Bacterial evolution & glycine withdrawal experiment

13:26DNA. Okay. So without >> Mhm. >> this pathway, it can no longer grow because it can't make DNA and it can't make proteins. This is we're creating almost this like artificial famine at this at the cell level. >> Exactly. >> Um and requiring it to go through this pathway that will generate an output we care about in order to be able to literally feed itself. >> Feed itself. >> Yeah. Yeah. And then and then comes the production line. So now how does it actually make the food that it needs? Right. >> What we do >> is we put a bunch of genes on a plasmid. A plasmid is a circular bit of DNA that we can use to change what the bacteria is producing. It's just foreign DNA that we can like plug in. Now, these bacteria are already

14:07stressed out because they can't eat. So, they're just trying to take in whatever whatever help they can. They we put in this plasmid that has genes on the plasmid to create >> this artificial pathway. Okay? Where on its way to creating zanthamatin, what it's going to do is create formate, which is a precursor for tryptophan and all of the all of the other things that the bacteria needs. >> Right. Right. Right. Right. >> And the ultimate goal is you've got like a sole carbon source which is through the factory. >> Yeah. You have to go you have to you have to pay the cost to be the boss. You literally you have to go kiss the ring >> to survive. >> To survive. Yeah. And [laughter] and

14:49even then it wasn't so simple. Okay. because you have that single carbon source, but the bacteria still the initial bug was it still needed supplemental glycine and lryptophan, which is >> two kind of expensive ingredients that you need to give the bacteria in order to survive. You can't just give it glucose. So then what they did was they had another evolutionary lab in their little lab. Okay, what you do is you say, "Okay, I need you to make glycine, right? I'm going to give you a bunch of glycine at first and I'm going to slowly wean off your entire population of glycine and you're hoping that the bacteria just learn through some mutations because of this pressure

15:31they're going to learn how to make their own glycine. >> Yeah. >> Either learn how to make their own glycine or live without it. >> Yep. >> Okay. And that's exactly what ended up happening. Y >> they they they the bacteria had a single amino acid change in the met gene and then all of a sudden they didn't need glycine. supplemental glycine. >> You're you you you were sort of basically through this uh providing withdrawal mechanism >> uh driving [snorts] evolutionary progress to basically fulfill the gap of the withdrawal of providing it directly to >> interesting and it worked. >> And it worked, right? [laughter] What's And what's cool about this is like >> this entire pathway, right? You've got

16:12the factory that's going in. Yes. it the factory that they're using that that they've put in through this plasma through this foreign DNA the stuff that they got from the octopus and whatever um that can't just be the native factory because it has to have a byproduct that encourages the bacteria to actually work right so it has to be leaky in some sense >> I understand what you're saying not all of the carbon can go into the zanthamatin >> production some of it has to go out yeah some of it has to go out in order to create formate and then become this like sole carbon source. >> Yep. Yep. That makes sense. So the the factory has sort of two functions. Both creating what we care about um and also providing enough for the the cell to

16:53continue to propagate. >> Yeah. Yeah. Yeah. And then those that ran the factory more actually had an advantage because they're the ones that could actually grow. >> Yep. >> Yeah. It's pretty crazy. >> That's really crazy. >> It's really crazy. And one of the ways that they actually showed that this was happening is an old school technique where you take um you take an isotope of an atom. In this case, instead of carbon 12, they used carbon 13. >> Okay? >> And they and they fed it glucose with carbon 13 in a specific part of the glucose molecule, second from left or whatever. Um,