But don't snickerONR-sponsored Bonnie Bassler won a MacArthur Foundation 'genius award' last year for her research on how some of the most deadly microbes we know cholera, plague, TB, just to mention a few communicate surprisingly well.

In her Princeton Lab, Bassler (and the rest of the microbiology community) calls it 'quorum sensing.' When microbes sense that there's more than just a few of them around (i.e., increases in cell population density), a sort of gabfest starts, and this can lead to the production of toxins that make us very, very sick.

Microscopic organisms must rely on simple, yet complex (depending on how you look at it) means of communication. "Quorum sensing" was first discovered in two bacteria in the belly of the cuttlefish: Vibrio harveyi and Vibrio fischeri. These fellows emit light in response to increases in cell population density they release and detect hormone-like molecules called autoinducers that accumulate in the surrounding aquatic environment as the bacterial cell density increases.

Working with Vibrio harveyi and Vibrio fischeri Bassler and her colleagues discovered that bacteria express a gene called LuxI, which results in the release of special chemicals she calls autoinducers (AI-1) which, in turn, bind to proteins called LuxR on other bacteria nearby. Once the LuxR is activated, a multitude of cellular effects, varying by species, is performed. This is especially useful to bacteria in sensing the size of their colony. Each bacterium constantly emits AI-1, as the number of individuals in a colony grows, so does the amount of AI-1 surrounding them. Once the colony reaches a certain size, a quorum, the amount of LuxI is sufficient to trigger cellular effects. Scores of bacteria species use this quorum sensing every day.

But why would bacteria care how many others are around them? Bacteria are the biggest biomas
'"/>

Contact: Ed Walsh
walshe@onr.navy.mil
703-588-1010
Office of Naval Research
29-Apr-2003