Bacteria Know When to Turn Deadly

Bacteria may not seem like social, communicating creatures, but they "know" when to turn deadly thanks to a unique signaling system called "quorum sensing," according to a new study.

These single-celled organisms can sense when their population reaches numbers in the millions, and only then will they turn deadly, knowing that there is strength in numbers.

The quorum-sensing messages, which switch bacteria from innocuous to pathogenic, from unhelpful to helpful, are carried in small molecules that the bacteria release and whose concentration bacteria can measure.

Blocking such a signal can prevent a bacterium from essentially "turning nasty."

To study this phenomenon, researchers from the University of Wisconsin-Madison have made artificial compounds that mimic the natural quorum-sensing signals, including some that block a natural signal from binding to its protein target.

In the study, published in the journal Chemistry & Biology, they changed key building blocks in these protein targets one by one.

"If that part of the protein is important, the change will have a significant effect on our signal's activity," study leader Helen Blackwell explained in a statement.

"It was surprising that making minor tweaks, very subtle changes, to the protein would convert a compound from an inhibitor to an activator, or turn an activator into an inhibitor," she added. "That shows that small-molecule control of quorum sensing is very finely tuned, much more than we even expected."

Quorum sensing is present in the majority of, but not all, bacteria. It's advantageous in that a few hundred bacteria cannot overwhelm an animal host, so by lying low until they number in the millions, they can easily take over the immune system without risk of being harmed in the process.

By learning more about this on/off switch, the research can possibly lead to more effective antibiotics that can tap into this quorum sensing rather than trying to outright kill the microbes.