevisiae offspring. I mean it may be a strain of S. cerevisiae with unfavorable characteristics, but how could two members of the same species produce offspring that is a different species? I mean if you were to cross a chihuahua and a golden retriever, it would undoubtedly be a strange looking dog, but it would still be a dog.

ni* said:

Yes, you can induce sexual reproduction in yeast, of course. It's a completely standard part of yeast genetics. It's possible it will be slightly harder in brewing strains, but I doubt it. It will be very difficult (practically speaking, impossible) to do so in any systematic way without a tetrad dissection microscope, and although it can be done in an entirely unsystematic way without one, I can't think of any way you could separate the progeny from the parental strains.

Contrary to what has been said above, there's no reason to think it would "revert" to an "uncultivated" state. That is not (thankfully for the field of genetics) how crosses generally work out.

In summary: Yes, it would be fairly easy given the correct equipment, yes, you'd probably be able to get something like a mixture of the two, but no, it would be very challenging for someone without expensive equipment and a background in microbiology.

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Ahh thank you -- I posted my other reply before I saw your response. Well, that's more in line with what I was afraid I'd hear when I first posted the question. Yes it can be done, yes it would work, but no, I probably can't do it at home. Ohhh well!

ni* said:

Yes, you can induce sexual reproduction in yeast, of course. It's a completely standard part of yeast genetics. It's possible it will be slightly harder in brewing strains, but I doubt it. It will be very difficult (practically speaking, impossible) to do so in any systematic way without a tetrad dissection microscope, and although it can be done in an entirely unsystematic way without one, I can't think of any way you could separate the progeny from the parental strains.

Contrary to what has been said above, there's no reason to think it would "revert" to an "uncultivated" state. That is not (thankfully for the field of genetics) how crosses generally work out.

In summary: Yes, it would be fairly easy given the correct equipment, yes, you'd probably be able to get something like a mixture of the two, but no, it would be very challenging for someone without expensive equipment and a background in microbiology.

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This has me confused. I have a good working knowledge of microbiology, but a very deep background in botany. In botany, with something like pointsetties which are grown over and over again looking for nice mutations and then asexually propogated until those nice characteristics are set in the genes, you cannot then just let them go to seed and collect that seed for use. The genes will revert back to some unpredictable form with no usefulness. It seems to me that is how it would work with our yeasts, which have been asexually reproduced until the desired mutations have become firmly entrenched in the genetic makeup. Just trying to fully understand this. I am using pointsettias because they are not hybridized which should keep this simpler.

theredben said:

This has me confused. I have a good working knowledge of microbiology, but a very deep background in botany. In botany, with something like pointsetties which are grown over and over again looking for nice mutations and then asexually propogated until those nice characteristics are set in the genes, you cannot then just let them go to seed and collect that seed for use. The genes will revert back to some unpredictable form with no usefulness. It seems to me that is how it would work with our yeasts, which have been asexually reproduced until the desired mutations have become firmly entrenched in the genetic makeup. Just trying to fully understand this. I am using pointsettias because they are not hybridized which should keep this simpler.

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I think that with yeast, your population is billions and billions of times bigger than the population size of your poinsetta. With yeast you're looking for wholesale genetic drift as opposed to a couple useful mutations in a specific individual. They're both examples of artificial selection, but on totally different scales.

winnph said:

Well what I was hoping to get was someone saying "oh, if you put yeast on such-and-such agar, it will induce the yeast to undergo meiosis" or "just add such-and-such chemical to your wort to induce meiosis."

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Sure: "Oh, if you put the yeast on standard presporulation agar, then move it to sporulation agar, it will induce meiosis." Here's a protocol with media recipes (they do their sporulation in liquid media, but it' also easy to do on agar). That exact procedure might not work for some brewing strains, which are sometimes more reluctant to sporulate than lab strains (contrary to the impression I see I gave above -- I ought to proof-read before posting), but something roughly like it would for most strains.

Something a bit easier to try at home might be the induction of (further) polyploidy in brewing strains, although all of the easy ways of doing that involve ludicrously toxic reagents.

bovineblitz said:

I think that with yeast, your population is billions and billions of times bigger than the population size of your poinsetta. With yeast you're looking for wholesale genetic drift as opposed to a couple useful mutations in a specific individual. They're both examples of artificial selection, but on totally different scales.

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Actually, with commercially available yeast (White Labs, Wyeast, et al) they have all been isolated to single cell at some point in the cycle. That is how they have a constitent strain.

theredben said:

This has me confused. I have a good working knowledge of microbiology, but a very deep background in botany. In botany, with something like pointsetties which are grown over and over again looking for nice mutations and then asexually propogated until those nice characteristics are set in the genes, you cannot then just let them go to seed and collect that seed for use. The genes will revert back to some unpredictable form with no usefulness. It seems to me that is how it would work with our yeasts, which have been asexually reproduced until the desired mutations have become firmly entrenched in the genetic makeup. Just trying to fully understand this. I am using pointsettias because they are not hybridized which should keep this simpler.

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Genes do not "revert" (nor do traits get "set in the genes"). Modern poinsettias (there are only two "t"s) are, in fact, hybrids, which is exactly why progeny usually have less desirable traits than parental lines.

@bovineblitz & theredben: The reason I figured there wouldn't be wholesale reversion to primitive properties when you hybridize yeast strains is (using my dog analogy from before) that it's more like combining a white lab and a chocolate lab than a chihuahua and a chocolate lab. Most brewing strains seem pretty similar, and I would imagine they haven't had enough of an opportunity to undergo significant genetic drift from their common ancestor.

To use a botanical analogy, if I were to combine two different heirloom tomato varieties, I would expect to still have something resembling an heirloom tomato, even if it didn't have some of the specific properties of either parent (growth pattern or fruit shape).

theredben said:

Actually, with commercially available yeast (White Labs, Wyeast, et al) they have all been isolated to single cell at some point in the cycle. That is how they have a constitent strain.

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True, at some point. But unlike a poinsettia, you're not watching each individual cell for the properties you're looking for.

bovineblitz said:

True, at some point. But unlike a poinsettia, you're not watching each individual cell for the properties you're looking for.

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Actually they are. A lot more goes on behind the scenes at yeast depositories then we imagine.

winnph said:

To use a botanical analogy, if I were to combine two different heirloom tomato varieties, I would expect to still have something resembling an heirloom tomato, even if it didn't have some of the specific properties of either parent (growth pattern or fruit shape).

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The problem is that Heirloom tomatoes are not propogated asexually, they are let to go to seed. That is a totally different situation.

ni* said:

Genes do not "revert" (nor do traits get "set in the genes"). Modern poinsettias (there are only two "t"s) are, in fact, hybrids, which is exactly why progeny usually have less desirable traits than parental lines.

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Which Euphorbias are they hybridized from, may I ask? And as I worked for a grower who holds multiple copyrights on pointsettias, they are in fact asexually propogated, and the resultant clones are selected until the traits are set. This is why they seem to be analogous to budding yeasts.

Of course they're propagated asexually. That has nothing to do with them being hyrbids.

They are hybrids of Euphorbia pulcherrima, of course. They're not inter-specific hyrbids.

My point about them being propagated asexually was that there are mutations that isolated with asexual propagation, not regular sexual seed trials. This is why I associated them with yeast.

While in the shower I think I understood this a bit better, with yeast you have a pure strain that could hybridize with another strain with predictable (but not neccesarily desirable) results. This would now be a F1 hybrid, which would not be able to sexually reproduce true to it's lineage (which would not matter given that it is a budding yeast). This is assuming you had nothing better do to for the next 6 months or so.:fro:

theredben said:

While in the shower I think I understood this a bit better, with yeast you have a pure strain that could hybridize with another strain with predictable (but not neccesarily desirable) results. This would now be a F1 hybrid, which would not be able to sexually reproduce true to it's lineage (which would not matter given that it is a budding yeast). This is assuming you had nothing better do to for the next 6 months or so.:fro:

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Exactly! I'm not sure I'd say the cross would have entirely predictable results, though. Basically what I wanted to do (until ni* shot down any hope I'd succeed) was a seed trial. I hoped the progeny would have some combination of the traits of the parental lines, but only experimentation would show what combination that would be.

The reason I was inspired to do this was I've got a batch going right now that has a blend of either 4 or 5 different strains in it,* and it made me wonder if I could cross a couple strains, then cross the resulting strain with whatever I bought next for a batch, and cross that one with another commercial strain next time I brewed, ad infinitum, keeping a few slants or jars of each mix along the way so I could backtrack if something went awry. The goal being a unique house yeast.

But I've given up on that goal and I'll stick to collecting wild yeast and trying to find one that produces something drinkable.


* In case you're wondering how I don't know whether it's 4 or 5 strains, it's a healthy pitch of WLP565, a reused slurry of WLP575 (a blend of WLP500, 530, and 550), and I had just used the siphon prior to removing the beer from the WLP575 cake on a batch that had (4th generation) Wyeast 1272 in it. So, a solid slurry of 4 yeasts, assuming all 3 remained in the slurry of the WLP575, plus possible contamination from a 5th strain.

Yeast come in two different mating types. Mix two strains of the same mating type and they will NEVER have sex (barring a mutation to convert mating types). Put two strains of different mating types together and under the right conditions they will have sex. The problem then is each offspring will be different and therefore will behave differently when brewed with. It is quite a chore to sort them out.

Now to the off topic plant clones question. The clones are quite stable. There are apple varieties that have been asexually propagated for over a hundred years with no noticeable changes. However, there are the occasional "sports" where a shoot tip will have a spontaneous mutation. There are in fact numerous apple varieties that were isolated as a sport by a farmer who noticed it in their orchard and decided to propagate it. I believe the seedless navel orange originated as a sport (I think, could be wrong. I don't work on oranges)

You'd really think this would be true, but strangely, it isn't. It turns out that (haploid) yeast cells can switch mating type after ever division, via a fairly bizarre sort of quasi-recombination. This being a huge pain for genetics studies, the endonuclease which triggers this is usually knocked out in lab strains, ensuring fidelity of mating types.

This is, technically, mutation, but since it's targeted, extremely frequent and specified within the yeast genome, it's not really the sort we're used to thinking about.

Sometimes it seems like the more you learn about life, the weirder it seems.