I bet this will lead to huge imbalance in the world of micro-organisms, the effects of which, we do not understand.
For comparison there's at least 1,000 times as much biomass grown per year as there is plastic produced per year.
My numbers are off however, my figure for biomass production is only the weight of the carbon. I can't seem to find numbers for total production.
Especially since the majority of the weight of a plant is in the water - which has no carbon.
Although there may be an issue with diversity and horizontal gene transfer - I am uncertain what impact that will actually have - especially given how fast bacteria adapt in the first place in proper conditions.
Also no chance that it will evolve sideways to decide it likes to eat other things?
I hope they keep it contained. After other notorious attempts to do things like this (aka cane-toads in Queensland Australia etc) I dont like to think of what happens with something nearly invisible as bacteria and as wide spread as plastic...
If the bacteria only eats plastics then it has an uncontested food supply that nothing else will touch. Other bacteria are unlikely to suffer.
Warmth isn't actively being competed over since it can be obtained fairly easily by non-cooperative means instead.
Predators already exist. Virophages that can kill this bacteria are likely to evolve quickly considering they cover every surface on this planet. If it gets out of control, simply introduce the correct phage. They happily terminate 40% of all marine life every day so I think some plastic bacteria won't be trouble.