From this article in Journal of Clinical Investigation: www.jci.org/112/9/1291
Here are some snippets I thought were REALLY interesting:

“Until recently, bacteria were considered to live rather asocial, reclusive lives. New research shows that, in fact, bacteria have elaborate chemical signaling systems that enable them to communicate within and between species. One signal, termed AI-2, appears to be universal and facilitates interspecies communication.

Not only is AI-2 produced by a wide variety of bacteria, it is also detected by many or possibly all of them.

AI-2 has also proved important in the organization of bacteria into structures called biofilms. Bacterial biofilms can be composed of single or multiple species. In these communities, bacteria live adhered to surfaces and the biofilm inhabitants cooperate in the production of an ECM that leads to the formation of a complex architecture containing structures including “pillars” and “mushrooms.”

The discovery of species-specific as well as universal intercellular signaling molecules reveals that bacteria interact with one another using surprisingly sophisticated mechanisms of communication. In nature, bacteria are rarely found in isolation, and evolution appears to have provided a mechanism that allows them to detect when they are in heterogeneous communities, to assess the proportions of self and other in mixed-species environments, and to respond to this information by appropriately modulating gene expression.”

With communication, collaboration can happen…