The molecule is a key signal in an activity called quorum sensing -- the ability of certain bacteria to perform functions only when they are part of a sufficiently dense population.
The discovery, published in the Jan. 31 issue of Nature, culminates years of searching for the signaling factor and also is of interest to scientists because the molecule turned out to contain the element boron, which has almost no other known use in biology.
"It is a detective story -- one with a surprise ending," said Princeton University biologist Fred Hughson, who led a team of researchers through a series of painstaking and unorthodox approaches to identify the molecule one atom at a time.
The search began in 1993 when Princeton biologist Bonnie Bassler found genes that allow some ocean-dwelling bacteria to emit a blue glow. The bacteria glow only when there are enough of them for the light to be visible. Bassler later found that many bacteria employ the same signaling system and respond to each other's signals, a finding that sparked widespread interest in the subject.
Scientists have now shown that at least 50 kinds of bacteria produce this signaling molecule, called autoinducer-2 or AI2, including E. coli and others responsible for human disease. "They are biding their time until they grow up to some critical population density at which they turn on their virulence factors," said Hughson. This trick may help the bacteria evade detection by the immune system during the earliest stages of infection, he said.
Although they knew the bacterial genes and proteins responsible for making and receiving the signal, Bassler and others could not identify the AI2 molecule itself. "They tried every trick in the book, basically everything you could think of," sai
Contact: Steven Schultz