PASADENA, Calif.Using state-of-the-art electron microscopy techniques, a team led by researchers from Caltech has for the first time visualized and described the precise arrangement of chemoreceptorsthe receptors that sense and respond to chemical stimuliin bacteria. In addition, they have found that this specific architecture is the same throughout a wide variety of bacterial species, which means that this is a stable, universal structure that has been conserved over evolutionary time.
Their research, which was published this week in the online early edition of the Proceedings of the National Academy of Sciences (PNAS), may help scientists better understand the complex signaling pathways that are at the core of many biological processes.
Bacteria swim using flagella to propel themselves. But it's not as simple as that, explains Grant Jensen, associate professor of biology at Caltech and an investigator with the Howard Hughes Medical Institute (HHMI), who led the team. After all, they need to decide where to swim. "They tend to swim toward a favorable environment, and away from a harsh environment," Jensen says.
How do they know which is which? Enter the chemoreceptors, tiny protein molecules found at the front of the bacterium, near the flagella. "It's like a protein antenna that protrudes from the bacterial cell body, through the membrane, and out onto the surface," says Jensen. "It binds to nutrients and other chemical stimuli."
While swimming in a single direction, a bacterium such as Escherichia coli may encounter some nutrients, which then bind to the chemoreceptors. "This transmits a signal to the inside of the cell saying that things are good," says Jensen. "So the bacterium will keep swimming in the same direction. But if there are no good nutrients, the cell will do something called 'tumbling,' in which it stops and randomly flips over in the fluid, then starts swimming again in a random direction in
|Contact: Lori Oliwenstein|
California Institute of Technology