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Thread: Custom made yeast

  1. Default Custom made yeast

    Hey all,
    So and introduction to start. I'm a senior biology student with a focus in microbiology. The other day I came up with an...interesting research project. What I'm planning is to take some specific genes from a lactobacillus strain (the bacteria that they use to make sour beers) and put them into a brewing yeast. All of the details aren't set just yet, but the idea is to make a yeast that behaves normally under normal brewing conditions, BUT when you add lactose, it produces acid, making a sour. So basically you'd have a normal brewing yeast that you can also use to make sours, just add lactose, and you don't have to worry about contaminating your brewing gear with bugs that are hard to get rid of, it'd just be yeast that works just fine as long as you're not using lactose.

  2. #2


    Are you using lactose as the acid precursor OR are you using lactose to turn on your acid synthesis genes?

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  3. Default

    As the acid precursor. I was planning (this is still in the very early stages) on using the genes for Beta-galactosidase and Beta-galactoside permease out of the bacteria and putting it into the yeast, so that it can always ferment lactose into acid (hopefully). That way I'm limiting the number of genes I'm working with while still getting the desired effect.
    Of course, there's always the possibility that it'll end up just turning the lactose into alcohol instead of acid, so this project will probably be a bit more complicated than I'm hoping.
    Did that answer your question?

  4. #4


    The initial issue that I see is that genetically altered bacteria will ONLY ferment lactose when all glucose is removed from the media. This means you would have to brew completely dry, then add the lactose to see any results. Since this gene is used in a lot of research tests, you may be able to order yeast that are already altered with this gene.

  5. Default

    Yeah, the gene set that does that is called the lac operon, which is an inducible operon (that means it needs certain conditions to turn it on before the proteins get made and it works). I'm gonna try to pull a couple of the genes OUT of the lac operon so that I'm only getting the bits I want and so that it's always on. We'll see how it goes.

  6. #6


    It'll be interesting to see if you get that to work. I would worry that by doing that you will create a strain that is weaker than normal because of the increased energy requirements and the decreased energy output. This could lead to the yeast being less aggressive and cause it to be out competed by bacteria or other contaminants. I'd recommend very strong sterility measures when using it. Since the glucose/cAMP segment of the lac operon occurs at the initiation site, I am not sure that you will be able to remove it and have a functional gene segment. You will need to replace the initiation site with one that is always "on".

  7. Default

    True. I'll post on this thread as things develop. It'll likely be slow going, if it happens at all, but I'm pretty excited about it.

  8. #8


    Another, easier option may be to point mutate the initiation site so it no longer binds to cAMP but still binds the polymerase and lactose. When I get home from the lab I will do a little research and see if I can find any on this topic. I haven't worked with the lac operon in over a year, so I'd have to review it a little to remember the details. Thankfully the bacteria I deal with usually come with it already encoded and I dont have to mess with it myself!

  9. Default

    I'm still an undergrad, so pretty much ALL of this is new to me.
    The more I think about it though, the more I worry that just putting in the lac operon won't be enough. What I'm thinking is that B-galactosidase will break the lactose into glucose and galactose, which will then go down the yeast's normal fermentation pathways into alcohol. What I'm afraid I'd have to do to make this work, is find a way to shut down the normal fermentation pathways in the presence of lactose AND start up a new pathway that produces acid. All in all, I doubt that this project will end up being feasible.
    Thanks for helping me think it through though!

  10. #10


    I haven't done any work with yeast myself genetically. And it seems that those who do don't publish their work. I could find very little info on yeast operons that are available. Since yeast has a dsDNA instead of ssDNA, it may cause you some difficulties in getting the DNA to splice into the cell. I would love to see a yeast version of zymomonas mobilis to help increase the alcohol concentration that can naturally be obtained in fermentation of the mead.

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