Are there organisms that have incorporated (manmade) plastic into their lives in any way? Either in their diet, or as a part of their body?
Biodegradable waste is a type of waste which can be broken down, in a reasonable amount of time, into its base compounds by micro-organisms and other living things, regardless of what those compounds may be.
- from wikipedia
So yes, there are microbes which are capable of biodegradating manmade plastic. It depends on plastic types.
If you meant creating new pathways to biodegradate non-biodegradable plastics, then I don't think so. My opinion that by some of those plastics there are theoretical barriers (e.g. energy barriers or toxic byproducts), and by some of them evolution might create a pathway in time (I don't think in our lifetime, but nothing is impossible).
There are microbes which build plastics to store energy. They are just polymers like starch or cellulose (sugar polymers), with different building stones... Afaik the first biodegradable plastics came from here, but so they were very expensive. Nowadays we don't need microbes in the polymerization process, e.g. we can create polylactic-acid without the presence of microbes.
I have found an interesting article in the topic.
Now, for the first time, researchers have found detailed evidence that bacteria in an animal’s gut can safely biodegrade plastic and potentially help reduce the environmental impact of plastic in landfill and elsewhere. The animal in question? The humble mealworm – which turns out to be not so humble after all.
Researchers led by Stanford University in US and Beihang University in China found that the mealworm – the larval form of the darkling beetle – can safely subsist on a diet of Styrofoam and other kinds of polystyrene, with bacteria in the worm’s gut biodegrading the plastic as part of its digestive process. The findings are significant because it was previously thought that these substances were non-biodegradable – meaning they ended up in landfill (or worse, our oceans, where they’d accumulate for decades).
I don't know if this qualifies as "incorporated ... into their lives", but Hermit crabs use all sorts of man-made materials as housing/protection. If you do a google image search on "hermit crab plastic you will see many examples, including plastic waste.
There are also other animals that use random materials that are lying around to construct housing/cases, and I can imagine that e.g. Trichoptera larvae will occationally include pieces of plastic in their cases. At least they will use gold and pearls (when not given an option). However, these are not really examples of species that have adapted specifically to plastic to use it as a resource.
One example: The Satin Bowerbird (Ptilonorhynchus violaceus).
The males of this species build structures out of sticks (suprisingly called bowers) that they decorate with blue items to attract potential mates. Recent research has shown that the males have began incorporating plastics into these structures for courtship.
A google image search can confirm pictures of this. In this study: "Sexual selection drives rapid divergence in Bowerbird display traits" researchers provided the birds with square plastic tiles, that were ultimately incorporated into bowers.