I remember this link - about a high school student who's science fair project was a basic but effective selection experiment. He cut up plastic and put it in a yeast medium (growth medium for microorganisms) for a few weeks. It says he tweaked the temperature and other incubation conditions for a few weeks and got a significant degradation of the plastic in the media. The microorganisms in the media were not characterized.
That article is great because the bloggers compiled a list of similar work.
There are a couple of links that point to styrene degradation by Pseudomonas putida variants. Pseudomonas putida is a likely candidate from bacteriology - it was first isolated near chemical and petroleum spills - they can degrade petrochemicals and organotoxics, so researchers might tend to start with this bacteria or an isolate of it.
This paper identifies Phanerochaete chrysosporium, a white rot fungus as an organism that can degrade phenolic resins. White rot fungi are found in wood rot and can degrade lignin which is derived from a poly-phenolic like biosynthesis pathway. So this is also an interesting lead. It doesn't always grow to industrial scale - I've known people working on this even in the early 80s.
So it seems despite the fact that plastic never seems to go away, there are organisms in the wild that will chew away at the plastic, and with a little bit of selection work you can pick them out pretty easily. This survey of the plastic dump in the Pacific gyre found that there were marine microorgs that might be eating plastic there too. They had a preliminary report:
So far, the DNA sequences obtained by her lab show that almost 25% of the bacteria on one polyethylene surface were vibrios
A survey of the tropical rainforest also found a collection of fungi that can subsist on polyurethane. These included Pestalotiopsis microspora which seems to be have the so far unique property of anaerobic degradation of polyurethane.
Overall it seems that finding organisms in the wild is of ongoing interest. This may be because biodegradation of plastic tends to be slow, which makes sense because if it were quick there would be no problem with dumping it into the dirt of into the ocean, but it would also rot over time in the back yard or in your boat. While its possible that more fishing trips may find the perfect plastic eater, its also possible that industrial processes for the bioremediation of plastics may have to wait for some engineered organisms.