How Do Single-Celled Organisms Act in Groups?

Today, I'm going to write about one of my all-time favorite TED Talks:
How bacteria "talk" by Bonnie Bassler

The talk is on a concept known as "quorum sensing". I think I first learned of the concept of quorum sensing back around 2004, in Science News Daily. I was already intrigued at that point, but in this TED video, Bassler really brings it to life.

In this fascinating video from 2009, Bassler introduces the topic with a quick overview of bacteria. She begins by demonstrating the importance of bacteria, noting that the human body contains 1 trillion human cells and 10 trillion bacteria cells, and goes on to note that humans have 30,000 genes in our bodies with 100 times as many bacterial genes, so by her reckoning, humans are 90 or 99% bacteria. (Note: I happened to read today in the PLOS article, Revised Estimates for the Number of Human and Bacteria Cells in the Body, from August 2016, that an updated estimate is 3.8 trillion bacteria and 3 trillion human cells, which is what reminded me of this video.)

She goes on to note that bacteria do useful things like protect our cells from external insults, digest our food, make vitamins, and help to keep bad microbes out of our bodies. She also mentions some harms that specific bacteria cause, such as lyme disease, toxic shock, food poisoning, ulcers, and cholera.

This array of capabilities led the people at her lab to wonder how it is that bacteria do anything? They are so small in comparison to human cells, that - as individuals - their effects should be negligible, so how do single-cell organisms act to accomplish things in groups?

She introduces the concept of quorum sensing by describing a particular symbiotic relationship between a squid and a species of luminescent bacteria. At night time, the bacteria emits light, and the squid adjusts a shutter in its body so that the light emitted by the bacteria beneath the squid exactly matches the light overhead, which prevents the squid from casting a shadow. In day time, the squid pumps out 95% of the bacteria colony, the light goes off, and the squid sleeps. During the day, the bacteria reproduce, so they're ready to produce light again at night time. The question is, how do the bacteria know to go dark during the day time?

The answer to that question is that the bacteria emit a signaling molecule which is sensed by others. If there are few bacteria nearby, the molecule drifts away, but if many are in close proximity, they know that they're in the presence of a group, and they light up. After researchers discovered this behavior, they discovered that all bacteria have similar systems that govern hundreds of different types of behaviors.

One of the important behaviors that is governed this way is virulence. If an isolated bacteria got into our system and became virulent, our immune systems would immediately overwhelm it. So what they do, instead, is to lurk in our systems doing nothing but emitting their signaling compound. Only when they detect enough other bacteria of the same type do they turn virulent, at which time our immune systems can be overwhelmed.

Another interesting finding is that each species of bacteria has its own unique and private signaling molecule for intraspecies communication, and they also have a common molecule for interspecies communication. So bacteria are able to keep approximate counts of how many of their own species and other species are nearby.

As you may be aware, a looming problem in the pharmaceutical industry is antibacterial resistance, seen here under time lapse video:

Bassler notes that quorum sensing can be harnessed to reduce the pace of antimicrobial resistance by preventing the bacteria from sensing or receiving the signaling molecules. This would prevent disease without creating selective pressure by killing them.

She closes the talk with four takeaways:

• Bacteria talk to each other using chemicals.
• Bacteria are multi-cellular, meaning that they carry out group tasks that individuals could not accomplish.
• Bacteria can distinguish self from other.
• Pharma-strategies can be developed to impede/improve quorum sensing.

Conclusion

While the idea of quorum sensing among bacteria is fascinating enough, what I really think is exciting about it is that it can also be used by humans in social media or smart phone applications. Isn't steemit's up-vote almost a form of quorum sensing among humans? How could that quorum sensing be used to go beyond awarding payouts to actually coordinating group behavior (like steemfest)? The possibilities, I think, are limitless.

One difference between bacterial quorum sensing and the steemit up-vote is that molecular signaling coordinates behavior in time and space, because the molecule drifts away. It would be as if the voting percentage gradually diminished over time, and needed to be replenished in order to signal continued support for a post or action. Possibly an idea for some future web site or application to pursue.

I hope you enjoyed my write-up, but I highly recommend watching the video. Here's a link again, to save you some scrolling.

About the Author: @remlaps is an Information Technology professional with three decades of business experience working with telecommunications and computing technologies. He has a bachelor's degree in mathematics, a master's degree in computer science, and is currently completing a doctoral degree in information technology.