Bonnie Bassler, a molecular biologist at Princeton University discovered that Bacteria can communicate, across species borders, using signal molecules. Synchronisation between individuals in a biofilm, Quorum Sensing, can launch attacks that overwhelm an immune system.
It’s an important mechanism to bacteria, so it even has a genetic backup, multiple redunant communication channels. And at least one of them works across species barriers. She says in Discover:
What they first do is they scan the environment. And they’re asking the simplest question: “Am I alone or am I in a group?” They just look for any quorum-sensing molecule. Then, the more sophisticated question that I think they ask is, “Who is that?”
They can say, “You are my absolute identical twin.” They can say, “You’re my extended family.” And then they say, “You’re some other species.” They’re not just counting. There’s information encoded in these molecules that tells a bacterium who that neighbor is — how related they are. And depending on the ratio of those three molecules, they understand whether their family is winning or losing.
Sabotaging Quorum Sensing in biofilms can help fighting dangerous infections by disabling the communication and sensing methods of the bacteria.