Communication Between Bacteria and Eukaryotes
Bacteria also communicate with plants and animals. One striking example involves the Rhizobium bacterium, which helps fix nitrogen for legumes (such as pea and clover plants). This bacterium colonizes root hairs in specialized nodules built by the plant. Before the plant and bacteria ever come into contact, they are communicating. The plant sends out chemical signals, known as flavonoids, which penetrate Rhizobium cells and stimulate a gene-activating protein. The protein then switches on bacterial genes so that other proteins, such as Nod factor, are produced. Nod then stimulates the plant to form nodules.
Another example is the signaling between the luminous bacterium Vibrio fischeri and its host, the squid Eupryman scolopes. These bacteria colonize a specialized light organ on the squid, providing camouflage. The squid is a nocturnal forager; luminescence from the bacteria erases the shadow that would normally be cast from above by the moon's rays. Quorum sensing molecules allow the bacteria to turn on light production only when the colony has reached adequate density. However, the bacteria do not just communicate with one another - their chemical signals spur maturation of the light organ. Hatchling squid raised in sterile seawater do not develop the pouch that eventually houses the bacteria.
Like the Dr. Doolittle of fiction, who had the remarkable ability to talk with animals, scientists of the future will be continuing studies into the language of microbes.
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