Quorum call, without voices

Is there anybody out there?
When it comes to political intrigue, it’s important to know whether you stand united or alone. Are you surrounded by friends or enemies? Is it time to lead the charge or wait for reinforcements? Tallying how many supporters you have—or how many enemies are waiting in your midst—can be critical to your success.

For bacteria, things aren’t much different. Bacteria survey their surroundings for others of their kind, and others NOT of their kind. They may wait until they have sufficient numbers to launch an attack on your body, or to coordinate effective mining of a nutrient source. But bacteria don’t have eyes, ears, or a mouth; they cannot see, hear, or speak. So how do they tell who is out there?

The peril of the tennis ball
Time to use your imagination, folks. Imagine you are in a windowless room. The door is closed. You are wearing a blindfold and earplugs. You cannot speak. In your hand is a fuzzy tennis ball. When you throw the tennis ball, it bounces off the walls until, eventually, it stops. Think about the chances of the ball ricocheting off a wall and hitting you in the head.

Now remember: you cannot speak, you cannot hear, you cannot see. But, if I put another person in the room with a tennis ball to throw, do you think you’d be able to tell you were not alone in the room? Maybe. How about if I dropped in TEN people, each with one tennis ball? How often do you think you’d be smacked square in head?

It probably seems strange to imagine all this blindfolded tennis ball throwing, and I’m pretty sure it won’t give you a better understanding of human politics. But if you understand how you’d be able to sense the presence of more people in the room based on how often you got a tennis ball concussion, you understand the microbial behavior called quorum sensing.

Bacteria don’t throw tennis balls, they “throw” chemical signals
The tennis ball in our thought-experiment represents a quorum-sensing signal. These are chemical compounds that bacteria can “throw” out into the environment, and “catch” if they hit the cell. In this way, bacteria can sense if they are relatively alone, or if they are surrounded by thousands of others.

If you play around with the tennis ball room scenario, you can start to envision more complex issues with quorum sensing. Can you imagine ways to trick the bacteria into thinking they were not alone? Or trick a crowd of bacteria into thinking they were all alone?

Microbial Grappling Hooks

It's a common theme for my view of microbes: for many real-world problems, microbes have already developed a solution.

Want to turn biomass into fuel? Microbes can do it!
Want to seed clouds for rain? Microbes can do it!
Want to move around using a grappling hook? Microbes can do it!

I've had the honor of contributing a blog entry to the delightful blog "Small Things Considered" on the topic of microbial grappling hooks, known more technically as "Type IV pili." It's basically a rope or filament that is sticky at the end. The bacteria can extend this filament out of the cell, and if the sticky end catches on something the microbe can pull itself along by reeling the filament back in. This is just one of many fascinating structures bacteria can use to interact with the world around them.

If you want a little more technical detail on how Type IV pili work, check out my "Small Things Considered" blog entry on the subject!