Rival colonies of bacteria can produce a lethal chemical that keeps competitors at bay, scientists report this week. By halting the growth of nearby colonies and even killing some of the cells, groups of bacteria preserve scarce resources for themselves, even when the encroaching colony is closely related.
"It supports the notion that each colony is a superorganism, a multicellular organism with it's own identity," said Eshel Ben-Jacob, an adjunct senior scientist at UC San Diego's Center for Theoretical Biological Physics and professor of physics at Tel Aviv University. Ben-Jacob and lead author Avraham Be'er of the University of Texas, Austin, and other colleagues at these institutions report their discovery in the early online edition of the Proceedings of the National Academy of Sciences.
Alone in a dish, colonies of the bacterium Paenibacillus dendritiformis will send branches of cells in all directions. But when forced to share a plate of limited nutrients with another colony, the branching patterns of both colonies become lopsided, leaving a space between the two.
It's not a lack of food that halts the growth. The researchers found nutrients in the gap, but they also found a protein there that wasn't present elsewhere on the dish. When they dabbed a bit of the purified protein on a fresh dish inoculated with P. dendritiformis, the bacteria formed a lopsided colony that shied away from the spot. And the cells at the edge of the colony closest to the suspect protein were dead.
They named the protein "sibling lethal factor," for its ability to kill even closely related colonies derived from a single original colony, and identified its gene. But the gene made a protein that was too large, heavier that the lethal factor by two-thirds and harmless. They concluded that some other factor must be in play.
Rather than guess, or poke about experimentally to figure out what was going on, Ben-Jaco
|Contact: Eshel Ben-Jacob|
University of California - San Diego