Bioengineers at MIT have modified e. coli bacteria in two ways: rather than smell like human fecal matter, their E. coli cultures smell like mint when they’re growing, and banana when they are mature.

If they can do that, can should be able to devise metabolic pathways that breaks down plastics into carbon dioxide, which then can be metabolized, which will render plastic biodegradable.  However, to mitigate the global warming effects of the carbon dioxide, they also need to figure out ways to sequester the carbon.