Awesome project but I don't think this really counts as solving the problem of plastic bags:

* Ideal conditions are unlikely to be encountered in the wild.

* Plastic bags are spread out throughout the environment. How to get the plastic-munching bacteria to this disparate plastic isn't solved. (If all the plastic is in one place, well, we've got recycling already).

* The existing bacteria in the world will probably outcompete the bacteria this guy has developed.