Wednesday, August 22, 2012

Quorum sensing

From a short description of the work of Bonnie Bassler:
"Silverman ended his talk saying “‘Don’t you see, these bacteria are communicating with this molecule. They are acting multicellular.’” At the end of his talk, Bassler steamed to the podium and ask Silverman for a job. Much to her surprise, he offered her a postdoc position right there. She packed her stuff and returned to California and began studying bioluminescence in the marine bacterium V. harveyi.
During her postdoc, Bassler defined the QS circuit of V. harveyi. She showed that, like V. fischeri, V. harveyi communicated with other members of its species by using a chemical signal called an HSL autoinducer (3). The marine bacteria secrete this autoinducer into their environment. As long as bacteria are in low numbers in dilute suspension the autoinducer is washed away and no act is being taken, but when bacteria replicate and grow in number, the concentration of the autoinducer molecule also increases in the surrounding. When it reaches a certain threshold it is sensed by the bacteria and gives it an indication of its own population size. They then respond simultaneously by activating their light genes to produce bioluminescence. As Bassler puts it so nicely in her TED talk, “they vote with these chemical votes, the votes get counted and then everybody responds to the vote”.
Bassler also discovered that V. harveyi had more than one molecule for QS; she called this additional molecule autoinducer-2 (AI-2) (3, 4), and the original, found by Hastings, became autoinducer-1 (AI-1).
So… you can legitimately ask what’s all the fuss about understanding the genetic and chemical basis of how marine bacteria talk to each other and produce light?
It turns out that bacteria use QS not only for bioluminescence but also for many other important traits, most important of which, virulence (5-8). Actually, in this regard bacteria act very similar to us; if you would want to do something that’s beyond your reach as an individual, you’d talk to some other guys, get the necessary quorum, and then carry it together. Bacteria use exactly the same strategy, or as Bonnie puts it, “they are just too small to have an impact on the environment if they simply act as individuals”.
Thinking of it, bacteria are microscopic creatures, and probably their only chance to overcome a huge host is by acting together. So they count them self up and only when the right amount of cells is present they launch their virulence attack to take over their host.
And this simple realization, has huge implications for human health. "
Her Ted talk, which according to Carl Zimmer is one of the good Ted talks and a description of the talk towards the end of the blog post Microbial Hermeneutics - 2 which also links to a later interview.

1 comment:

johnpeterjohn said...

your description seems good..

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