Ethan Zuckerman’s online home, since 2003

Bonnie Bassler and bacterial communication

This post is part of a series from the TED 2009 conference held in Long Beach, California from February 4-8th. You can read other posts in the series here, and the TED site will release video from the talk in the coming weeks or months. Because I’m putting these posts together very quickly, I will get things wrong, will misspell names and bungle details. Please feel free to use the comments thread on this post to offer corrections. You may also want to follow the conference via Twitter or through other blogs tagged as on Technorati.

Bonnie Bassler doesn’t really think of you as human. She thinks you’re mostly a big bunch of bacteria. She points out that the average human as a trillion cells, but hosts outside and in ten times as many cells. This means that humans have 30,000 genes, but you’re carrying maybe 100 times as many genes in your bacteria.

We think of bacteria as bad, because there are so many dangerous bacterial diseases. But most bacteria are beneficial and aren’t free riders – they act as body armor against external insults, digest our food, make vitamins and educate our immune system.

But here’s what’s really cool – bacteria talk to each other. They can conspire and cooperate.

She’s studied a bioluminescent bacteria called Vibrio Fischeri. In loose concentrations, the bacteria doesn’t glow – tightly packed, it does. The reason is that the bacteria emits a chemical signal – if the cell density is high enough, the molecules can sense each other and know to glow in synchrony.

These bacteria live in symbiosis with a particular squid which uses them to hunt. The bioluminescence counter-illuminates the squid so it leaves no shadow on the ocean floor, hiding it from predators – “it’s the stealth bomber of the ocean”. Every night, the squid pumps out the bacteria, leaving only a few behind. At low concentrations, they don’t glow – when they reproduce, they glow again the next night.

It’s worth understanding the mechanism that these bacteria use for collective behavior as a form of language. Bassler calls this phenomenon “bacterial quorum sensing”. It’s a form of chemical voting, and it appears to be used by a huge set of bacteria. One key place it’s used is in producing pathogens – a bacteria acting alone cannot possibly poison you… but using quorum sensing, they can coordinate and release pathogens at the same time, making you ill.

As she’s studied bacteria, she’s seen similar structures around this chemical signalling – the left side of the molecules is identical and the right side is different. Each bacteria speaks a slightly different, but related language. One language is specific to a species; another is “an interspecies trade language”, a language of communication that can coordinate between different species of bacteria.

Using these languages, bacteria are able to count how many there are in one species and how many in other species. That allows bacteria to make “decisions” about which bacteria should act and which shouldn’t.

The chemical signaling is based on a very simple, five-carbon molecule. “It’s a bacterial esperanto,” she tells us. This might mean we could design antibiotics based on jamming this molecule. Her team has developed molecules that can jam quorum sensing for specific species, or for all species, a powerful broad-spectrum antibiotic which doesn’t kill cells, just shuts them up.

Most intriguingly, she believes that communication between bacteria may have been the evolutionary pathway towards multicellularity. “Bacteria laid down the rules that multicellular organisms live by.”

My favorite talk so far, hands down – amazing (and slightly scary) stuff.

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