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Bacteria's bodies are well-organized.

The insides of bacteria are far more organized than scientists ever had suspected, a team of Stanford University Medical Center researchers - Lucy Shapiro, chair of the School of Medicine's Department of Developmental Biology, and postdoctoral researchers Janine Maddock and Dickon Alley - has discovered. This group's finding debunks the commonly held belief - taught to biology students from grade school on - that bacteria are tiny bags of largely disorganized protoplasm. It was believed that their tiny size precluded any need for localized protein complexes.

"Bacteria are very little. It's always been assumed that they can carry out their business based on diffusion of molecules through the cell. Because bacteria are so little, a molecule that enters at one place can almost immediately find itself all the way across the cell. Unlike cells in higher organisms, bacteria don't have complex train tracks (something called the cytoskeleton) to get molecules around the cell," Shapiro notes.

However, Maddock and Shapiro have found that bacteria do have precisely placed protein complexes that carry out cellular functions. They demonstrate that, in Escherichia coli, proteins involved in directing the movement of bacteria in response to foods or poisons are clustered at the cell poles. In a sense, these protein clusters can be viewed as E. coli's nose.

This discovery adds to a growing body of evidence that the proteins making up bacteria are organized according to their functions. A few years ago, scientists began turning up results indicating that proteins involved in cell division band together to form a structure around the waist of the cell. "The bacterial cell is not what we thought it was. It's not just a bag of enzymes. And I predict that we're going to find specific localizations for many different kinds of protein complexes, each having unique functions. I think this is just the tip of the iceberg," Shapiro indicates.

The researchers started the project by trying to understand why the bacterium Caulobacter crescentus produces two distinct types of cell - one with a flagellum (appendage) and the other without. They found that the cells with flagella also were equipped with a chemical-sensing protein, known as a chemoreceptor. The bacteria with no flagella destroy their chemoreceptor proteins.

Shapiro, Alley, and Maddock then became curious about the location of the chemoreceptor protein in Caulobacter as well as E. coli. Examining the bacteria with an electron microscope, they found that the proteins were grouped together at the cells' poles. Moreover, the proteins clustered at the poles only when all three of the chemical-sensing proteins were present - the chemoreceptor and two other proteins known as CheA and CheW. "It turns out you need all three proteins holding hands in order for them to wind up in the right place on the cell. Now the questions are: How do these proteins get there? How does the bacterial cell know which end is up? How does it know there's an end in the first place?," Shapiro wonders.
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Publication:USA Today (Magazine)
Date:Jun 1, 1993
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