Scientists at UCSB found a type of Amoeba in the ocean that eats plastic wrap! When the Amoebae grew on the plastic wrap, they made holes in it. So that is one way to biodegrade plastic.

Another way to biodegrade plastic is to make new types of plastic that lots of kinds of bacteria and micro-organisms will eat. One kind of biodegradable plastic is made from corn. I have a coffee mug from corn plastic, and 'green' festivals often have disposable plastic silverware made from corn plastic. My corn plastic coffee mug says not to wash it in the dishwasher, and one of my friends' mugs melted when she washed it in the dishwasher. I don't like corn plastic, because corn is a food, and we need to use our corn to feed people.

I searched plastic 'biodegradable plastic' on google.com, and there were lots of hits. One hit says:
Environmentally Safe Acetate Film Made From Wood & Cotton: Learn More