I am writing a book in which criminals get their hands on a polymer which resembles chewing gum , but alters their saliva. This allows them to burn holes into walls made from plastic used as building material in an alternate future of earth.

-Is it possible to create a "gum" that alters saliva enough to burn through plastic without significantly harming the user?

  • the word plastic is being used as a generic placeholder for any plastic that will allow for this situation to take place
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    $\begingroup$ I'm not aware of anything that would do that in the speed required, but there are many proteins (well, mostly a number of proteins working together) that are quite good at breaking down all sorts of polymers. The problem would be that they need a starting point (where the polymer chain ends), but that could be accomplished by simply scratching the plastic in the area to be "melted". If you are ok with not naming a specific chemical but just saying Portein mix X, you can work with that. Most writers would go with something like nanites/microorganisms though $\endgroup$
    – Raditz_35
    Jul 31 '17 at 14:44

Scientists Just Discovered Plastic-Eating Bacteria That Can Break Down PET

Enzyme innovation

Now a team at Kyoto University has, by rummaging around in piles of waste, found a plastic munching microbe. After five years of searching through 250 samples, they isolated a bacteria that could live on poly(ethylene terephthalate) (PET), a common plastic used in bottles and clothing. They named the new species of bacteria Ideonella sakaiensis.

You may think this is the rerun of an old story, as plastic-eating microbes have already been touted as saviours of the planet. But there are several important differences here.

First, previous reports were of tricky-to-cultivate fungi, where in this case the microbe is easily grown. The researchers more or less left the PET in a warm jar with the bacterial culture and some other nutrients, and a few weeks later all the plastic was gone.

PETase explained

Bottle breakdown. Illustration: P. Huey. Reprinted with permission from U.T. Bornscheuer, Science 351:1154 (2016)

Second - and the real innovation - is that the team has identified the enzymes that Ideonella sakaiensis uses to breakdown the PET. All living things contain enzymes that they use to speed up necessary chemical reactions. Some enzymes help digest our food, dismantling it into useful building blocks. Without the necessary enzymes the body can’t access certain sources of food.

The enzyme that the bacteria uses has been named PETase. Just as the Amylase in our saliva breaks down carbohydrates, PETase breaks down PET. It would be very similar to a hard-boiled sweet melting in your mouth, except... ya know, spitting on a wall.

I'm not sure how you would get the salivary glands to produce PETase aswell as Amylase though. Maybe through a process similar to the one used to genetically modify bacteria to produce Insulin?

If this hypothetical chewing gum had the ability to genetically modify some (not all! You still want SOME amylase for eating purposes!) of the cells in the salivary glands, then it could be possible to have them produce PETase.

NOTE: On the subject of sweets melting in the mouth, it would take just as long to melt through your walls. Unless you want to stand licking a wall for hours (and accidentally ingesting small amounts plastic), it will not be a feasible choice. However, thanks to imagination and suspension of disbelief, anything can happen in a book! Maybe this is "Super Awesome PETase which melts through plastic in seconds!" and you spread it in the outline of a door and bust through?

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    $\begingroup$ +1 especially given that enzymes can process a lot more substrate than their own weight. $\endgroup$
    – Mołot
    Jul 31 '17 at 15:08
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    $\begingroup$ +1 a good attempt in solving OP's issue and perhaps a possible solution for reducing the amount of plastic floating on the ocean? Well done. $\endgroup$
    – CPHPython
    Jul 31 '17 at 17:03
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    $\begingroup$ The burglars could chew some gum containing PETE-eating bacteria (to activate the bacteria), gargle some water (to dilute the bacteria into a larger volume of liquid), smear the diluted PETE-eating bacteria on the wall in the shape of a door or window, come back in a few hours to the weakened wall, crack open the door, and enter the building. $\endgroup$
    – Jasper
    Jul 31 '17 at 18:20

Even if the gum replaced your saliva with a strong acid (that miraculously you aren't affected by) you don't have enough saliva to be able to melt through a wall.

The average human produces about half a liter of saliva a day. If you spent your entire day licking the wall that is the maximum amount of acid you would be able to apply to a wall.


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