system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 The Bacteria that eat plastic; Is this scalable to tackle plastic pollution? Will they multiply uncontrollably? What is the by-product they produce?
gpt
Is it scalable to tackle plastic polution? Yes and no. The bacteria that eat plastic are probably not going to be released into the environment just because it would be inefficient from an industrial perspective. It would be way more effective to round up boatloads of plastic waste from the environment and put in in a vat full of this bacteria to digest it. The other aspect to tackling global plastic polution is that these bacteria can only degrade one type of plastic and if you walk around your house you'll probably find at least 7 different types of plastic with different numbers in the little recycle symbol on the bottom. So the global plastic polution problem is much more complicated, but this could be a really useful remedy for one especially common type of plastic. 

Will they multiply uncontrollably? No haha, no they will not. This was the concept behind an interesting scifi comic book from the 80s or something where an organism developed the ability to eat plastic and then started devouring cars and cities. Its a fun though, but this would not happen. Especially if this bacteria is used in an industrial setting, these kinds of batch digestions are really common. It would be a lot like brewing a beer where you set everything up in a thousand gallon fermenter and then you let it sit for a month or two to fully degrade. In that fermenter, you might have to be careful about what kinds of plastic you use because the bacterium can degrade certain types of plastic. The other thing about fast/uncontrollable growth to keep in mind is that the degradation of the plastic is abyssmally slow. That initial step where a single molecule is pried from the polymer is way too slow to support any kind of rapid growth. 

What is the byproduct they produce? This is a really fun question because there are a lot of answers to this. To answer with another question: what are all the things you can do with carbon? Bacteria are incredibly effective at taking in waste products and spitting out valuable stuff like insulin, antibiotics, or industrially useful chemicals. One way that this plastic degradation could be used is to recover the original plastic monomers. This would generate a supply of plastic ingredients that doesn't depend on any additional fossil fuel input. If you want to learn a little more, the search term "circular PET economy" will help.