what the plastic is made of. so any molecule that contains C, H (and atoms like O and S F or N depending on the type of plastic) can be synthesized by plastic eating bacteria. so we can also make oil and fuel from it
Metabolism can definitely create useful products. Alcohol is formed from yeast metabolising sugars, for example. Same with miso paste. Hell, we can make milk without cows now via precise fermantation.
Not sure on what the inputs are, but basically bioreactors that have bacteria that are doing the same processes you'd get milk from otherwise. I've done ice cream and protein powder made from companies that used perfect day foods' reactor milk. Actually was a big fan of the vegan whey protein powder, but that company died at some point