"The stalk essentially increases the cell's reach into the environment but without the cost of increasing the cell's volume and surface area, which would be expensive from an energetic standpoint," Brun said.
Using mathematical models, the scientists showed that absorption of a nutrient using an antenna was a far more efficient morphology for nutrient uptake than alternate cell shapes in which the stalk plays no special role. The models assume the bacteria encounter nutrients via diffusion from their surrounding medium.
"Our report makes the point that in calm aquatic environments where there is no mixing of the liquid and therefore the motion of nutrient molecules is dominated by diffusion, it is the cell's length that is the most important parameter for nutrient uptake," Brun said.
"Imagine the nutrient molecule as a tiny tennis ball undergoing diffusion, that is bouncing back and forth off other molecules in random directions. It is easy to imagine that the tennis ball will be just as likely to make contact with a baseball bat as it will a tennis racket. And the longer the baseball bat, the larger the number of diffusing tennis balls that will make contact. That's why the stalk seems to be so advantageous for the cell. This is in contrast to cases where there is mixing of the liquid and where total surface area -- not length -- becomes more important. The stalk shape is advantageous in both situations because it increases surface area with minimal increase in volume, and at the same time it can be 15 or more times longer than the cell body."
The implications of the group's discovery are two-fold, Br
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Contact: David Bricker
brickerd@indiana.edu
812-856-9035
Indiana University
18-Jul-2006