Bacteria, Pancakes, and David X. Cohen


Is your E. Coli bored and listless? Has it become lazy as it idles away the hours inside your gut? Then take heart: scientist have found a way to turn this bacteria into a working machine! Here’s what they did:

First, they made a computer from a circular piece of DNA called a plasmid. (Which to my eyes is sort of like saying, “First they built a time machine,” but what do I know? Not enough to build either DNA computers or time machines, that’s for sure.)

Then they took this little DNA computer and stuck it in a piece of E. Coli. It looked something like this:

Then they gave the E. Coli a math problem to solve, because everyone knows that bacteria love to do math. And the math problem that they chose is called the Burnt Pancake Problem, which goes something like this:

Suppose that you made a bunch of pancakes, and because you’re not the world’s greatest cook they all came out to be different sizes. Further suppose that you got distracted while cooking and the pancakes came out burnt, but you piled them up anyway, in some random order. But then you decided that, having already amassed two strikes what with the different sizes and the burn marks, you didn’t want to add to the problem by having the pile be so disorderly. So you put your spatula under some of the pancakes and flip that pile over, then put your spatula under some more and do another flip, etc. How many flips would it take to end up with a stack ordered with the largest pancake on the bottom, then the next largest, all the way to the smallest pancake on top and have the burnt parts hidden at the bottom, where hopefully they’ll be too covered in maple syrup to be noticed.

This was a good problem to give to bacteria because it’s reasonable to assume that E. Coli would like to think about food (although they might not appreciate the burnt part). And it’s a good problem because it was talked about in a math paper by David X Cohen, of The Simpsons and Futurama and Beavis and Butthead fame, which are shows that E. Coli enjoy watching. [The paper is “On the problem of sorting burnt pancakes” by D.S. Cohen and M. Blum, published in 1995 in Discrete Applied Mathematics (61, 105-120).]

The scientists simulated this pancake problem by injecting different sized segments of DNA into the E. Coli. Only two, because this is kind of a new thing and apparently two pancakes/DNA strands is plenty hard for a microorganism. At any rate, the E. Coli worked really hard and flipped it around, using an enzyme borrowed from its good friend Salmonella (because who said that E. Coli was the only hard-working bacteria around?)

If all the pancakes/DNA got switched around into the correct order, the bacteria became resistant to the antibiotic tetracycline as a reward. This was important because when the scientists decided that the E. Coli has had enough fun flipping hotcakes, they added some tetracycline and wham any slacker E. Coli were killed. No partial credit here. Then the scientists threw a party for the rest, published a paper, contributed to an article in Scientific American, and called it a night.

For a way cool cartoony technical explanation of this whole situation, check out the animation E.HOP. You know you’ll love it based on the title alone.

The E. Coli computer was created from this image of E. Coli (public domain because it’s from the government) and this image of a computer (GNU General Public License).

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3 Responses to “Bacteria, Pancakes, and David X. Cohen”

  1. ladyhamlet Says:

    Off-topic, but wonder if you guys have seen this:

    I have seen the polygon posts in this website and wondered if you’ve done any polyhedra post.

  2. Ξ Says:

    That’s really cool — thanks! I know I’ve thought about polyhedra, but offhand the only polyhedral posts I remember were the one about Kepler’s model of the universe and a post TwoPi did on polyhedral calendars.

  3. 4, 6, 8, 10, 12, 14,….What comes next? « 360 Says:

    […] to find the smallest number of flips for each configuration is tough. Fortunately, as described in this earlier post, we have E. Coli to help us figure it out. [They give the E. Coli a configuration, let them do a […]

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